3©

?^o. 2 ^0

A MANUAL

OF THE

ANATOMY OF VERTEBRATED

ANIMALS.

BY

THOMAS H. HUXLEY, LL.D., F.R.S.,

AUTHOR OF "lay SEKMONS," "MAN's PLACE IN NATURE," "ORIGIN Or SPECIES,'

ETC., ETC.

NEW YOEK:
D. APPLETOlSr AND COMPANY,

1, 3, AND 5 BOND STKEET.

1886,

PREFACE.

The present work is intended to provide students of
comparative anatomy with a condensed statement of the
most important facts relating to the structure of verte-
brated animals, which have hitherto been ascertained.
Except in a very few cases, I have intentionally abstained
from burdening the text with references ; and, therefore,
the reader, while he is justly entitled to liold me respon-
sible for any errors he may detect, will do well to give
me no credit for what may seem original, unless his
knowledge is sufficient to render him a competent judge
on that head.

About two-thirds of the illustrations are original, the
rest * are copied from figures given by Agassiz, Bischoff,
Burmeister, Busch, Cams, Duges, Flower, Gegenbaur,
Hyrtl, Yon Meyer, Miiller, Pander and D Alton, Parker,
Quatrefages, and Traquair.

A considerable portion of the book has been in type
for some years ; and this circumstance must be my excuse
for appearing to ignore the views of several valued con-
temporaries. I refer more especially to those contained
in recently-published works of Professors Flower and
Gesienbaur.

London, September, 1871.

* Namely, figures 1, 6, 10, 11, 12, 13, 15, 18, 23, 26, 28, 29, 30, 31, 36, 39, 41,
42, 46, 50, 51, 54, 55, 56, 57, 58, 59, 60, 61, 75, 79, 82, 101, 107, 108, 109, 110.

CONTENTS.

VAOK

Cha.p T. — A General View of the Organization of the Yertebrata —

THE Vertebrate Skeleton, . . . . . . 7

II. — The Muscles and the Viscera — A General View of the

Organization op the Vertebrata, 44

ni. — The Provinces of the Vertebrata — The Class Pisces, . 100

IV, — The Class Amphibia, 149

V. — The Classification and the Osteology of the Eeptilia, . 167

VI. — The Classification and the Osteology of Birds, . . 233

VII. — The Muscles and the Viscera of the Sauropsida, . . 250

Vin. — The Classification and Organization of the Mammalia, . 2*73

THE A¥ATOM\'

OF

VEETEBEATED ANIMALS.

CHAPTER I.

> GENERAL YIEW OF THE 0EGANIZATT0:N" OF THE VEKTE-
BRATA THE VERTEBRATE SKELETON.

The Distiyictive Characters of the Yertebrata. — The Yerte^
brata are distinguished from all other animals by the circum-
stance that a transverse and vertical section of the body
exhibits two cavities, completely separated from one another
by a partition. The dorsal cavity contains the cerebro-spmal
nervous system ; the ventral, the alimentary canal, the heart,
and, usually, a double chain of ganglia, which passes under
the name of the " sympathetic." It is probable that this
sympathetic nervous system represents, wholly or partially,
the principal nervous system of the Annulosa and Mollusca.
And, in any case, the central parts of the cerebro-spinal ner-
vous system, viz., the brain and the spinal cord, would appear
to be unrepresented among invertebrated animals. For these
structures are the results of the metamorphosis of a part of
the primitive epidermic covering of the germ, and only acquire
their ultimate position, in the interior of the dorsal tube, by
tlie development and union of outgrowths of the blastoderm,
which are not formed in the Invertebrata.^

Again, in the partition between the cerebro-spinal and vis-

* It is possible that an exception to this rule may he found in the Ascid-
ians. The tails of the larvae of these animals exhibit an axial structure, which
has a certain resemblance to a vertebrate notochord ; and the walls of the
pharynx are perforated, much as in Ampliioxvs,

8 THE ANATOMY OF YERTEBRATED ANIMALS.

ceral tubes, certain structures, whicli are not represented in
invertebrated animals, are contained. During' the embryonic
condition of all vertebrates, the centre of the partition is occu-
pied by an elongated, cellular, cylindroidal mass — the noto-
chord, or chorda dorsalis. And this structure persists through-
out life in some Vertehrata ; but, in most, it is more or less
completely replaced by a jointed, partly fibrous and cartilag-
inous, and partly bony, vertebral column.

In all Vertehrata^ that part of the wall of the visceral tube
which lies at the sides of, and immediately behind, the mouth,
exhibits, at a certain stage of embryonic development, a
series of thickenings, parallel with one another and trans-
verse to the axis of the body, which may be five or more in
number, and are termed the visceral arches. The intervals
between these arches become clefts, which place the pharyn-
geal cavity, temjDorarily or permanently, in communication
with the exterior. Nothing corresponding with these arches
and clefts is kno^^m in the Invertehrata.

A vertebrated animal may be devoid of articulated limbs,
and it never possesses more than two pairs. These are always
pro^^ded with an internal skeleton, to which the muscles mov-
ing the limbs are attached. The limbs of invertebrated ani-
mals are commonly more numerous, and their skeleton is
always external.

When invertebrated animals are provided with masticatory
organs, the latter are either hard productions of the alimentary
mucous membrane, or are modified limbs. Vertebrated ani-
mals also commonly possess hard productions of the alimen-
tary mucous membrane in the form of teeth ; but their jaws
are always parts of the walls of the parietes of the head, and
have nothing to do with limbs.

All vertebrated animals have a complete vascular system.
In the thorax and abdomen, in place of a single peri-visceral
cavity in communication with the vascular system, and serving
as a blood-sinus, there are one or more serous sacs. These
invest the principal viscera, and may or may not communicate
witli the exterior — recalling, in the latter case, the atrial cavi-
ties of Mollusca.

In all Vertehrata^ except Amjyhioxus^ there is a single
valvular heart, and all possess an hejyatic portal system y the
blood of the alimentary canal never being wdiolly returned di-
rectly to the heart by the ordinary veins, but being more or
less completely collected into a trunk — the portal vein, which
ramifies through and supplies the liver.

THE DEVELOPMENT OF THE YERTEBKATA.

9

Tlie Developmeiit of the Vertebrata. — The ova of Verte-
brata have the same primaiy composition as those of other
animals, consisting of a germinal vesicle^ containing one or
many germinal Sjyots^ and included within a vitellus, upon the
amount of which the very variable size of the vertebrate ovum
chiefly depends. The vitellus is surrounded by a vitelline
membrane^ and this may receive additional investments in the
form of layers of albumen^ and of an outer, coriaceous, or cal-
cified shell.

The spermatozoa are always actively mobile, and, save in
some rare and exceptional cases, are developed in distinct
individuals from those which produce ova.

Fig. 1. — ^Dia^-ammatic section of the pregnant nterns of a decidnate placental mamma!
(Homo): ii, uterus; I, Fallopian tube; c, neck of the uterus; du, uterine decidua; (7s,
decidua serotina; dr. decidua rejle^xa; z,z,' villi; c/i, chorion; am amnion; «&,
umbilical vesicle ; c/^, aUautois.

Impregnation may take jolace, either subsequently to the
extrusion of the Gg^^ when, of course, the whole development
of the young goes on outside the body of the ompafous
parent ; or it may occur before the extrusion of the ^gg. In
the latter case, the development of the &gg in the interior of
the body may go no further than the formation of a patch of
primary tissue ; as in birds, where the so-called cicatricida^ or
" tread," which is observable in the new-laid ^gg., is of this
nature. Or, the development of the young maybe completed

10 THE ANATOMY OF VERTEBRATED ANIMALS.

while the egg remains in the interior of the body of the
parent, but quite free and unconnected with it ; as in those
vertebrates which are termed ovovivi2yarous. Or, the young
may receive nourishment from its vivijyarous parent, before
birth, by tlie close apposition of certain vascular appendages
of its body to the walls of the cavity in which it undergoes its
development.

The vascular appendages in question constitute the chief
part of what is called the placerita, and may be developed
from the umbilical vesicle (as in Mustelus among Sharks), or
from the allantois and chorion (as in most mammals). At
birth, they may be either simply detached from the substance
of the parental organism, or a part of the latter may be
thrown off along with them and replaced by a new growth.
In the highest vertebrates, the dependence of the young upon
the parent for nutrition does not cease even at birth ; but
certain cutaneous glands secrete a fluid called milk^ upon
which the young is fed for a longer or shorter time.

When development takes place outside the body, it may
be independent of parental aid, as in ordinary fishes ; but,
among some reptiles and in most birds, the parent supplies
the amount of heat, in excess of the ordinary temperature of
the air, which is required, from its own body, by the process
of incubation.

The first step in the development of the embryo is the
division of the vitelline substance into cleavage-inasses^ of
which there are at first two, then four, then eight, and so on.
The germinal vesicle is no longer seen, but each cleavage-
mass contains a nucleus. The cleavagfe-masses eventually be-
come very small, and are called emhryO'Cells, as the body of
the embryo is built up out of them. The process of yelk-
division may be either complete or partial. In the former
case, it, from the first, affects the whole yelk ; in the latter,
it commences in part of the yelk, and gradually extends to
the rest. The blastoderm^ or embryogenic tissue in which it
results, very early exhibits two distinguishable strata — an
inner, the so-called mucous stratum (/iT/poblast) , which gives
rise to the epithelium of the alimentary tract ; and an outer,
the serous stratum (ejnblast), from which the epidermis and
the cerebro-spinal nervous centres are evolv^ed. Between
these appears the intermediate stratum (mesoblast)^ which
gives rise to all the structures (save the brain and spinal mar-
row) which, in the adult, are included between the epidermis

THE DEVELOPMENT OF THE VERTEBRATA.

11

:>f the integument and tlie epithelium of the alimentary tract

and its appendages. o a \

A linear depression, the x>rimitive groove (i^ig. Z, A, c),
makes it appearance on the surface of the blastoderm, and

^^ T- O O

p <=■ c ilj-g

"- 'd gj fci is

_C a> o C /-I

i-, ^.a to

"Sis

. C3

^rS 1 tEfcc=l

a>

C3

S d ::; <n _a

'S

O rt 3
«C o' a> c3 p

cS O

CJ fl^

^ ^ a a

C3

c g*^ o's c^

^ -^ .-S S 'C! -^S i!i

-u y S ei O <" ®
O (3 -^ S-" <D "^ 3

'P O o C CO

2-5,

g

cS

<i> o -^ Tc G 9^ =°
J3 p a a rt^ 2

a^ «1:»"
2 t- *

'ban <s, ^

cc •:" r; a a fe ■ ■
v^ S :s a •" '""^

S-^ S-S sH =*

S . «■
®^ r»

a

C3

12 THE ANATOMY OF YERTEBEATED ANIMALS.

fclie substance of the mesoblast along eacli side of this groove
grows up, carrying with it the superjacent epiblast. Thus are
produced the two dorsal lammce^ the free edges of which arch
over toward one another, and eventually unite, so as to con-
vert the primitive groove into the cerebro-spinal canal. The
portion of the epiblast which linps this, cut off from the rest,
becomes thickened, and takes on the structure of the brain, or
Eticephalon^ in the region of the head; and of the spinal
cord, or Myelon, in the region of the spine. The rest of the
epiblast is converted into the epidermis.

The part of the blastoderm which lies external to the dor-
sal laminjB forms the ventral knnijice / and these bend down-
ward and inward, at a short distance on either side of the
dorsal tube, to become the walls of a ventral, or visceral,
tube. The ventral laminae carry the epiblast on their outer
surfaces, and the hypoblast on their inner surfaces, and thus,
in most cases, tend to constrict off the central from the
peripheral portions of the blastoderm. The latter, extending
over the yelk, encloses it in a kind of bag. This bag is the
first-formed and the most constant of the temporary, or foetal,
appendages of the young vertebrate, the umhilical vesicle.

YV^hile these changes are occurring, the mesoblast splits,
throughout the regions of the thorax and abdomen, from its
ventral margin, nearly up to the notochord (which has been
developed, in the mean while, by histological differentiation of
the axial indifferent tissue, immediately under the floor of the
primitive groove), into tw^o lamelloi. One of these, the visceral
lamella^ remains closely adherent to the hypoblast, forming
with it the splanclinopleure^ and eventually becomes the proper
wall of the enteric canal ; while the other, the parietal latnella^
follows the epiblast, forming with it the somatopleure^ which
is converted into the parietes of the thorax and abdomen.
The point of the middle line of the abdomen at which the
somatopleures eventually unite, is the umhilicus.

The walls of the cavity formed by the splitting of the
ventral laminae acquire an epithelial lining, and become the
great pleuroperitoneal serous membranes.

The Fodal Appendages of the Vertehrata. — At its outer
margin, that part of the somatopleure which is to be con-
verted into the thoracic and abdominal wall of the embryo,
grows up anteriorly, posteriony, and laterally, over the body
of the embryo. The free margins of this fold gradually ap-
proach one another, and, ultimately uniting, the inner layer
of the fold becomes converted into a sac filled with a clear

THE FCETAL ArPENDAGES.

13

fluid, tlie Ajnnloii / while the outer layer either disappears or
coalesces with the vitelline membrane, to form the Chorioii
(Fi-. d).

'~Avu

Fig. 8. —Later stasres of the deYelopment of the body of a Fowl than those represented in
Fig. 2. — E, embryo at the third day of incubation ; g, heart; h, eye; i, ear; k, visceral
arches and clefts ; ^, m, anterior and posterior folds of tiie amnion which have not yet
united over the body ; 1, 2, 3, first, second, and thu-d cerebral vesicles ; la, vesicle of the
third ventricle. — F, embryo at the fifth day of incubation. The letters as before, except
n, o, rudiments of the anterior and posterior extremities ; Ain, amnion ; All (the allan-
tois, hangring down from its pedicle) ; Um, umbihcal vesicle. — G-, uuder-view of the head
of the foregoing, the first viaceral ai-ch being cut away.

Thus the amnion encloses the body of the embryo, but not
the umbilical sac. At most, as the constricted neck, which
unites the umbilical sac with the cavity of the future intestine,
becomes narrowed and elongated into the vitelline duct, and
as the sac itself diminishes in relative size, the amnion, in-
creasing* in absolute and relative dimensions, and becoming
distended with fluid, is reflected over it (Fig. 1).

A third foetal appendage, the Allantois, commences as a
BinMe or double outo'rowth from the under surface of the meso-

U THE ANATOMY OF YERTEBRATED ANIMALS.

blast, behind the alimentary tract ; but soon takes the form
of a vesicle, and receives the ducts of the primordial hidneys^
or Wolffian bodies. It is supi^lied with blood by two arteries,
called Jiypogastrlc^ w^hich spring from the aorta ; and it varies
very much in its development. It may becom.e so large as to
invest all the rest of the embryo, in the respirator}^ or nutri-
tive, processes of which it then takes an important share.

The spUtting of the ventral laminse, and the formation of a
pleuroperitoneal cavity, appear to take place in all Vertebrata,
Usually, there is a more or less distinct umbilical sac ; but in
fishes and AmijJiihia there is no amnion ; and the allantois, if
it is developed at all, remains very small in these two groups.

Reptiles, birds, and mammals have all these foetal append-
ages. At birth, or when the ^^^ is hatched, the amnion
bursts and is thrown off, and so much of the allantois as lies
outside the walls of the body is similarly exuviated ; but that
part of it which is situated within the body is very generally
converted, behind and below, into the urinary bladder, and,
in front and above, into a ligamentous cord, the urachus, which
connects the bladder with the front wall of the abdomen. The
umbilical vesicle may either be cast off, or taken into the in-
terior of the body and gradually absorbed.

The majority of the visceral clefts of fishes and of many
Ampliihia remain open throughout life ; and the visceral
arches of all fishes (except A'mp)hioxns), and of all Ariiphibia,
throw out filamentous or lamellar processes, which receive
branches from the aortic arches, and, as hranchirje, subserve
respiration. In other Vertehrata all the visceral clefts become
closed and, with the frequent exception of the first, obliterated ;
and no branchiae are developed upon any of the visceral arches.

In all vertebrated animals, a system of relatively or abso-
lutely hard parts affords protection, or support, to the softer
tissues of the body. These, according as they are situated
upon the surface of the body, or are deeper seated, are called
exoslceleton^ or endosheleton.

The Vertebrate iLndoslceleton. — This consists of connective
tissue, to wdiich cartilage and bone may be added in various
proportions ; together with the tissue of the notochord and
its sheath, which cannot be classed under either of these heads.
The endoskeleton is distinguishable into two independant por-
tions — the one axial, or belonging to the head and trunk ; the
other, appendicular, to the limbs.

The axial endoslceleton usually consists of two sj'stems of

THE VERTEBRATE ENDOSKELETON. 15

skeletal parts, the sjnnal system^ and the cranial system, the
distinction between which arises in the following way in the
higher Vertebrata :

The primitive groove is, at first, a simple straight depres-
sion, of equal diameter throughout ; but, as its sides rise and
the dorsal laminae gradually close over (this process commen-
cing in the anterior moiety of their length, in the future ce-
phalic region), the one part becomes wider than the other, and
indicates the cephalic region (Fig. 4, A). The notochord,
which underlies the groove, terminates in a point at a little
distance behind the anterior end of the cephalic enlargement,
and indeed under the median of three dilatations which it
presents. So much of the floor of the enlargement as lies in
front of the end of the notochord, bends down at right angles
to the rest ; so that the anterior enlargement, or aoiterior cere'
bral vesicle, as it is now called, lies in front of the end of the
notochord ; the median enlargement, or the middle cerebral
vesicle, above its extremity ; and the hin-der enlargement, or
the posterior cerebral vesicle, behind that extremity (Fig. 4, D
and E). The under surface of the anterior vesicle lies in a
kind of pit, in front of, and rather below, the apex of the noto-
chord, and the pituitary gland is developed in connection with
it. From the opposite upper surface of the same vesicle the
pineal gland is evolved, and the part of the anterior cerebral
vesicle in connection with which these remarkable bodies arise,
is the future third ventricle.

Behind, the posterior cerebral vesicle passes into the primi-
tively tubular spinal cord (Fig. 4, A). Where it does so, the
head ends, and the spinal column begins ; but no line of de-
marcation is at first visible between these two, the indifierent
tissues which ensheath the notochord passing Avithout inter-
ruption from one region to the other, and retaining the same
character throughout.

The first essential differentiation between the skull and
the vertebral column is efi'ected by the appearance of the proto-
vertebroe. At regular intervals, commencing at the anterior
part of the cervical region, and gradually extending backward,
the indifi"erent tissue on each side of the notochord undergoes
a histological change, and gives rise to more opaque, quadrate
masses, on opposite sides of the notochord (Fig, 2, B, C).
Each pair of these gradually unite above and below that struct-
ure, and send arched prolongations into the walls of the spinal
canal, so as to constitute a proto vertebra.

No protovertebrae appear in the floor of the skull, so that,

16

TEE ANATOMY OF YERTEBRATED ANIMALS.

even in this early stage, a clear distinction is drawn between
the skull and the spinal column.

/j^^^^.-r

pfi 1 § j' lip

txi. i. — Successive stag'es of the development of the 'head of a Chick. I, II, III, first sec-
ond, and third cerebral vesicles ; la, vesicle of the cerebral hemisphere ; lb, vesicle of
the thiixl ventricle ; a, rudiments of the eyes and optic nerves ; b, of the ears ; g. of the
olfactory organs ; d, the infundibulum ; e. the ])ineal glaud ; c, protovertebrfe ; h. noto-
chord; 1, 2, 3, 4, 5, visceral arches; V, VII, VIII, the trigeminal, portio dura, and ninth
and tenth pairs of cranial nerves; k, the nasal process; I, the maxillary process; x, tlia
first visceral cleft. A. B, upper and under views of the head of a Chick at the end of
the second day. C, side-view at the third day. D. side-view at seventy-five hours. E,
side-view of the head of a Chick at the fifth day, which has been subjected to shght press-
Ore. F, head of a Chick at the sixth day, viewed from below.

OSSIFICATION OF THE VERTEBRAE. 17

Tlie Spinal System. — The protovertebrae consist at first
of mere indifFerent tissue ; and it is by a process of histologi-
cal differentiation within the protovertebral masses that, from
its deeper parts, one of the spinal ganglia and a cartilaginous
vertebral centrum — from its superficial layer, a segme7it of the
dorsal tnuscles, are produced.

Chondriiication extends upward into the w^alls of the dorsal
tube, to produce the oieural arch and S2yine of each vertebra ;
and, outward, into the wall of the thoracic and abdominal part
of the ventral tube, to give rise to the transverse processes and
ribs. In fishes, the latter remain distinct and separate from
one another, at their distal ends ; but, in most reptiles, in
birds, and in mammals, the ends of some of the anterior ribs,
on both sides, unite together, and then the united parts coa-
lesce in the middle line to form a median subthoracic cartilage
• — the sternum.

When ossification sets in, the centra of the vertebras are
usually ossified, in great measure, from ringlike deposits which
closel}^ invest the notochord ; the arches, from two lateral de-
posits, which may extend more or less into the centrum. The
vertebral and the sternal portions of a rib may each have a
separate ossific centre, and become distinct bones ; or the
sternal parts may remain always cartilaginous. The sternum
itself is variously ossified.

Between the completely-ossified condition of the vertebral
column and its earliest state, there are a multitude of grada-
tions, most of which are more or less completely realized in
the adult condition of certain vertebrated animals. The verte-
bral column may be represented by nothing but a notochord
with a structureless, or more or less fibrous, or cartilaginous
sheath, wdth or wdtliout rudiments of cartilaginous arches and
ribs. Or there may be bony rings, or ensheathing ossifications,
in its walls ; or it may have ossified neural arches and ribs
only, without cartilaginous or osseous centra. The vertebrae
may be completely ossified, with very deeply biconcave bodies,
the notochord remaining persistent in the doubly-conical inter-
vertebral substance ; or, ossification may extend, so as to ren-
der the centrum concave on one surface and convex on the
other, or even convex at each end.

Vertebrse which have centra concave at each end have
been conveniently termed amphicoelus ; those with a cavity
in front and a convexity behind, procoelus / where the position
of the concavity and convexity is reversed, they are opistho-
coelous.

18 TUE ANATOMY OF VERTEBRATED ANIMALS.

In the Jfaminalia, the centra of the vertebra3 are usually
flat at each end, the terminal faces being discoidal epiphyses^
developed from centres of ossification distinct from that of the
centrum itself.

The centra of the vertebra? may be united together by
synovial joints, or by ligamentous fibres — the intervertehral
li(faments. The arches are connected by ligaments, and gen-
erallv, in addition, by overlapping articular processes called
zygajyophijses^ or oblique processes.

In a great many Vertcbrata, the first and second cervical,
or atlas and axis^ vertebra? undergo a singular change ; the
central ossification of the body of the atlas not coalescing
with its lateral and inferior ossifications, but either persist-
ing as a distinct os odoiitoideum^or anchjdosing with the body
of the axis, and becoming the so-called odontoid process oi
this vertebra.

In Vertehrata with well-developed hind-limbs, one or more
vertebrae, situated at the posterior part of the trunk, usually
become peculiarly modified, and give rise to a sacrum^ with
which the pelvic arch is connected by the intermediation of
expanded and anchylosed ribs. In front of the sacrum the ver-
tebra? are artificially classed as cervical, dorsal, and lumbar.
Tlie first vertebra, the ribs of which are connected with the
sternum, is dorsal, and all those which lie behind it, and have
distinct ribs, are dorsal. Vertebrae without distinct ribs,
between the last dorsal and the sacrum, are lumbar. Ver-
tebra-", with or without ribs, in front of the first dorsal are
cervical.

The vertebrfB which lie behind the sacrum are cavdal or
cocci/f/eal. Very frequently, downward processes of these
vertebra? enclose the backward continuation of the aorta, and
may be separately ossified as subcaudal, or chevron, bones.

A tolerably complete segment of the spinal skeleton may
be studied in the anterior part of the thorax of a crocodile
(Fig. 5). It presents a proccelous vertebral centrum ((7),
united with which by the neurocentral suture is the neural
arch, which rises into the oieural spine (iV S.). Two pro-
cesses, the prezygapophyscs {Z), extend from the front part of
tlie arch, and have fiat articular surfaces turned dorsally. Two
others of similar form, but having their articular surfaces
turned ventrally, proceed from the posterior face of the
neural arch, and are the postzygapophyscs [Z'). By these,
which are often called oblique, or articular, processes, the ver-
tebra articulates with the corresponding processes ofits prede-

A SEGMENT OF THE SKELETON. 19

cessor or successor in the series. The transverse ijrocesses are
two on each side, one superior and one inferior. The former
(T.t) articuhites with the tuherculuin of the rib, the Litter
( Gp.t) with its capitulum. They may, therefore, be called ca-
intular and tuhtrcular transverse processes respectively. Each

Fig. 5. — A sej»Tnent of the endoskeleton in tbo anterior thoracic rej^ion of the body of a croc-
odile. — (7, the centrum or body of the vertebra ; N.S., tlio neural spine ; Z, the prezy-
gapophysis ; Z', the postzygapophyais ; T.t, the transverse process which articulates
with the tuberculum of the rib {t) ; Cp.t, that which articulates with the capitulum of
the rib \Cp); F.r, tlie ossiQed vertebral rib; V.r', the part of the vertebral rib which
remams cartilaginous ; St.r, the sternal rib ; St^ an artificially -separated segment of the
sternum ; P.u^ the uncinate process.

rib is divided by an articulation into a vertebral ( V.r) and a
sternal [St.r) part. The former remains unossified for a con-
siderable distance at its distal end ( Fir') ; the latter is more or
less converted into cartilage bone. The proximal end of the ver-
tebral rib bifurcates into a tuberculum {t) and a capitulum ( Cp),
The distal end of the sternal rib unites with the more or less os-
sified but unsegmented cartilage, which forms the sternum {8t),
A cartilaginous, or partly ossified, i«nciW<ife/)rocess (P.w.) pro-
jects from the posterior edge of the vertebral rib, over the in-
tercostal space. The student will find it convenient to famil-
iarize himself with the conception of such a spinal segment as
this, as a type, and to consider the modifications hereafter
described with reference to it.

In the majority of the Vertebrafa, the caudal vertebrne
gradually diminish in size toward the extremity of the body,
and become reduced, by the non-development of osseous pro-
cesses or arches, to mere centra. But, in many fishes, which
possess well-ossified trunk- vertebrjc, no distinct centra are
developed at the extremity of the caudal region, and the
notochord, invested in a more or less thickened, fibrous, or
cartilaginous sheath, persists. Notwithstanding this embry-

20

THE ANATOMY OF VERTEBRATED ANIMALS.

onic condition of the axis of the tail, the superior and inferior
arches, and the intersjDinous bones, may be completely formed
in cartilage or bone.

Whatever the condition of the extreme end of the spine
of a fish, it occasionally retains the same direction as the
trunk part, but is far more generally bent up, so as to form

THE CRANIAL SKELETON.

21

an obtuse angle with the hitter. In the former case, the ex-
tremity of the spine divides the caudal fin-rays into two nearly
equal moieties, an upper and a lower, and the fish is said to
be diphy cereal (Fig. 6, A). In the latter case, the upper di-
vision of the caudal fin-rays is much smaller than the lower,
and the fish is heterocercal (Fig. 6, B, C).

In most osseous fishes the hypural bones which support
the fin-rays of the inferior division become much expanded,
and either remain separate, or coalesce into a wedge-shaped,
nearly symmetrical bone, which becomes anchylosed with the
last ossified vertebral centrum. The inferior fin-rays are now
disposed in such a manner as to give the tail an appearance
of symmetry with respect to the axis of the body, and such
fishes have been called homocercal. Of these homocercalfish,
some (as the Salmon, Fig. 6) have the notochord unossified,
and protected only by bony plates developed at its sides. In
others (as the Stickleback, Percn, etc.), the sheath of the no-
tochord becomes completely ossified and united with the cen-
trum of the last vertebra, which then appears to be prolonged
into a bony urostyle.

Fig, 7. — ^The cartilaginous cranium of a Fowl at the sixth d^y of incubation, riewed from be-
low. — P, the pituitary space ; tr, the tralieculce^ uniting in front, in the bifurcated eth-
moYomerine plate; Qu. the quadrate cartilage; /Sb, the semicircular canals; C'o, the
cochlea ; A, the notochord imbedded in the basilar plate.

TJie Cranial System. — As has been stated, no protover-
tebrse appear on the floor of the skull ; nor is there any era™
nium, nor any developmental stage of a cranium, in which sep-
arate cartilaginous centres are known to occur in this region.

On the contrary, when chondrification takes place, it ex-
tends continuously forward, on each side of the notochord,

22 THE ANATOMY OF YERTEBRATED ANIMALS.

and usually invests the anterior termination of that body,
more or less completely, as a basilar plate.

The basilar plate does not extend under the floor of the
pituitary fossa, but the cartilage is continued forward on each
side of this, in the form of two bars, the traheculm cranii. In
front of the fossa, the trabeculae reunite and end in a broad
plate, usually bifurcated in the middle line — the ethmovome-
rine plate.

On each side of the posterior boundary of the skull, the
basilar cartilage grows upward, and meets with its fellow in
the middle line, thus circumscribing the occipital foramen^
and furnishing the only cartilaginous part of the roof of the
skull; for any cartilaginous upgrowths which maybe devel-
oped in the more anterior parts of the skull do not ordinarily
reach its roof, but leave a "svide, merely membranous space, or
fontanelle^ over the greater part of the brain.

Before the skull has attained this condition, the organs of
the three higher senses have made their appearance in pairs
at its sides ; the olfactory being most anterior, the ocular
next, the auditory posterior (Fig. 4).

Each of these organs is, primitively, an involution, or sac,
of the integument ; and each acquires a particular skeleton,
which, in the case of the nose, is furnished by the ethmovo-
merine part of the skull ; while, in that of the eyes, it apper-
tains to the organ, is fibrous, cartilaginous, or osseous, and
remains distinct from the skull. In the case of the ear, it is
cartilaginous, and eventually osseous : whether primitively dis-
tinct or not, it early forms one mass with the skull, immedi-
ately in front of the occipital arch, and often constitutes a very
important part of the walls of the fully-formed cranium.

The ethmovomerine cartilages spread over the nasal sacs,
roof them in, cover them externally, and send down a parti-
tion between them. The partition is the proper ethmoid, the
lamina perpendicularis of human anatomy; the posterolat-
eral parts of the ethmovomerine cartilages, on each side of the
partition, occupy the situation of the prefrontals, or lateral
masses of the ethmoid of human anatomy. The ingrowths of
the lateral walls, by which the nasal mucous membrane ac-
quires a larger surface, are the turhinals.

Ribhke cartilaginous rods appear in the first, second, and,
more or fewer, of the succeeding, visceral arches in all but the
lowest Vertehrata. The upper ends of the first and second of
these become connected with the auditory capsule, which Ues
immediately above them.

THE CRANIAL SKELETON.

23

Tlie first visceral arch bounds the cavity of the mouth be-
l)ind, and marks the position of the mandible or lower jaw.
The cartilage which it contains is termed MeckeVs cartilage.

The cartilaginous rod contained in the second visceral arch
of each side is the rudiment of the hyoidean apparatus. Like

Fig. 8. — TTncicr-v-lew of the head of a Fowl at the seventh day of incubation. — 7<7, the cere
bral hemispheres causing the integument to bulge ; a, the eyes ; g^ the olfactory sacs
^•, the fronto-nasal process ; Z, the maxillary process ; 1, 2, the fii-st and second visceral
arches ; cc, the remains of the first visceral cleft.

the preceding, it unites with its fellow in the ventral median
line, where the so-called " body " of the hyoid arises.

A ridge, continued forward from the first visceral arch to
the olfactory sac (Fig. 4, F ; Fig. 8, l)^ bounds the mouth on
each side, and is called the maxillary process, A cartilaginous
palato-pterygoid rod, developed in this process, becomes con-
nected with Meckel's cartilage behind, and with the prefrontal
cartilage in front.

The maxillary process is at first separated by a notch cor-
responding with each nasal sac, from the boundary of the
antero-median part of the mouth, which is formed by the free
posterior edge of 2i fronto-nasal process (Fig, 4, F ; Fig. 8, k).
This separates the nasal sacs, and contains the cartilaginous,
ethmovomerine, anterior termination of the skull. The notch
is eventually obliterated by the union of the fronto-nasal and
maxillary processes, externally ; but it may remain open in-
ternally, and then gives rise to the posterior nasal aperture^
by which the nasal cavity is placed in communication with
that of the mouth.

24 THE ANATOMY OF YERTEBRATED ANIMALS.

The General Modifications of the Vertebrate Skull. — The
lowest vertebrated animal, Amphioxus^ has no skull. In a
great many fishes, the development of the skull carries it no
further than to a condition which is substantially similar to
one of the embryonic stages now described ; that is to say,
there is a cartilaginous primordial cranium^ with or without
superficial granular ossifications, but devoid of any proper
cranial bones. The facial apparatus is either incompletely
developed, as in the Lamprey ; or, the upper jaw is repre-
sented, on each side, by a cartilage answering to the palato-
pter^^goid and part of Meckel's cartilage, while the larger,
distal portion of that cartilage becomes articulated with the
rest, and forms the lower jaw. This condition is observable
in the Sharks and Rays. In other fishes, and in all the higher
Vertehrata, the cartilaginous cranium and facial arches may
persist to a greater or less extent ; but bones are added to
them, which may be almost wholly membrane bones, as in the
Sturgeon ; or may be the result of the ossification of the car-
tilaginous cranium itself, from definite centres, as well as of
the development of superimposed membrane bones.

The Osseous Brain-case. — When the skull undergoes com-
plete ossification, osseous matter is thrown down at not fewer
than three points in the middle of its cartilaginous floor. The
ossific deposit, nearest the occipital foramen, becomes the hasi-
occipital bone ; that which takes place in the floor of the pitu-
itary fossa becomes the hasisphenoid ; that which appears in
the reunited trabeculee, in front of the fossa, gives rise to the
presphenoid. Again, in front of, and outside, the cranial cav-
ity, the ethmoid may be represented by one or more distinct
ossifications.

An ossific centre may appear in the cartilage on each side
of the occipital foramen, and give rise to the ex-occipital ^ and
above it, to form the supra-occipital. The four occipital ele-
ments, uniting together more or less closely, compose the oc-
cipital segment of the skull.

In front of the auditory capsules and of the exit of the
third division of the fifth nerve, a centre of ossification maj
appear on each side and give rise to the alisphenoid ; which,
normally, becomes united below with the basisphenoid.

In front of, or above, the exits of the optic nerves, the
itrhitosphenoidal ossifications may appear and unite below
with the presphenoid.

In front of the occipital segment, the roof of the sloill is
formed by membrane ; and the bones which complete the two

THE TYPICAL BONY SKULL.

25

segments of wliicli the basisplienoid and presplienoid form the
basal parts, are membrane bones, and are disposed in twa
pairs. The posterior are the parietals^ the anterior the fron-
tills y and the segments which they complete are respectively

o

I

^

4

1-1

H

CiJ

El

*-<

H

M

a

&

a

•

o

Q

o

H

c

1

c

1

— o
o

I

2

W

M

m

O

n

i

O

o

H

Q

g

O

M

f^

3

•

G?

i:

OQ

o
o

g

•

H

a

>:

o

I ■

H

1— ( '

— o -

■""0.
S

2

§

□Q

•
I— (

5

pq

•

-
<

s

d
S

M

^

M

S

M
H

o

— &< —

O

63

H

S

P4

Pketkontal.

1-3

hJ

a

i

o

tQ

il

g
w

Brancliial apparatus.

Ilyoidean apparatus.

o

I— I

M.andibu]ar Suspensorium.

o

W

02

Ah

o

<1

o

o

B

p

1^
•-a

Ah

<1

Hi

o

3

H

.=§

26 THE ANATOMY OF YERTEBRATED ANIMALS.

called ^jarietal ^iV,^ frontal. Thus the walls of the cranial cav-
ity in the typical ossified skull are di\^sible into three segments
— I. Occipital, II. Parietal, III. Frontal — the parts of which
are arranged with reference to one another, the sensory organs
and the exits of the first, second, fifth, and tenth pairs of
cranial nerves (i., n., Y., and x.), in the manner shown in the
diagram * on the preceding page.

The cartilaginous cases of the organs of hearing, or the
periotlc capsules^ are, as has been said, incorporated with the
skull between the ex-occipitals and the alisphenoids — or, in
other words, between the occipital and the parietal segments
of the skull. Each of them may have three principal ossifi-
cations of its own. The one in front is the probtic / the one
behind and below, the opisthotic / and the one which lies
above, and externally, the epiotic. The last is in especial re-
lation with the posterior vertical semicircular canal ; the first
with the anterior vertical semicircular canal, between which,
and the exit of the third division of the fifth nerve, it lies.
Tliese three ossifications may coalesce into one, as when they
constitute \kiQ 2')etrosal and inastoid parts of the temporal bone
of human anatomy ; or the epiotic, or the opisthotic, or both,
may coalesce with the adjacent supra-occipital and ex-occipi-
tals, leaving the prootic distinct. The prootic is, in fact, one
of the most constant bones of the skull in the lower Vertebra-
ta, though it is commonly mistaken, on the one hand for the
alisphenoid, and on the other for the entire petro-mastoid.
Sometimes a fourth, ^^^ero^/c ossification, is added to the three
already mentioned. It lies on the upper and outer part of the
ear-capsule between the prootic and the epiotic (see the fig-
ure of the cartilaginous cranium of the Pike, i7ifrd). 7> /Ji.

In some Vertebrata the base of the skull exliibits a long
and distinct splint-like mxcmbrane bone f — the parasphenoid^

* The names of the purely memhrane bones in this diagram are in large
capitals, as PARIETAL ; while those of the bones which are preformed in
cartilage are in smaller type, as Basisphek-qid.

t Bones may he formed in two ways. They may he preceded by cartilage,
and the ossific deposit in the place of the future bone may at first be deposited
in the matrix of that cartilage, or the ossific deposit may take place, from tiie
first, in indifferent, or rudimentary connective, tissue. In this case the bone
b not prefigured by cartilage. In the skulls of Elasmohranch fishes, and in
the sternum and epicoracoid of Lizards, the bony matter is simply ossified car-
tilage, or cartilage bone. The parietal or frontal bones, on the other hand,
are always devoid of cartilaginous rudiments, or, in other words, are memhrane
hones.

In the higher Verteh'ata the cartilage bones rarely, if ever, remain as such;
but the p-imitive ossified cartilage becomes, in great measure, absorbed ana
'■fcplaced by membrane bone, derived from the perichondrium.

THE BOXES OF THE FACE. 27

uhicli underlies it from tlie basi-occipital to the pre-splienoidal
region. In ordinary fishes and Ajmplvibia^ this bone ajipears
to replace the basisphenoid and presphenoid functionally,
while in the higher Vertehrata it becomes confounded with
the basisphenoid. The Vomer is a similar, splint-like, single
or double, membrane bone, which, in like manner, underlies
the ethmoid region of the skull.

In addition to the bones already mentioned, a prefrontal
l)one may be developed in the prefrontal region of the nasal
capsule, and bound the exit of^ the olfactory nerve externally.

K po8tfrontal bone may appear behind the orbit above the
alisphenoid. Sometimes it seems to be a mere dismember-
ment of that bone ; but, iu most cases, the bone so named is a
distinct membrane bone.

Furthermore, on the outer and upper surface of the audi-
tory capsule a membrane bone, the squamosal^ is very com-
monly developed ; and another pair of splint-bones, the nasals^
cover the upper part of the ethmovomerine chambers, in
which the olfactory organs are lodged.

TJie Osseous facial Ajjparatus. — Tlie bones of the face,
which constitute the inferior arches of the skull, appear with-
in the various processes and visceral arches which have been
enumerated. Thus, the prernaxillce are two bones developed
in the oral part of the naso-frontal process, one on each side
of the middle line, between the external nasal apertures, or
anterior nares^ and the anterior boundary of the mouth.

Ossification occurs in the palato-pterygoid cartilage at two
chief points, one in front and one behind. The anterior gives
rise to the palatine bone, the posterior to the pterygoid.
Outside these, several membrane bones may make their a[>
pearance in the same process. The chief of these is the max-
illa^ which commonly unites, in front, with the premaxilla.
Behind the maxilla there may be a second, the jugal j and
occasionally behind this lies a third, the quadrat o-jugal.

Between the maxilla, the prefrontal and the premaxilla,
another membrane bone, called lachrymal, from its ordinary
relation to the lachrymal canal, is very generally developed ;
and one or more supra-orhital and post-orhital ossifications
may be connected with the bony boundaries of the orbit.

When these and the postfrontal membrane bone are si-
multaneously developed, the}'' form two series of bony splints
attached to the lateral wall of the skull, one set above and
one below the orbit, which converge to the lachrymal. The

2S THE ANATOMY OF VERTEBRATED ANIMALS.

upper series (lachrymal, supra-orbital, post-frontal, squamosal),
terminates posteriorly over the proximal end of the quadrate
bone^ or mandibular suspensorium. The lower sei-ies (lachry-
mal, maxillary, jugal, quadrato-jugal) ends over the distal end
of that bone, with which the quadrato-jugal is connected.
The two series are connected behind the orbit by the post-
orbital (when it exists), but more commonly by the union of
the jugal "with the post-frontal and squamosal. The Ichthy^
osauria, Ghelonia, Crocodilia^ and some Lacertilkiy exhibit
this double series of bones most comjDletely.

Each nasal passage, at first very short, passes between the
premaxilla below, the ethmoid and vomer on the inner side,
the prefrontal above and externally, and tlie palatine behind,
to open into the forepart of the mouth. And, before the cleft
between the outer posterior angle of the naso-frontal process
and the maxillary process is closed, this passage communi-
cates laterally, with the exterior, and, posteriorly, with the
cavity of the orbit. When the maxillary and the naso-frontal
processes unite, the direct external communication ceases ;
but the orbito-nasal passage, or lachrymal canal, as it is
called, in consequence of its function of conveying away the
secretion of the lachrymal gland, may persist, and the lachry-
mal bone may be developed in especial relation with it.

In the higher Vertebrata, the nasal passages no longer
communicate \vith the forepart of the cavity of the mouth ;
for the maxillaries and palatines, regularly, and the pterygoid
bones, occasionally, send processes downward and inward,
which meet in the middle line, and shut off from the mouth
a canal which receives the nasal passages in front; while it
opens, behind, into the pharynx, by what are now the 2^oste-
rior nares.

Two ossifications commonly appear near the proximal end
of Meckel's cartilage, and become bones movably articulated
together. The proximal of these is the quadrate bone found
in most vertebrates, the m.alleus of mammals ; the distal is
the OS articulare of the lower jaw in most vertebrates, but
does not seem to be represented in mammals. The remainder
of Meckel's cartilage usually persists for a longer or shorter
tunc, but does not ossify. It becomes surrounded by bone,
arising from one or several centres, in the adjacent membrane,
and the ramus of the m>andible thus formed articulates with
the squamosal bone in mammals, but in other Vertebrata is

THE OSSEOUS MANDIBLE.

29

immovably united with the OS articulare. Hence the complete
ramus of the mandible articulates directly with the skull in
mammals, but only indirectly, or through the intermediation
of the quadrate, in other Vertehrata, In birds and reptiles,

f-mx;'

Fig. 9. — The head of a fcctal Lamb dissected so as to show Meckers cartilage, 31 ; the
malleus, w ; the iiicus, i; the tympanic, Ty ; the hyoid, //; the squamosal, Sq ;
pterygoid,/"^; palatine,^Z; laclirj'mal, Z ; premaxilla,^?«a!; nasal sac, it^; Eustachian
tube, Eu.

the proximal end of the quadrate bone articulates directly
(with a merely apparent exception in Opliidki)^ and indepen-
dentl}'' of the hyoidean apparatus, with the periotic capsule.
In most, if not all fishes, the connection of the mandibular
arch with the skull is effected indirectly, by its attachment to
a single cartilage or bone, the liyomcmdibular^ w^hich repre-
sents the proximal end of the hyoidean arch {see Fig. 24).

The ossification of the hyoidean apparatus varies immense-
ly in detail, but usually gives rise to bony lateral arches, and
a median portion, bearing much the same relation to them as
the sternum has to the ribs. When the lateral arches are com-
plete, they are connected directly with the periotic capsule.

The proximal end of the hyoidean arch is often united,
more or less closely, with the outer extremity of the bone,
called columella auris^ or stapes^ the inner end of which, in
the higner ^^ertehrata^ is attached to the membrane of the
fenestra ovalis.

In ordinary fishes, a fold of the integument extends back-
ward from the second visceral arch over the persistent bran*

30

THE ANATOMY OF VERTEERATED ANIMALS.

a

chial clefts ; within this is developed a series of raylike mem-
brane bones, termed opercular and brcmchiostegal, wliicli be-
come closely connected ^Yitll the hyoidean arch. A corre-
sponding process of the skin is developed in the Batrachian
Tadpole, and gTows backward over the branchia3. Its posterior
edge, at first free, eventually unites with the integument of
the body, behind the branchial clefts, the union being com*
pleted much earlier on the right side than on the left.

In most mammals a similar fold of integument gives rise
to the pinna, or external ear.

The branchial skeleton bears
the same relation to the posterior
visceral arches that the hyoidean
does to the second. When fully
developed, it exhibits ossified lat-
eral arches, connected by median
pieces, and, frequently, provided
with radiating appendages which
give support to the branchial mu-
cous membrane. It is only found
in those Vertehrata whicb breathe
by gills — the classes I^isces and
Amphibia. In the higher Verte-
brata, the posterior of the two
pairs of cornua, with which the hy-
oidean apparatus is generally pro-
vided, are the only remains of the
branchial skeleton.

The skull and face are usually
symmetrical in reference to a me-
dian vertical plane. But, in some
^etacea^ the bones about the re-
gion of the nose are unequally
^developed, and the skull becomes
asymmetrical. In the Flatfishes
{Pleuronectidoi)^ the skull be-
^ comes so completely distorted, that

FiG.lO.— ThesTviinofariaice(PZa/t-.«.<(a ,-. x ^ ^ ^ 1- 1 ^ •\ £

Tulf,ariH\ viewed froin above. The tlie twO CyCS lie On OUe Siclc Ot

dotted line «, 6 is the true morpho- x\\Q bodv, which is, in some cases,

losical median hne; 6>r, c'/-, the po- ^ c " -\ • \^ ji 'i/

Biiionof the twoeyes in their orbits; the Icit, and, in OtllCrS, the right

side. In certain of these fishes,
the rest of the skull and facial
bones, the spine, and even the
limbs, partake in this asymmetry. The base of the skull and

Eth, ethmoid ; Prf^ prefrontal ; Fr^
left frontal ; Fr\. rifrht fiontal ; Pa,
parietal; >S'6>, supra-occipital; Ep.O^
epiotic.

THE CARPUS AND THE TARSUS. 3i

its occipital region are comparatively little affected ; but, in the
intcrorbital region, the frontal bones and the subjacent carti-
laginous, or membranous, side-walls of the cranium are thrown
over to one side ; and, frequently, undergo a flexure, so that
they become convex toward that side, and concave in the op-
posite direction. The prefontal bone of the side from which
the skull is twisted, sends back a great process above the eye
of that side, which unites with the frontal bone, and thus en-
closes this eye in a complete bony orbit. It is along this
fronto-prefrontal bridge that the dorsal fin-rays are continued
forward, just as if this bridge represented the morphological
middle of the skull. (Fig. 10.)^

The embryonic Pleuronectidce have the eyes in their nor-
mal places, upon opposite sides of the head ; and the cranial
distortion commences only after the fish are hatched.

The Appendicular Endoskeleton. — The limbs of all verte-
brated animals make their appearance as buds on each side of
the body. In all but fishes, these buds become divided by
constrictions into three segments. Of these, the proximal is
called hrachhim in the fore-limbs, femur in the hind ; the
middle is antebrachiwn, or crus ; the distal is nianus, or pes.
Each of these divisions has its proper skeleton, composed of
cartilage and bone. The proximal division, normally, con-
tains only one bone, os humeri^ or humerus, in the brachium,
and OS femoris, ov femur, in the thigh ; the middle, two bones,
side by side, radius and ulna, or tibia and fibula ; the distal,
many bones, so disposed as to form not more than five longi-
tudinal series, except in the Ichthyosauria, where marginal
bones are added, and some of the digits bifurcate.

The skeletal elements of the manus and pes are divisible
into a proximal set, constituting the carpus or tarsus / and a
distal set, the digits, of which there are normally five, articu-
lated with the distal bones of the carpus and tarsus. Each
digit has a proximal hasi-digital {metacarjKtl or metatarsal)
bone, upon which follows a linear series of phalanges. It is
convenient always to count the digits in the same way, com-
mencingf from the radial or tibial side. Thus, the thumb is
the first digit of the hand in man ; and the great-toe the first
digit of the foot. Adopting this system, the digits may be
represented by the numbers i, ii, iii, iv, v.

There is reason to believe that, when least modified, the
carpus and the tarsus are composed of skeletal elements
which are alike in number and in arrangement. One of these,
primitively situated in the centre of the carpus or tarsus, is

32

THE ANATOMY OF VERTEBRATED ANIMALS.

termed the centrale ; on the distal side of this are five car-
palia, or tarsalia^ which articulate with the several metacar-
pal or metatarsal bones; while, on its proximal side, are
three bones — one radiate or tlhiale^ articulating with the radi-
us or tibia ; one ulnare or fihulare^ with the ulna or fibula ;
and one intennediwn^ situated between the foregoing. Car-
pal and tarsal bones, or cartilages, thus disposed are to be
met with in some Amphibia and Chelonia (Fig. 11), but,

Fig. 11. — The right fore-foot of the Chelonian Chelydra^ and the right hind-foot of the Am-
phibian Salamanclra. — U^ ulna; R, radius; F, fibula; 7", tibia.

Proximal carpal bones: r, radiale; t, intermedium ; w, ulnare; the centnJe is the middle
unlettered bone.

Proximal tarsal bones; t, tibiale; », intermedium; /, fibulare; c, centrale; 1, 2,8,4,6^
distal carpalia and tarsalia ; i, n, rn, iv, v, digits.

commonly, the typical arrangement is disturbed by the si:i3-
pression of some of these elements, or their coalescence with
one another. Thus, in the carpus of man, the radiale, inter-
medium, and ulnare are represented by the scaphoides^ lunare,
and cuneiforme respectively. The pisiforme is a sesamoid
bone developed in the tendon of the flexor carpi uhiaris,
which has nothing to do with the primitive carpus. The
centrale is not represented in a distinct shape, having proba
bly coalesced with one of the other elements of the carpus.
The fourth and fifth carpalia have coalesced, and form the
single unciforine. In the tarsus of man, the astragalus repre-
sents the coalesced tibiale and intermedium ; the calcaneum^
the fibulare. The naviculare is the centrale. Like the cor-

THE POSITION OF THE LIMBS. 33

responding bones in the carpus, the fourth and fifth tarsalia
have coalesced to form the cuboides.

The Position of the Limbs. — In their primitive position,
the Hmbs are straight, and are directed outward, at right
angles to the axis of the body; but, as develojDment proceeds,
they become bent in such a manner that, in the first place,
the middle division of each limb is flexed downward and
toward the middle line, upon the proximal division ; while
the distal division takes an opposite bend upon the middle
di^dsion. Thus the ventral aspects of the antebracliium and
cms come to look inwardly, and the dorsal aspects outwardly ;
while the ventral aspects of the manus and j^es look downward
and their dorsal aspects look upward. When the position of
the limbs has been no further altered than this, the radius in
the antebracbiura, and the tibia in the crus, are turned for-
ward, or toward the head ; the ulna and the fibula backward,
or toward the caudal extremity. On looking at these parts
with respect to the axis of the limb itself, the radius and the
tibia are pre-axial, or in front of the axis; while the ulna and
fibula are post-axial, or behind it. The same axis traverses
the centre of the middle digit, and there are therefore twc
pre-axial, or radial, or tibial digits ; and two post-axial, 01
ulnar, or fibular digits, in each limb. The most anterior of the
digits (i) is called pollex, in the manus ; and hallux in the pes.
The second digit (ii) is the index; the third (iii) the mediiis ;
the fourth (iv) the annularis ; and the fifth (v) the minimus.

In many Amphibia and Heptilia, the limbs of the adult do
not greatly depart from this primitive position ; but, in birds
and in mammals, further changes occur. Thus, in all ordi-
nary quadrupeds, the bracLium is turned backward and the
thio'h forward, so that both elbow and knee lie close to the
sides of the body. At the same time, the forearm is flexed
upon the arm, and the leg upon the thigh. In Man a still
greater change occurs. In the natural erect posture, the axes
of both arm and leg are parallel with that of the body, in-
stead of being perpendicular to it. The proper ventral sur-
face of the brachium looks forward, and that of the thigh
backward, while the dorsal surface of the latter looks forward.
The dorsal surface of the antebrachium looks outward and
backward, that of the leg directly forward. The dorsal surface
of the manus is external, that of the pes, superior. Thus,
speaking broadly, the back of the arm corresponds with the
front of the leg, and the outer side of the leg with the inner
side of the arm, in the erect position.

54 THE ANATOMY OF VERTEBRATED ANIMAIiJ.

In Bats, a line drawn from trie acetabulam to the foot is
also, in the natural position, nearly parallel with the long axis
of the body. But, in attaining this position, the leg is bent
at the knee and turned backward ; the proper dorsal surface
of the thigh looking upward and forward, while the corre-
sponding surface of the leg looks backward and upward, and
the ungual phalanges are turned backward.

The chief modifications of the manus and pes arise from
tlie excess, or defect, in the development of particular digits,
and from the manner in which the digits are connected with
one another, and with the carpus or tarsus. In the Ichthyo-
sauria and Plesiosauria, the Turtles, the Getacea and Sirenia^
and, in a less degree, in the Seals, the digits are bound together
and cased in a common sheath of integument, so as to form
paddles^ in which the several digits have little or no motion
on one another.

The fourth digit of the manus in the Ptzrosauria^ and the
four ulnar digits in tlie Bats, are vastly elongated, to support
the web which enables these animals to fly. In existing
birds the two ulnar, or post-axial, digits are aborted, the
metacarpals of the second and third are anchylosed together,
and the diiyits themselves are enclosed in a common inteofu-
mentary sheath ; the third invariably, and the second usually,
is devoid of a claw. The metacarpal of the pollex is anchy-
losed with the others, but the rest of that digit is free, and
frequently provided with a claw.

Amono^ terrestrial mammals, the most strikino: chano-es of
the manus and pes arise from the gradual reduction in the
number of the perfect digits from the normal number of five
to four [Sus), three {Jihinoceros), two (most Humi/iantia)^ or
one [E^uidoe).

The Pectorcd and Pehnc Arches. — The proximal skeletal
elements of each pair of limbs {humeri or femora) are sup-
ported by a primitively cartilaginous, ^;ec^o?'a^, or. pelvic
girdle, which lies external to the costal elements of the verte-
bral skeleton. This girdle may consist of a simple cartilagi-
nous arc (as in the Sharks and Kays), or it may be complicated
by subdivisions and additions.

The pectoral arch may be connected with tlie skull, or
with the vertebral column, by muscles, ligaments, or dermal
ossifications, though, primitively, it is perfectly free from, and
independent of, both ; but it is never united with the verte-^
br;je by the intermediation of i-ibs. At first, it consists of one

THE TECTOEAL ARCH.

35

continuous cartilage, on each side of the bod}^, distinguish-
able only into regions and processes, and affording an articular
surface to the bones or cartilages of the limb. But ossifica-
tion usually sets up in the cartilage, in such a way as to give
rise to a dorsal bone, called the scapula^ or shoulder-blade,
which meets, in the articular, glenoidal cavity for the hu-
merus, with a ventral ossification, termed the coracoid.

By difl'erences in the mode of ossification of the varioui?
parts, and by other changes, that region of the primitivelj?

ear

■m.cr

Fig. 12. — Side-view of the pectoral arch and sternum of a Lizard {Iguana fuderculata). —
)&, scapula ; s.sc, supra-scapula ; cr, coracoid ; gl, glenoidal ca\ity ; St, sternum ; a:8t,
xiphisternum ; ???..?c, mesoscapnla; p.cr, precoracoid; m.cr, mesocoracoid ; e.<»', epi-
coracoid ; cl, clavicle ; i.cl, interclavicle.

cartilaginous pectoral arch which lies above the glenoidal
cavity may be ultimately divided into a scapula and a supt'a-
scajnda / Avhile that which lies on the ventral side may pre-
sent not only a coracoid^ but a precoracoid and an epicora-
coid.

In the great majority of the Vertehrata above fishes, the
coracoids are large, and articulate with the antero-external
margins of the primitively cartilaginous sternum^ or breast-
bone. But, in most mammals, they do not reach the sternum,
and, becoming anchylosed with the scapula, they appear, in
adult life, as mere processes of that bone.

Numerous Vertebrates possess a clavicula, or collar-bone,
which is connected with the pre-axial margin of the scapida
and coracoid^ but takes no part in the formation of the
glenoid cavity, and is usually, if not alwaj's, a membrane
bone. In many Vertehrata, the inner ends of the clavicles

36

THE AKATOMY OF YERTEBRATED ANIMALS.

are connected with, and supported by, a median membrane
bone wliicb is closely connected with the ventral face of the
sternum. This is the mtei'clavicula, freq^j-^ntly called episteV'
nnm

^ise.

^icr-

Fig. 13.— Ventral view of the sternum and pectoral arches of Iguana tuherculata. The

letters as in Fig. 12.

The pelvic, like the pectoral, arch at first consists of a
simple continuous cartilage on each side, which, in Vertehrata
higher than fishes, is divided by the acetabulum^ or articular
cavity for the reception of the head of the femur, into a dorsal
and a ventral moiety.

Three separate ossifications usually take place in this car-
tilage — one in the dorsal, and two in the ventral, moiety.
Hence, the pelvic arch eventually consists of a dorsal portion,
called the ilium, and of two ventral elements, the pubis ante-
riorly, and the ischium posteriorly. All these generally enter
into the composition of the acetabulum.

The ilium corresponds with tlie scapula. In the higher
Vertebrata the outer surface of the latter bone becomes di-
vided by a ridge into two fossas. The ridge, called the sphie
of tlie scapula^ frequently ends in a prominent process termed
the acroraion^^M^ with this, in Mammalia, the clavicle artic-
ulates. In like manner, the outer surface of the ilium be-

TUE PELVIC ARCH.

37

iomes divided by a ridge wliicli grows out into a great crest
in Man and other Mammalia, and gives attachment to mus-
cles and ligaments.

The ischium corresponds very nearly with the coracoid in
the pectoral arch ; the pubis with the precoracoid, and more
or less of tlie epicoracoid.

The pelvis possesses no osseous element corresponding
witli the clavicle, but a strong* ligament, the so-called I^ou-
parfs ligament, stretches from the ilium to the pubis in many
J'^crtebrata and takes its place. (Fig. 14, Pp.)

Fig. ll. — Side-view of the left Os innominatum of Man : 7^, ilium; 7s. iscliiam ; 7^ pubis

A^ acetabulum ; Pjp, Poupai-t's ligament.

On the other hand, the marsupial hones of certain mam-
mals, which are ossifications of the tendons of the external
oblique muscles, seem to be unrepresented in the pectoral
arch ; while there appears to be nothing clearly corresponding
with a sternum in the pelvic arch, though the precloacal car'
tilage, or ossicle, of Lizards has much the sam.e relation to the
ischia as the sternum has to the coracoids.

Very generally, though not universally, the ilia are closely
articulated with the modified ribs of the sacrum. The pubes
and ischia of opposite sides usually meet in a median ventral
symphysis ; but in all birds, except the Ostrich, this union
does not take place.

The Limhs of Fishes. — The limbs of Fishes have an endo-
skeleton which only imperfectly corresponds with that of the
higher Vertebrates. For while homolo":ues of the cartilagi-

58

THE ANATOMY OF YERTEBRATED ANIMALS.

nous, and even of the bonj, constituents of tlie pectoral and
pelvic arches of the latter are traceable in Fishes, the cartila-
ginous, or ossified, basal and radial supports of the fins them-
selves cannot be identified, unless in the most general waj,
with the limb-bones, or cartilages, of the other Vertehrata.

In its least modified form, as in Lepidosiren^ the endo-
skeleton of the fish's fin is a simple cartilaginous rod, divided
into many joints; and articulated, by its proximal end, with
the pectoral arch. The £lasmohranchii possess three hasal
cartilages w^hich articulate with the pectoral arch, and are
called, respectively, from before backward — propterygial^ me-
sopterygial, and metapterygial hasalia. With these are artic-
ulated linear series of radial cartilages, upon which osseous,
or horny, dermal fin-rays are superimposed. (Fig. 15.)

Among the Ganoid fishes, the fins of Polypterus are, fun-
damentally, like those of the Elas'mohrancTiii ; but the pro-
pter3^gial, mesopter3^gial, and metapterygial hasalia^ are more
or less ossified, and are succeeded by a series of elongated
radialla, w^hich are also, for the most part, ossified. Beyond

Fla 1B.--Tht right pectoral member of the Monkish (Sgnafina): ^i, propterj'giani . r>t3,

mesopteiygium; ?/i^, metapteryg-iuui.

THE LIMBS OF FISHES. 39

tliese follow some small aclclitional radlaUa, which remain car-
tilaginous, and are embraced by the bases of the fin-rays. In
the other Ganoids the propterygial basale disappears, and
some of the radialia, pushing themselves between the meso-
pterygial and metapterygial basalia, articulate directly with
the pectoral arch. The mcsopterygial basale is embraced by,
and becomes more or less incorporated with, the large ante
rior fin-ray.

From these Ganoids the passage is easy to the Teleostei,
in which, also, the mesopterygial basale always becomes fused
with the anterior fin-ray, whence the latter seems to articulate
directly with the shoulder-girdle. Four bones, of very similar
general form, usually articulate with the pectoral arch, be-
neath and behind the mesopterygial basale and its fin-ray.
At their distal ends small cartilaginous nodules may lie, and
these are embraced by the fin-rays. Of these four bones, or
partially-ossified cartilages, the lowermost and hindermost
answers to the metapterygial basale of the Shark ; the others
seem to be radialia, [See the figure of the Pike's pectoral
fin, infra.) f I ij,

The ventral fins have basal and radial cartilages and fin-
rays, more or less resembling those of the fore-limbs.

In most Ganoids and Teleosteans the pectoral and pelvic
arches are, in part, or completely, ossified ; the former fre-
quently presenting distinct scapular and coracoid bones. To
these, in all Ganoids and Teleosteans, membrane bones, rep-
resenting a clavicle, with supra-clamcidar audi post-clavicular
ossifications, are added.

In all Elasmobranchs and Ganoids, and in a large propor-
tion of the Teleosteans, the pelvic fins are situated far back
on the mider side of the body, and are said to be " ventral "
in position ; but, in other Teleosteans, the ventral fins may
move forward, so as to be placed immediately behind, or even
in front of, the pectoral fins. In the former case they are
said to be " thoracic," in the latter " jugular."

The Vertebrate Exoskeleton. — The Exoskeleton never at-
tains, in vertebrated animals, the functional importance which
it so frequently possesses among the Invertehrata, and it va-
ries very greatly in the degree of its development.

The integument consists of two la3^ers — a superficial, non-
vascular substance, the epidermis^ composed of cells, which
are constantly growing and multiplying in the deeper, and
being thrown off in the superficial, layers ; and a deep vascu-
lar tissue, the dermis^ composed of more or less completely-

iO THE ANATOMY OF VERTEBRATED ANIMALS.

formed connective tissue. An exoskeleton maj be developed
by the hardening of either the epidermis, or the dermis.

The epidermal exoskeleton results from the conversion into
horny matter of the superficial cells of the epidermis. The
horny plates thus formed are moulded upon, and follow the
configuration of, areee, or processes, of the dermis. AVhen the
latter are overlapping folds, the horny epidermic investment
is called a scale, squama. When the dermic process is papilli-
form, and sunk in a pit of the dermis, the conical cap of modi-
fied epidermis which coats it is either a hair ot ^feather. To
become a hair, the horny cone simply elongates by continual
addition of new cells to its base ; but, in a feather, the horny
cone, which also elongates by addition to its base, splits up,
for a greater or less distance along the middle line of its undei
surface, and then spreads out into a flat vane, subdivided into
harbs^ harhules^ etc., by a further process of splitting of the
primary horny cone.

The epidermis remains soft and delicate in Fishes and
Amj)Jiihia. In Reptilia it sometimes takes the form of plates,
which attain a great size in many Ghelonia ^ sometimes, that
of overlapping scales, as in OpMdia and many Laoertilia ;
but, sometimes, it remains soft, as in some Chelonia and in the
Chamreleons. Epidermic plates in the form of nails appear
upon the terminal phalanges of the limbs.

All Aves possess feathers. In addition, the beak is partly
or completely ensheathed in horn, as in some Meptilia. Corni-
fied epidermic tubercles or plates are developed on the tarsi
and toes, the terminal phalanges of which (and sometimes
those of the wing) have nails. Besides these, some birds pos-
sess spurs, which are ensheathed in horn, on the legs or
wings.

In Mammalia^ the horny exoskeleton may take all the
forms already mentioned, except that of feathers. In some
Cetacea it is almost absent, being reduced to a few hairs, pres-
ent only in the foetal state. The Pangolin {Manis), on the
other hand, is almost completely covered wnth scales, the
Armadillos with plates, and most terrestrial mammals with a
tliick coat of hair. The greater part of the mass of the horns
of Oxen, Sheep, and Antelopes, is due to the epidermic sheath
which covers the bony core. Where the horny epidermis be-
comes very thick, as in the hoof of the Horse, and in the horn
of the Rhinoceros, numerous long papillas of the dermis extend
into it. These papillfB, however, are comparable to tlie ridges
of the bed of the nail, not to the papilla? of the hairs.

THE EXOSKELETON.

41

The dermal cxosl^eleton arises from the liardening of the
dermis ; in the majority of cases by the deposit of bone-earth,
in more or less completely-formed connective tissue, though
the resulting hard tissue has by no means always the struct-
ure of bone. It may happen that cartilage is developed in the
dermis ; and, either in its primary state or ossified, gives rise
to exoskeletal parts.

Fig. 16. — A, outline of a Pike (Ksocr), to show the fins : P, pectoral ; F, ventral ; J, anal ;
C caudal; Z*, dorsal, fins. Op., operculum; P.Op., preoperculum ; £i\ brancliiostegal
rays. — B, scales of the dermal exoskeleton of the same fish.

No dermal exoskeleton (except that of the fin-rays) is found
m the lowest fishes, Am^jhioxiis and the 3Iarsipohrancliii. In
most Teleostei, the integument is raised up into overlapping
folds ; and, in these, calcification takes place in lamina3, of
which the oldest is the most superficial, and lies immediately
beneath the epidermis. As a general rule, the calcified tissue
of the " scale " thus formed, does not possess the structure of
true bone in the Teleostei. But, in other fishes, the dermal
calcification may consist of true bone (as in the Sturgeon) ; or,
as in the Sharks and Rays, may take on the structure of teeth,
and consist mainly of a tissue exactly comparable to dentine,
capped with enamel, and continuous by its base with a mass
of true bone, which takes the place of the crusta x>etrofia^ or
cement of the teeth.

A form of dermal exoskeleton, which is peculiar to and
highly characteristic of fishes, is found in the Jin-rays. These
are developed in the integument either of the median line of
the body, or in that of the limbs. In the former case, they
usually enter into, or support, folds of the integument which
are termed dorsal^ caudal, or anal fins — according as they lie

i2 THE ANATOMY OF VERTEBRATED ANIMALS.

in the dorsal reg-ion, or at the extremity of the body, or on the
ventral aspect, behind the anus. Ordinary fin-rays are com-
posed of a hornlike, or more or less calcified, substance, and
are simjole at the base, but become jointed transversely, and
split up longitudinally, toward their extremities (Fig-. 6).
Each fin-ray consists of two nearly equal and similar parts,
which cohere hy their applied faces for the greater part of
their extent ; but, at the base of the rays, the halves commonly
diverge, to embrace, or more or less completely coalesce with,
cartilaginous or osseous elements of the exoskeleton. In the
median fins, these are the intersjnnous cartilages, or bones,
which lie between the fin-rays and the superior or inferior
spines of the vertebras. In the paired fins, they are radial or
basal, cartilaginous or osseous, elements of the endoskeleton.

The Artiphibia in general are devoid of dermal exoskeleton,
but the CcecAlicB have scales like those of fishes. CeratopJirys
has plates of bone developed in the dorsal integument, which
seem to foreshadow the plates of the carapace of the Cheloniaj
and the extinct Labyrinthodonts possessed a very remarkable
ventral exoskeleton.

The Ophidia have no dermal exoskeleton. Many Lizards
have bony dermal plates corresponding in form and size with
the epidermal scales. All Grocodilia have such bony plates
in the dorsal region of the body and tail ; and in some, such
as the Jacares and Caimans, and the extinct Teleosauria, they
are also developed in the ventral region. In these animals
there is a certain correspondence between the segments of the
exoskeleton and those of the endoskeleton. But the dermal
exoskeleton attains its greatest development in the Ghelorda^
and will be particularly described under the head of that order.

In the JSIammalia the development of a dermal exoskeleton
is exceptional, and occurs only in the loricated Edeniata^ in
which the dorsal region of the head and body, and the whole
of the tail, may be covered with shields of dermal bone.

In connection with the dermis and epidermis, the glandu-
lar and pigmentary organs of the integument may be men-
tioned. Integumentary glands do not appear to exist in
Fishes, but they attain an immense development in some of
the AmpJdbia^ as the Frog. Among Jleptilia^ Lizards fre-
quently present such glands in the femoral and cloacal regions ;
and, in Crocodiles, integumentary glands, wdiich secrete a
musky substance, lie beneath the jaw. In Birds they attain a
considerable size in the uropygial gland ; and, in Maniincdia^
acquire a large development in connection Avith the sacs of the

TUE EXOSKELETON. 43

hairs, or as indepeudcnt organs, in tbe form of sweat-glands,
musk-glands, or mammary glands.

The color of the integument may arise from pigment-
granules, deposited either in the epidermis or in the dermis ;
and, in the latter case, it is sometimes contained in distinct
chromatophores, as in the Chamceleon,

CHAPTER n.

THE MUSCLES AISTD THE TISCERA A GENERAL VIEW OF TflE

OEGANIZATION OF THE VERTEBEATA.

The muscular system of the T^ertebrata consists of muscles
related partly to the exoskeleton, partly to the endoskeleton,
and partly to the viscera, and formed both of striated and un-
striated muscular fibre. The latter is confined to the vessels,
the viscera, and the integument ; the parts of the endoskele-
ton being moved upon one another exclusively by striated mus-
cular fibre. The muscles of the endoskeleton may be divided,
like the endoskeleton itself, into one system appertaining to
the trunk and head, and another belonging to the limbs.

The JIuscular System of the Trunk and Head. — This con-
sists of two portions, which differ fundamentally in theii
origin, and in their relations to the endoskeleton. The one
takes its origin in the protovertebrse ; each protovertebra be-
coming differentiated, as we have seen, into three parts ; a
spinal ganghon and a segment of the vertebral endoskeleton,
in the same plane, and a more superficial sheet of muscular
fibres. These muscular fibres are consequently situated above
the endoskeleton, or are episkeletal. Other muscular fibres are
developed below the endoskeleton, and may be termed hypo-
skeletal muscles. The hyposkeletal muscles are separated from
the episkeletal, not onlj' by the endoskeleton of the trunk (or
the vertebras and their prolongations, the ribs), but by the
^'entral branches of the spinal nerves.

As the episkeletal muscles are developed out of the proto-
vertebrae, they necessarily, at first, present as many segments
is there are vertebrae, the interspaces between them appearing
as intermuscular septa. The development of the hyi^oskeleta]
muscles has not been worked out, but it appears to take jJace
much later than that of the episkeletal set.

EriSKELETAL AND IIYFOSEELETAL MUSCLES. 45

In the lowest Yertehrata — as, for example, in ordinary
fishes — the chief muscular system of the trunk consists of the
episkeletal muscles, which form thick lateral masses of longitu-
dinal fibres, divided by transverse intermuscular septa into
segments (or Myotomes) corresponding with the vertebrte.
The lateral muscles meet in the middle line below, and divide,
in front, into a dorso-lateral mass connected with the skull,
and a ventro-lateral attached, in part, to the pectoral arch, and,
in part, continued forward to the skull, to the hjoidean appa-
ratus, and to the mandible. Posteriorly, the lateral muscles
are continued to the extremity of the tail. The hyposkeletal
muscular system appears to be undeveloped.

In the higher Yertehrata^ both the episkeletal and hypo-
skeletal muscular systems are represented by considerable
numbers of more or less distinct muscles. The dorso-lateral
division of the lateral muscle of the fish is represented b}' the
superior caudal muscles, and by the erector spinoe • which, as
it splits up, anteriorly, and becomes attached to the vertebrie,
and to the ribs, and to the skull, acquires the names of spi-
nalis^ semispi7iaUs, longissiniKS dorsi, sacrolumhalis, i7iter-
tr ail sver sails, levatores costarmn, complexiis, sptle^iius, recti
p)ostici, and 7'ecti later ales.

The ventro-lateral division of the fish's lateral mnscle is
represented, in the middle line of the trunk and head, by a
series of longitudinal muscles ; and, at the sides, by obliquely-
directed muscles. The former are the recti ahdomi^iis, extend-
ing from the pelvis to the stern vim — the sterno-Jiyoidei, be-
tween the sternum and the hyoidean apparatus — the genio-
hyoidei, which pass from the hyoid to the symphysis of the
mandible. The latter are the ohliqui exteymi of the abdomen
— the external intercostales of the thorax — the sifbclaviifs
stretching from the first rib to the clavicle ; the scaleoii from
the anterior dorsal ribs to the cervical ribs and transverse
processes, and the ster^io- and cleido-niastoidei from the ster-
num and clavicle to the skull.

The fibres of all these obhque muscles take a direction,
from parts which are dorsal and anterior, to others which are
ventral and posterior.

The trunk muscles of the lower Amphibia exhibit arrange-
ments which are transitional between those observed in Fishes
and that which has been described in Man, and which substan-
tially obtains in all abranchiate Yertehrata.

The muscles of the jaws and of the hyoidean apparatus
appear to be, in part, episkeletal, and, in part, hj^poskeletal.

46 THE ANATOMY OF VERTEBRATED ANIMALS.

The mandible is depressed by a muscle, the digastric^ arising
from the skull, and supplied by a branch of the seventh nerve :
it is raised by a muscular mass, which is separable into mas-
seter, temporal, and pterygoid muscles, according to its con-
nection with the maxillo-jugal bones, the sides of the skull,
or the palato-pterygoid bones, and is supplied by the fifth
nerve.

The proper facial muscles belong to the system of cutane-
ous muscles, and receive branches from the seventh nerve.

The hyposkeletal system is formed, partly, of longitudinal
muscles which underlie the vertebral column ; and partly, of
more or less oblique, or even transverse fibres, w4iich form the
innermost muscular walls of the thorax and of the abdomen.

The former are the subcaudal intrinsic flexors of the tail ;
the pyriformis, psoas, and other muscles proceeding from the
inferior faces of the vertebrae to the hind-limb; the longus
colli, or intrinsic flexor of the anterior part of the vertebral
column ; and the recti capitis antici, or flexors of the head
upon the vertebral column. The latter are the ohliquus in-
ter nus of the abdomen, the fibres of which take a direction
crossing that of the external oblique muscle ; and the trans-
versalis, which lies innermost of the abdominal muscles, and
has its fibres transverse. In the thorax, the intercostales interni
continue the direction of the internal oblique, and the triangu-
laris sterni that of the transversalis. The diaphragm and the
levator ani must also be enumerated among the hyposkeletal
muscles. The hyposkeletal muscles of the posterior moiety
of the body attain a great development in those Vertebrata
which have no hind-limbs, such as Ophidia and Getacea.

The Muscular System of the Limbs. — The muscles of the
limbs of Fishes are very simple, consisting, on each face of
the limb, of bundles of fibres, w4iich proceed (usuall}'- in two
layers) oblivquely, from the clavicle and supraclavicle to the
fin-rays. The pectoral and pelvic arches themselves are im-
bedded in the lateral muscles.

In the Amp>hibia and all the higher Vertebrata, the muscles
of the limbs are divisible into — intrinsic, or those wdiich take
their origin within the anatomical limits of the limb (including
the pectoral or pelvic arch) ; and extrinsic, or those which
arise outside the limb.

Supposing the limb to be extended at right angles to the
spine (its primitive position), it will present a dorsal aspect
and a vetitral aspect, with an anterior, or pre-axlal^ and a pos-
terior, or post-axial^ side.

THE MUSCLES OF THE LIMBS. 41

In the Vertehrata above fishes, the following muscles, which
occur in Man, are very g^enerally represented :

JExtrinsic muscles attached to the i)ectoral and pelvic arches^
on the dorsal aspect. — In the fore-limb, the cleidomastoidetis^
from the posterolateral region of the skull to the clavicle ; the
trajyezlus^ from the skull and spines of many of the vertebra)
to the scapula and clavicle ; the rhonihoidei^ from the spines
of vertebrae to the vertebral edge of the scapula, beneath the
foregoing. Sometimes there is a tracheloacroinicdis^ from the
transverse processes of the cervical vertebra) to the scapula.

On the ventral aspect^ the siihclavius, w^hich passes from the
anterior rib to the clavicle, may be regarded as, in part, a mus-
cle of the limb ; the pectoralis minor ^ from the ribs to the
coracoid.

Between the dorsal and the ventral aspects muscular fibres
arise from the cervical and dorsal ribs, and pass to the inner
aspect of the vertebral end of the scapula : anteriorly, these are
called levator angidi scapidcE ^ posteriorly, serratus magnus.

An omohyoid muscle frequently connects the scapula with
the hyoidean arch.

The posterior limb does not seem to offer any muscles ex-
actly homologous Avith the foregoing. So far, however, as the
recti abdominis^ the ohliqiius exter7ius^ and the fibres of the
erector spinoe^ are attached to the pelvic girdle, they cor-
respond in a general way with the pre-axial, or protractor, mus-
cles of the pectoral arch ; and the ischio-coccygeal muscles,
when they are developed, are, in relation to the pelvic arcli,
retractors, though, owing to the relative fixity of the pelvis,
they act in protracting, or flexing, the caudal region.

The p)Soas rninor^ proceeding from the under surfaces of
posterior dorsal (or lumbar) vertebrae to the ilium, or pubis,
is a protractor of the pelvis, but, as a hyposkeletal muscle,
has no homolcgue in the fore-limb.

Extrinsic muscles attached to the humerus or femxir^ on
the dorsal aspect. — In the fore-limb there is the post-axial latis-
simits dorsi passing from spines of dorsal vertebrae to the
humerus. On the ventral aspect., the pectoralis major extends
from the sternum and ribs to the humerus.

In the hind-limj, the glutcBus maximus^ so far as it arises
from the sacral and coccygeal vertebrae, and is inserted into
the femur, repeats the relations of the latissitnus dorsi. In
the absence of any thing corresponding with the sternum, or
the ribs, no exact homologue of the pectoralis mc(jor can be
said to exist, though the pectineus comes near it. The psoas

48 THE ANATOMY OF YERTEBRATED AXIMALS.

m,ajo7\ passing from posterior dorsal or lumbar vertebrae — tLe
pyriformis from sacral vertebrae — the femoro-coccygeiis (when
it exists) from caudal vertebrae — to the femur, are all hypo-
skeletal muscles, without homologues in the anterior extremity.

All the other muscles of the limbs are i?itri7isic^ takinnr
their origins from the pectoral or peivic arches, or from some
of the more proximal segments of the limb-skeleton, and hav-
ing their insertion in the more distal segments. They are
thus arranged in Man and the higher Marti'inalla :

Intrinsic muscles proceeding from the pectoral or pelvic
arches to the humerus or femur ^ on the dorsal aspect. — In the
fore-limb, the deltoides proceeds from the clavicle and scapula
to the humerus. This superficial shoulder-muscle continues
the direction of the fibres of the trapezius ^ and, when the
clavicle is rudimentary, the adjacent portions of the two mus-
cles coalesce into a cephalo-humeralis muscle. Beneath the
deltoid the supra-spinatus^ on the pre-axial side of the spine
of the scapula ; the infraspinatus, and the teres major and
minor, on its post-axial side, run from the dorsal aspect of the
scapula to that of the head of the humenis.

In the hind-limb, the tensor vagince femoris, which passes
from that part of the ilium which corresponds with the spine
and acromion of the scapula, to the femur, appears to answer
better to the deltoid than does the glutceus maximus, which,
at first sio-ht, would seem to be the homoloo*ue of that muscle.

The iliacus, proceeding from the inner surface of the crest
of the ilium to the smaller trochanter, answers to the supra-
spinatus y the glutams medius and m,inimus, which arise from
the outer surface of the ilium, to the infra-sp>inatus and teres.

In the fore-limb, a muscle, the subscapidaris, is attached
to the inner face of the scapula, and is inserted into the hu-
merus. No muscle exactly corresponding with this appears
to exist in the hind-limb.

On the ventral as^^yect in the fore-limb, the coracohrachialis
pass.es from the coracoid to the humerus. In the hind-limb, a
number of muscles proceed from the corresponding (ischio-
pubic) part of the pelvic arch to the femur. These are, from
the outer surface of the pubis, the p>ectineus, and the great ab-
ductors oi the femur; with the obturator exter?ius, from the
outer side of the ischiopubic fontanelle, or obturator membrane.
The getnelli and tlie quadratus fenioris take their origin from
the ischium.

No muscle is attached to the proper inner surface of the
ilium, so that there is no homologue of tlie subscapularis in

THE MUSCLES OF THE LIMBS. 49

the hind-limb. On the other hand, a muscle, the obturator
iiiternus^ attached to the inner surface of the ischiopubic fon-
tanelle, and winding round to the femur, has no homologue in
the upper extremity of the higher Vertebrata, unless it be the
so-called coracohxichlalls^ which arises from the inner surface
of the coracoid in many Saiirojjsida.

Jfuscles of the Antebrachiwn and Crus. — On the dorsal
isjject of the fore-limb, as of the hind-limb, certain muscles
arise in part from the arch, and, in part, from the bone of the
proximal segment of the limb, and go to be inserted into the
two bones of the second segment. These are, in the fore-
limb, the triceps extensor and the supinator brevis j in the
hind-limb, the quadriceps extensor.

There is this difference between these two homolosrous
groups of muscles — that in the fore-limb, the principal mass
of the muscular fibres goes, as the triceps, to be inserted into
the post-axial bone (ulna), and the less portion, as supinator
brevis, into the pre-axial bone (radius) ; whereas, in the hind-
limb, it is the other way, almost the whole of the muscular
fibres passing, as the quadricej^s, to the pre-axial bone (tibia),
the tendon commonly developing a sesamoid patella/ while
only a few fibres of that division of the quadriceps which is
called the " vastus externus " pass to the post-axial bone
(fibula).

On the ventral aspect, the fore-limb presents three mus-
cles, arising either from the pectoral arch, or from the hume-
rus, and inserted into the two bones of the forearm. On the
pre-axial side are two muscles ; one double-headed, the biceps,
arising from the scapula and the coracoid, and inserted into
the radius. A second, the supbiator longus, passes from the
humerus to the radius. On the post-axial side, the brachialis
anticus arises from the humerus, and is inserted into the ulna.
The hind-limb has two muscles, the sartorius, arising from the
ilium, and the gracilis, from the pubis, in place of the biceps
brachii, and inserted into the pre-axial bone, the tibia, which
corresponds with the radius. Two other muscles, the semi-
membranosus and semi-tendinosus, pass from the ischium to
the tibia, and replace, without exactly representing, the su-
pinator longus. Corresponding with the brachialis anticus
is the short head of the biceps femor is, vcc'x^Xw^ivom. the femur,
and inserted into the post-axial bone of the leg, the fibula.
The long head of the biceps femor is, which proceeds from the
ischium, appears to have no representative in the fore-limb.

In the fore-limb, a muscle, the pronator teres, passes ob-
3

50 THE ANATOMY OF VERTEBRATED ANIMALS.

liquely from the post-axial condyle of the humerus to the radi-
us. In the hind-limb, a corresponding muscle, the poplitmiis^
proceeds from the post- axial condyle of the femur to the tibia.
The pronator quadratus^ which passes from the ulna to the
radius, has its analogue, in some MarsupiaUa and B,eptilia^
in muscles which extend from the fibula to the tibia.

The Muscles of the Digits. — The remaining muscles of the
two limbs are, primarily, muscles of the digits, and are at>-
tached either to the basi-digital (metacarpal or metatarsal)
bones, or to the phalanges, though they may acquire second-
ary connections with bones of the tarsus or carpus. The
plan upon which they are arranged, when they are most com-
pletely developed, will be best understood by commencing
with the study of their insertion in any one of those digits
which possesses a complete set ; such, for example, as the
fifth diofit of the manus, or little fino-er, in Man and the hi^^rher
Primates.

On the dorsal aspect this digit presents : first, attached to
the base of its metacarpal bone, the tendon of a distinct mus-
cle, the extensor carpi ulnaris. Secondly, spreading out over
the phalanges into an aponeurosis, which is principally at-
tached to the first and second, is a tendon belonging to another
muscle, the extensor rninhni digiti. Thirdly, entering the same
expansion is one tendon of the extensor communis digitoruyn.

On the 'central aspect there are : first, attached to the base
of the metacarpal, the tendon of a distinct muscle, the jfexor
carpi ulnaris / secondly, arising from the sides and ventral face
of the metacarpal, and inserted into either side of tlie base of
the proximal phalanx, two muscles, the inter ossei j thirdly,
inserted into the sides of the middle phalanx by two slips, a
tendon of the flexor perforatus / and fourthh^, passing be-
tween these two slips, and inserted into the base of the distal
phalanx, a tendon of the flexor perforans. Thus there are
special depressors, or flexors, for each segment of the digit.
There appear, at first, to be but three elevators, or extensors,
but, practically, each segment has its elevator. For the ten-
dons of the extensor communis and extensor minimi digiti are
attached to the middle and the proximal phalanges ; and the
distal plialanx is specially elevated by tlie tendons of two lit-
tle muscles, which, in Man, are usually mere subdivisions of
the interossei, and pass upward, joining the extensor sheath,
to be finally inserted into the distal phalanx.

The fifth digit of the pes, or little toe, sometimes presents
the same disposition of muscles, namel}" :

THE MUSCLES OF TUE LIMES.

51

On the dorsal aspect : first, the peroyiaeus tertlus for the
metatarsal bone ; secondly, one tendon from the extensor digi"
torum brevis^ but this last is commonly absent in Man ; third*
ly, one tendon from the extensor digitormn longus.

'Jlx^.2,^

Fig. 17. — Part of the middle digit of the manus of an Orang- with the flexors and extensors
of the phalanges: mcp.^ metacarpal bone; Ph. 1, Ph. 2, Ph. 3, the three phalanges;
Ext. 1, the deep long extensor tendon from the extetisor indicis ; Ext. 2, the supei-fl-
cial long extensor tendon fi-om the extensor comimmis ; I. e., the interosseous short ex-
tensor ; /./;, the interosseous short flexor ; E. pns., the deep long flexor (jper/orans) ; E.
pts., the superficial long flexor (j)er/oratus).

On the ventral aspect : first, \kvQ peronmus hrevis.^ attached
to the base of the metatarsal ; secondly, two mterossei y
thirdly, a perforated flexor ; and fourthly, a perforating flexor,
like those of the manus. The divisions of the mterossei^
which send tendons to the extensor sheath on the dorsum of
the digits of the foot in Man, are hardly distinct from the ven-
tral divisions of those muscles.

In addition to the muscles which have been mentioned, the
fifth digit has an abductor and an adductor^ which may be
regarded as subdivisions of the mterossei, arising within the
manus or pes, and inserted into opposite sides of the proximal
phalanx ; and an oppo7ie7is, a muscle attached to the ventral
face of the carpus or the tarsus, and inserted into the post-
axial edge of tlie shaft of the metacarpal or metatarsal.

Finall}^, a lumbricalls muscle proceeds from the tendon of
the perforating flexor, on the pre-axial side of the digit, to
the extensor sheath.

None of the other digits of the manus, or of the pes, has a
greater number of muscles than this ; in fact, all the others
have fewer muscles, some of those enumerated being sup*

52 THE ANATOMY OF VERTEBRATED ANIMALS.

pressed. What are ofteo regarded as muscles special to man,
such as the extensor proprius hidicis and extensor minimi
diglti^ are only remains of muscles which are more fully de-
veloped in lower mammals, and send tendons to all four of
the ulnar digits.

Only the pollex has an opponens.^ Only the pollex and
hallux have adductors and abductors. Some of the dioits
lack one or more of the ventral, or of the dorsal, muscles.

The correspondence between the muscles which have been
mentioned, at their insertion in the digits, is clear enough,
but some difficulties present themselves when the muscles are
traced to their origins.

In Man, the flexors and extensors of the digits (except the
interossei) of the fore-limb arise in part from the humerus,
and in part from the bones of the forearm, but not within the
manus. On the contrary, none of the flexors and extensors
of the digits of the pes arise from the femur, while some of
them arise within the pes itself. The origins of the muscles
seem to be, as it were, higher up in the fore-limb than in the
hind-limb. Nevertheless, several of the muscles corresj)ond
very closely. Thus, on the dorsal aspect, the extensor ossis
m,etacar2n polUcis passes from the post-axial side of the proxi-
mal region of the antebrachium obliquely to the trapezium
and the metacarpal of the pollex, just as its homologue, the
tibialis anticus, passes from the post-axial side of the upper
part of the leg to the entocuneiform and the base of the me-
tatarsal of the hallux ; the two muscles correspond exactly.
But the extensors of the phalanges of the pollex, and the deep
extensors of the other digits of the manus, arise on the same
side of the antebrachium, below the extensor ossis metacarpi
pollicis y while, in the leg, one of the deep extensors of the
hallux, and all those of the other digits, arise still lower
down, viz., from the calcaneum.

Not less remarkable is tlie contrast between the more
superficial sets of extensors in the two limbs. In the fore
limb, proceeding from the pre-axial to the post-axial side, the
following extensor muscles arise from the external or pre-
axial condyle of the humerus : the extensor carpi radicdis lon-
gus to the base of the second metacarpal ; the extensor carpi
radialis brevis to the base of the third metacarpal ; the exten-
sor communis digitorum to the four ulnar digits ; the exte?i'
sor minimi digiti to the fifth digit ; the extensor carpi ul

* I have seen an opponens in the hallux of an Orang.

THE MUSCLES OF THE LIMBS. 53

naris to tlie base of the fifth metacarpal. In tlie hind-limb,
fchere are no homologues of the first two of these muscles.
The homologue of the extensor communis is the long extensor,
which arises, not from the femur, but from the fibula. The
2')eronceics tertlus^^ passing from the dorsal face of the fibula
to the fifth metatarsal, is the only representative of the exten-
sor carpi uhiaris.

On the ventral aspect of the human fore-limb, two deej^
flexors arise from the radius, ulna, and interosseous membrane,
and run parallel with one another, thoug-h disconnected, to
the digits. These are, on the pre-axial side — t\iQ flexor p)olli-
cis longus^ to the distal phalanx of the pollex ; and t\\e flexor
iUgitorum perforans^ to the distal phalanges of the other
diOTts.

In the hind-limb, two homologous muscles, ^q flexor hair
lucis longus and the flexor digitorum perforans^ arise from
the tibia and fibula and interosseous membrane, and their ten-
dons are distributed to the distal phalanges of the digits.
But, before they divide, the tendons become connected to-
gether in such a way that many of the digits receive tendi-
nous fibres from both sources.

In the fore-limb, there are no other deep flexors, but the
internal, or post-axial, condyle of the humerus gives origin to
a number of muscles. These, proceeding from the pre-axial
to the post-axial side, are Wiq flexor carpi radialis to the base
of the second metacarpal ; the palmaris longus to the fascia
of the palm; \\iQ flexor per for atus digitorum to the middle
phalanges of the four ulnar digits ; \hQ flexor carpi idnaris to
the base of the fifth metacarpal. The sesamoid, pisiform bone
is developed in the tendon of the last muscle.

The only muscle which exactly corresponds with any of
these, in the hind-limb, is the p>lantaris j which, in Man, is a
slender and insignificant muscle proceeding from the outer
(post-axial) condyle of the femur to the plantar fascia — and
answers to the pcdmaris longus. In many quadrupeds, as the
Rabbit and Pig, the plantaris is a large muscle, the tendon
of which passes over the end of the calcaneal process en-
sheathed in the tendo achilUs^ and divides into slips, which
become the perforated tendons of more or fewer of the digits.

* This muscle, which lies altogether on the dorsal face of the hind-limb,
find which I have seen only in Man, should not be confounded, as it often is,
with one or more muscles, the peroncei Stii, 4.ti, et bti digiti. which are very
often developed in other Mammalia^ but arise on the ventral face of the fibula,
Rnd send their tendons below the external malleolus to the extensor sheatha
of the fifth, -^^urth and even third di^jits.

54 TEE ANATOMY OF YERTEBKATED ANIMALS.

The flexor carpi racUalis is also roughly represented by the
tibialis posticus — a muscle which passes from the tibia and
interosseous membrane to the entocuneiform, and therefore
differs in insertion, as well as in origin, from its analogue in
the fore-limb. The flexor perforatus digitorum of the foot
takes its origin sometimes from the calcaneum ; sometimes, in
part from the calcaneum, and in part from the perforating
flexor ; or it maybe closely connected with the tendons of the
p)lantaris. T\\e p)eronce%is hrems represents the ^ea^or carp>%
ixlnaris by its insertion, but it arises no higher than the fibula,
and has no sesamoid.

Two most important muscles 3^et remain to be considered
in the leg. The one of these is that which is inserted by the
tendo achillis into the calcaneum, and arises by four heads,
two from the condyles of the femur (called gastroc72emius),
and two from the tibia and fibula (called soleus). The other
muscle is the ^^ero^zcpws ^o??^i^5, arising from the fibula, pass-
ing behind the external malleolus, and then crossing the foot
to the base of the metatarsal of the hallux.

The latter muscle does not appear to have any representa-
tive in the fore-limb. The gastrocnemius and salens may pos-
sibly represent the cruj-al part of the perforated flexor, since,
in many of the Vertehrata^ the tendo achillis is but loosely
connected with the calcaneum, and passes over it into the
plantar fascia and the perforated tendons. A peculiar adduc-
tor muscle of the hallux in Man and Apes is the traoisversalis
p)edis^ which is inserted into the basal phalanx of the hallux,
and arises from the distal ends of the metatarsals of the
other digits. The muscle sometimes has an analogue in the
manus.

Electrical Organs. — Certain fishes belonging to the gen-
era Torpedo (among the Elasmohranchii)^ Gynmotus, Ma-
laptemriis^ and Mormyrus (among the Teleostei)^ posses
organs which convert nervous energy into electricity, just as
muscles convert the same energy into ordinary motion, and
therefore may well be mentioned in connection with the ner-
vous system. The " electrical organ " is alwaj's composed of
nearly parallel lamellag of connective tissue, enclosing small
chambers, in which lie what are termed the electriccd ptlates.
Tliese are cellular structures, in one face of which the final
ramifications of the nerves, which are supplied to the organ
by one or many trunks, are distributed. The face on which
the nerves ramify is in all the plates the same, being inferior
in Torpedo^ where the lamellae are disposed parallel to the

THE ELECTRICAL ORGANS.

55

upper and under surHices of the body ; posterior in Gymno-
tus, and anterior in JIalapterurus, the lamellae being disposed
perpendicularly to the axis in these two fishes. And this sur-
face, when the discharge takes place, is always negative to
the other.

ii f.l»'.^r,',^^,r-:_^ »,

Fig, 18.— The Torpedo, with its electrical apparatus displayed. — &, branchia>; c, brain; e,
electric organ ; ^, cranium; 7ne, spinal cord; «, nerves to the pectoral lins ; nl, nervl
later ales ; np, branches of the pneumogasti-ic nei-ves going to the electric organ ; o,
eye.

Ill Torpedo the nerves of the electrical organs proceed
from the fifth pair, and from the " electric lobe " of the
medulla oblongata^ which appears to be developed at the
origin of the pneumogastrics. In the other electrical fishes
the organs are supplied by spinal nerves ; and, in Mala/pter
ruTUS, the nerve consists of a single gigantic primitive fibre,
which subdivides in the electrical organ.

The ordinary Rays possess organs of much the same
structure as the electrical apparatus, at the sides of the tail.

The JVervoiis System: the JEJncejjhalon. -^In. all vcrte-
brated animals except A.m2:)hioxus, the brain exhibits that
separation into & J'ore-brain,7nid-brain, and hlnd-hraiyi^ which

56

THE AXATOMY OF YERTEBRATED ANIMALS.

results from its embryonic division, by two constrictions, into
the three thin-walled vesicles — the anterior, middle, and pos-
terior cerebral vesicles — already mentioned. The cavities of
these vesicles — the primitive ventricles of the brain — freely
communicate at first, but become gradually diminished by the
thickenino^ of their sides and floors. The cavitv of the ante-
rior vesicle is, in tlie adult human brain, represented by the
so-called third ventricle ^ that of the middle vesicle, by the
iter a tertlo ad quartuni ventriculum y that of the posterior
vesicle, by the fourth ventricle.

The floor and sides of the posterior vesicle, in fact, thicken
and become the medulla oblongata ^ together with the pons
varolii^ in those animals which possess the latter structure.

FW.

FitJ. 19. — Diajrrainmatic horizontal section of a Vertebrate brain. The tollowinfir letters
serve for both this figure and Fig. 20: 3Ib, Mid-brain. What lies in front of this is the
fore-brain, and what Ues behind, the hind-brain. L. ^., the lamina terminalis; Olf. the
olfactory lobes ; limp, the hemispheres ; Tli. E, the thalamencephalon ; Pn, the pineal
P'land; P.y, the pituitary body; FM, the foramen of Munro; Ci', the corpus striatum;
7"A, the optic thalamus; CQ. the corpora quadriiremina; CC the crura cerebri; C6. the
cerebellum; /T, the pons varolii; ^1/6*, the medulla oblongata ; /, olfactorii ; //, optici;
///, point of exit from the brain of the motores oculorum ; /F, of the pathetici ; F7, of
the abducentes; F-X/7, origins of the other cerebral nerves. 1, olfactory ventricle;
2, lateral ventricle; 3, third ventricle; 4, fourth ventricle ; +, iter a tertio dd quavtum
r,e,ntHculum.

THE EXCEniALON.

61

riie posterior part of the roof is not converted into nervous
matter, but remains thin and attenuated ; the ejje?idy7na, or
lining of the cerebral cavity, and the arachnoid^ or serous
membrane v,'hich covers the brain externally, coming- nearly
into contact, and forming', to all appearance, a single thin
membrane, which tears with great readiness, and lays open
the cavity of the fourth ventricle. Anteriorly, on the other
hand, the roof becomes converted into nervous matter, and
may enlarge into a complex mass, which overhangs the
posterior division, and is called the cerebellum. The j90??s
varolii^ when it exists, is the expression of commissural fibres,
which are developed in the sides and floor of the anterior part
of the posterior cerebral vesicle, and connect one half of the
cerebellum with the other.

Thus, the hind-brain differs from the posterior cerebral
vesicle in being differentiated into the medulla oblongata (or
inyelencephcdon) behind, and the cerebellum wdth the pons
varolii (which together constitute the metenceplialori) in
fi-ont.

The floor of the middle cerebral vesicle thickens and
becomes converted into two great bundles of longitudinal
fibres, the crura cerebri. Its roof, divided into two, or four,
convexities by a single longitudinal, or a crucial, depression,
is converted into the " optic lobes," corpora bigemina or
quadrigemina. And these parts, the optic lobes, the crura
cerebri, and the interposed cavity, which either retains the
form of a ventricle, or is reduced to a mere canal (the iter a

Pit.

M.li.

xsr

v-^sr

Vio. 20. — A longitudinal and vertical section of a Vertebrate brain. — The letters as before.
The lamina teiininaiis is represented by the strong black line between FM and 3.

iertlo ad quartum ventricidwn)^ are the components of the
mid-brain or Tnesencej^halon.

The anterior cerebral vesicle undergoes much greater

58 THE ANATOMY OF VERTEBRATED AXIMALS.

changes tlian either of the foregoing ; for, in the first place,
it throws out from its anterior lateral parietes two hollow
prolongations, the hemispheres (or prosencephala)^ and each
of these again protrudes from its anterior end a smaller
hollow process, the olfactory lohe (or rhinencephalon). By
the development of these processes the anterior vesicle
becomes divided into five parts — one median and posterior,
and four anterior and paired. The median and posterior,
which remains as the representative of the greater part of
the original anterior cerebral vesicle, is the vesicle of the third
ventricle (or thalamencephalon). Its floor is produced into a
conical process, the infundibulwn^ the blind end of which is
connected with the pituitary body, or hypophysis cerebri. Its
sides thicken greatly, acquire a ganglionic structure, and
become the optic thalarni. Its roof, on the other hand,
resembles that of the fourth ventricle, in remaining very thin,
and, indeed, a mere membrane. The pineal gland, or epiphy-
sis cerebri^ is developed in connection with the upper wall of
the third ventricle ; and, at the sides of its roof, are two ner-
vous bands, which run to the pineal gland, and are called its
peduncles.

The front wall of the vesicle, in part, becomes the so-called
lamina terminalis, which is the delicate anterior boundary of
the third ventricle. In certain directions, however, it thickens
and gives rise to three sets of fibres, one transverse and two
vertical — the former lying in front of the latter. The trans-
verse fibres pass on either side into the corpora striata, and
constitute the anterior commissure which connects those bodies.
The vertical fibres are the anterior pillars of the fornix, and
they pass below into the floor of the third ventricle, and
into the corpora mammillaria, when those structures are de-
veloped.

The outer and under wall of each cerebral hemisphere
thickens and becomes the corpus striatum^ a ganglionic struct-
ure which, from its origin, necessarily abuts against the outer
and interior part of the oj^tic thalamus. The line of demar-
cation between the two corresponds with the lower lip {taenia
semicircularis) of the aperture of communication (called the
foramen of 3Iunro) between the third ventricle and the
cavity of the cerebral hemisphere, which is now termed the
lateral ventricle. In the higher Vertebrata, the upper lip of
the foramen of Munro thickens, and becomes converted into a
bundle of longitudinal fibres, which is continuous, anteriorly,
with the anterior pillars ot the fornix before mentioned. Pos-

THE MODIFICATION OF TUE liRAIN. 59

'^eriorly, these longitudinal fibres are continued backward and
downward along the inner wall of the cerebral hemisphere,
following the juncti(^n of the corpora striata and optic thalami,
and pass into a thickening of the wall of the hemisphere,
which projects into the lateral ventricle, and is called the
lilppocampus major. Thus a longitudinal commissural band
of nervous fibres, extending from the floor of the third ven-
tricle to that of the lateral ventricle, and arching over the fora-
men of Munro, is produced. The fibres of opposite sides unite
over the roof of the third ventricle, and constitute what is
called the body of the fornix. Behind this union the bands
receive the name oi \)i\Q posterior pillars of the fornix.

The optic thalami may be connected by a gray soft com-
missure / and a posterior comtnissure, consisting of transverse
nerve-fibres, is generally developed between the posterior ends
of the two thalami.

In the Mamynalia^ a structure, which is absent in othef
Vertehrata, makes its appearance ; and, in the higher members
of that class, this corpus calloswn is the greatest and most im-
portant mass of commissural fibres. It is a series of trans-
verse fibres, which extends from the roof of one lateral ventr-
cle to that of the other, across the interval which separates
the inner wall of one hemisphere from that of the other.

When the corpus callosum is largely developed, its ante-
rior part crosses the interspace between the hemispheres con-
siderably above the level of the fornix ; so that between the
fornix and it, a certain portion of the inner wall of each
hemisphere, with the intervening space, is intercepted. The
portion of the two inner walls and their interspace, thus
isolated from the rest, constitutes the septum lucidicra^ mth
its contained fifth ventricle.

The Modifications of the Brain. — The chief modifications
in the general form of the brain arise from the development
of the hemispheres relatively to the other parts. In the lower
vertebrates the hemispheres remain small, or of so moderate a
size as not to hide, by overlapping, the other divisions of the
brain. But, in the higher 3Iarnrnalia, they extend forward
over the olfactory lobes, and backward over the optic lobes
an i cerebellum, so as completely to cover these parts ; and, in
addition, they are enlarged downward toward the base of the
brain. The cerebral hemisphere is thus, as it were, bent round
its corpus striatum^ and it becomes distinguished into regions,
or lohes^ which are not separated by any very sharp lines of
demarcation. These regions are named the frontal^ parietal^

60 THE ANATOMY OJ VERTEBRATED ANIMALS.

occipital, and temporal lobes — while, on the outer side of the
corpus striatum, a central lobe (the insula of Reil) lies in
the midst of these. The lateral yentricles are prolonged
into the frontal, occipital, and temporal lobes, and acquire
what are termed their anterior, pjosterior^ and descendiyig
cornua.

Furthermore, while, in the lower vertebrates, the surface
of the cerebral hemispheres is smooth ; in the higher, it be-
comes complicated by ridges and furrows, the gyri and sulci^
which follow particular patterns. The superficial vascular lay-
er of connective tissue which covers the brain, and is called
pia mater, dips into these sulci : but the arachnoid, or delicate
serous membrane, which, on the one hand, covers the brain,
and, on the other, lines the cranium, passes from convolution
to convolution without entering the sulci. The dense perios-
teal membrane which lines the interior of the skull, and is
itself lined by the parietal layer of the arachnoid, goes by the
name of the dura mater.

The general nature of the modifications observable in the
brain as we pass from the lower to the higher mammalia is
very well shown by the accompanying figures of the brain of
a Rabbit, a Pig, and a Chimpanzee (Figs. 21 and 22).

In the Rabbit, the cerebral hemispheres leave the cerebel-
lum completely exposed when the brain is viewed from above.
There is but a mere rudiment of the Sylvian fissure at Sy, and
the three principal lobes, frontal {A), occipital {JB), and tem-
poral ( G), are only indicated. The olfactory nerves are enor-
mous, and pass by a broad smooth tract, which occupies a
great space in the lateral aspect of the brain, into the natiform
protuberance of the temporal lobe ( C).

In the Pig, the olfactory nerves and tract are hardly less
conspicuous ; but the natiform protuberance is more sharply
notched off, and begins to resemble the unciform gjTus in the
higher 3Iammalia, of which it is the homologue. The tem-
poral gyri ( C), though still very small, begin to enlarge down-
ward and forward over this. The upper part of the cerebral
hemisphere is much enlarged, not only in the frontal, but also
in the occipital region, and to a great extent hides the cere-
helium when the brain is viewed from above. What in the
\labbit was a mere angulation at Sy, in the Pig has become a
.ong sulcus — the Sylvian fissure, the lips of which are formed
by a gyrus, the Sylvian, or angidar, gyrus. Two other sets
of gyri, more or less parallel with this, are visible upon the
outer surface of the hemisphere; and at the entrance of the

THE MODIFICATION OF THE BRAIN.

6]

LOc.

ri3. 21.— Lateral views of the 'brams of a Eabbit, a Pig, and a Chimpanzee, drawn of nearly
the same absolute size. The Eabbif s brain is at the top ; the Pig's, in the middle, the
Chimpanzee's, lowest.— 0^, the olfactory lobe; ^., the frontal lobe; B.^ the occipital
lobe; C, the temporal lobe; *??/., the Sylvian fissure; /«., the insula; S.Or., sui.ra-
orbital ; 8.F.^ M.F.^ I.F., superior, middle, and inferior frontal gyri ; A.P., antero-pari-
etal; P.P., postero-parietal gyri; R, sulcus of Rolando; P.Pl, postero-parietal lobule ;
(?.P/., external perpendicular or occipito-temporal sulcus; ^7i, angular gyrus ; 2,3,4,
annectent gyri; A.T., M.T., P.T., the three temporal, and S.Oc, M.Og., LOc., the threa
ot'^ipitiil gyri.

62 THE ANATOMY OF VERTEBRATED AKDIALS.

Sylvian fissure, at In^ there is an elevation wliicli answers to
the insula., or central lobe.

In the Chimpanzee, the olfactory nerves, or rather lobes,
are, relatively, very small, and the tracts which connect them
with the uncinate gyri {suhstantm perforatiGe) are comjoletely
hidden by the temporal gyri ( C^\ The Sylvian fissure is very
long and deep, and begins to hide the insula., on which a few
fan-shaped gyri are developed. The frontal lobes are very
large, and overlap the olfactory nerves for a long distance ;
while the occipital lobes completely cover and extend beyond
the cerebellum, so as to hide it completely from an eye placed
above. The gyri and sulci have now attained an arrangement
which is characteristic of all the highest Mainrnalia. The
fissure of Rolando {It) divides the antero-parietal gyrus i^A. P)
from the postero-parietal (P.P). These two gyri, with the
postero-parietal lobule {P.PL), and part of the angular gyrus
(A7i)j constitute the I*arietal lobe. The frontal lobe, which
lies anterior to this, the occipital lobe, which lies behind it,
and the temporal lobe, v/hich lies below it, each present three
tiers of gyri, which, in the case of the frontal and occij^ital
lobes, are called superior, middle, and inferior — in that of the
temporal lobe, anterior, middle, and posterior. The inferior
surface of the frontal lobe, which lies on the roof of the orbit
(xS. Or?)., presents many small sulci and gyri.
^ On the inner face of the cerebral hemisphere (Fig. 22) the
o^ sulcus presented by the Rabbit's brain is that deep and
broad depression (jK) which runs parallel with the posterior
pillar of the fornix, and gives rise, in the interior of the de-
scending cornu of the lateral ventricle, to the projection which
is termed the hippocampus major. In the Pig, this hippocam-
pal sulcus {PT) is much narrower and less conspicuous ; and a
marginal (ilT) and a colossal ( C) gyrus are separated by a
well-marked calloso-marginal sulcus. As in the Rabbit, the
uncinate gyrus forms the inferior boundary of the hemisphere.
In the Chimpanzee, the marginal and callosal gyri are still
better marked. There is a deep internal perpendicular, or
occipito-parietal., sulcus [P.]^, The calcarine sulcus {Ca)
causes a projection into the floor of the posterior cornu,
which is the hijyj^ocam pus minor ^ while the collateral sulcus
(Coll) gives rise to the eminence of that name in both the
posterior and descer^dmg cornua. The hippocampal sulcus
{S^ is relatively insignificant, and the lower edge of the tem-
poral lobe is formed b}'' the posterior temporal g}Tus.

In tlie Rabbit, the corpus callosum is relatively small, much

THE MODIFICATION OF THE BKAIN.

63

Pl3. 22. — Inner views of the cerrbral hemispheres of the Eabbit, Pig', and Chimpanzee,
drawn as before, and placed in the same order. 01., olfactory lobe ; C.c, corpus callo-
sum; A.c. anterior commissure; R., hippocampal sulcus; C^n., uncinate ; M.. mar-
ginal ; (\. callosal gyri ; I.p., internal perpenuicular ; Ca., calcarine ; Coll., collateral
sulci; F , fornix.

inclined upward and backward ; and its anterior extremity is
but slightly bent downward, so that the so-called ge7iu and
rostrum are inconspicuous. The Pig's corpus callosum ia

64 THE ANATOMY OF YERTEBRATED ANIMALS.

larger, more horizontal, and possesses more of a rostrum in
the Cliimpanzee, it is still larger, somewhat defiexed, and very
thick posteriorly ; and has a large rostrum. In proportion to
the hemispheres, the anterior commissure is largest in the
Rabbit and smallest in the Chimpanzee. The Rabbit and the
Pig have a single corpus inanimiUare, the Chimpanzee has
two. The cerebellum of the Rabbit is very large in proportion
to the hemispheres, and is left completely uncovered by them
in the dorsal view. Its median division, or vermis^ is straight,
symmetrical, and large in proportion to the lateral lobes. The
floecull^ or accessory lobules developed from the latter, are
large, and project far beyond the margins of the lateral lobes.
The ventral face of the metencephalon presents on each side,
behind the posterior margin of the pons varolii, flattened rec-
tangular areae, the so-called corpora trapezoiclea.

In the Pig, the cerebellum is relatively smaller, and is par-
tially covered by the hemispheres ; the lateral lobes are larger
in proportion to the vermis and the flocculi, and extend over
the latter. The corpora trapezoidea are smaller. In the Chhn-
panzee, the relatively still smaller cerebellum is completely
covered ; the vermis is Yery small in relation to the lateral
lobes, which cover and hide the insignificant flocculi. There
are no corpora trapezoidea.

In all the characters now mentioned, the brain of Man
diS'ers far less from that of the Chimpanzee than that of the
latter does from the Pig's brain.

The JSfyelon. — The spinal canal, and the cord which it con-
tains, are lined by continuations of the three membranes which
protect the encephalon. The cord is sub-cylindrical, and con-
tains a median longitudinal canal, the canalis centralis^ the
remains of the primitive groove. It is divided by anterior and
posterior median fissures into two lateral halves, Avhich are,
usually, connected only by the comparatively narrow isthmus,
which immediately surrounds the canalis centralis. The cord
may, in the adult, extend through the whole spinal canal, or it
may come to an end at any point between the caudal extrem-
ity and the anterior thoracic region.

The distribution of the two essential constituents of ner-
rous tissue, ganglionic corpuscles and nerve-fibres, is very defi-
nite in the spinal cord, ganglionic corpuscles being confined
to the so-called " gray matter " which constitutes the isthmus,
and spreads out into two masses, each of which ends in an an-
terior (or ventral) and a posterior (or dorsal) horn. Nerve-

THE MYELON.

06

Fig 23. — A diagrammatic view of the Chief Trunks of the Cerebro-spinal and Sympathetic
Nervous Systems of Rana esculeriia seen from below Ct^A'ice the size of nature). — I. The
olfactory nerves. N. The olfactory sac. II. The optic nerve. 0. The eye. Z. op.
The optic lobes. Ta. Optic tracts passing from the optic lobes to the chiasma. behind
which lies the pituitary body. III. Ociilomotovius. IV. Patheticus. Y The tri-
g'eminal, with which the abducens (Yl.), facialis (VII.). and the upper end of the sym-
pathetic (Fas'.), are closely connected. Branches of this nervous plexus are V.a. the
nasal and ophthalmic branches of the fifth and the alxJiicens. V, b, c, d. the palatine,
maxillary, and mandibular branches of the fifth. V, e, the tympanic branch into which
the proper facial nerve (VII.) enters, and, with a branch of the vagus, forms the so-
caUed facial nerve of the Frog. F. VIII. The auditory nerve. X, ^vith its branches
Jfi, X^, A'3, X*, represents the glossophaiyngeal and the vagus. The medulla (il>
longata {Myelence]>halon) ends, and the medulla spinalis {Myelon) begins, about tlie
region marked by the letter J/. J/ 1-10, the spinal nerves. 3/2, the brachial nerves,
31 7, 8, 9, the ischiatic plexus, from which proceed the crural (N. c.) and ischiatic (N. i.)
nerves. S. The trimk of the sympathetic. S.M. The commimicating branches Avitb
Uie spinal ganglia. S 1-10. The"symp;it±ieti£ canclia.

66 THE AXATOMY OF VERTEBRATED ANIMALS.

fibres also abound in the gray matter ; but the so-called " white '
matter," which constitutes the external substance of the cord,
contains only the fibrous nervous matter, and has no gangli-
onic corpuscles.

The spinal nerves arise in opposite pairs from the two
halves of the cord, and usually correspond in number with the
vertebrae through, or between, which they pass out (Fig. 23),
Each nerve has two roots, one from the dorsal, and one from
the rentral, reo^ion of its half of the cord. The former root
has a ganglionic enlargement, and only contains sensory
fibres ; tlie latter has no ganglion, and exclusively contains
motor fibres.* After leaving the vertebral canal, each spinal
nerve usually divides into a dorsal and a ventral branch ; but,
in the Ganoid fishes, each of these branches is a distinct nerve,
arising by its owm proper roots.

The Cerebral Nerves. — The greatest number of pairs of
nerves ever given off from the vertebrate brain is twelve, in-
cluding the so-called olfactory nerves, and the optic nerves,
which, as has been seen, are more properly diverticula of the
brain, than nerves in the proper sense of the word.

The olfactory " nerves " (olfactorii) constitute the Jirst
pair of cerebral -nerves. They always retain their primary
connection with the cerebral hemispheres, and frequently con-
tain, throughout life, a cavity, the olfactory ventricle, which
communicates with the lateral ventricle.

The optic " nerves " {pptici) are the second pair of cere-
bral nerves. In the Lampreys and Hags [Marsip>ohranchli)
these nerves retain their embryonic origin from the thalam-
encephalon, and each goes to the eye of its own side. In
other Vertebrata, the nerves cross one another at the base of
the brain (Teleostei), or are fused together into a cliiasma
[Ganoidei, Elasmobranchii, and all the higher Verteb7X(ta).
In the higher Vertebrata, again, the fibres of the optic nerves
become connected chiefly with the mesencephalon.

All the other cerebral nerves difi'er from these in arising,
not as diverticula of any of the cerebral vesicles, but by histo-
logical differentiation of the primitive brain-case, or laniincB
dorsales of the skull.

The third (motores oculorum) and foui'th [2K(fheti':'i) pairs
of nerves are distributed to the muscles of the eye ; the third
to the majority of these muscles, the fourth to the superior

♦ Amphioxm appears to be an exception to this, as to most ot.her, rules of
Vertebrate anatomv.

THE CEREBRAL NERVES. 07

oblique muscles. The third pair of iierv^es issues from the
crura cerebri, or inferior division of the metencephalon, upon
the base of the brain ; the fourth pair, from the fore-part of
the upper division of the metencephalon, immediately be-
hind the optic lobes, upon the superior surface of the brain.
This region is known as the Vcclve of Vieussens in the Mam-
malia.

All the other cerebral nerves originate in the posterior di-
vision of the hind-brain — the myelencephalon. The great
fifth pair {trigemini) passes out from the sides of the meten-
cephalon, and supplies sensory nerves to the integument of
the head, and motor nerves to most of the muscles of the
jaws, by its three divisions — the ophthalmic^ the superior
maxillary^ and the inferior maxillary^ nerves.

Of these divisions the two latter are, very generally, closely
connected together, while the ophthalmic division remains
distinct. The ophthalmic division passes to the cleft between
the trabecula and the maxillary process (which nearly corre-
sponds with the orbit, and might be termed the 07'hito-nasal
cleft), and is distributed to the inner and the outer side of that
cleft. Hence its main branches are nasal and lachrymal. The
two maxillary nerves, on the other hand, are distributed to the
inner and outer sides, or anterior and posterior boundaries, of
the buccal cleft. Hence the superior maxillary belongs to the
posterior, or outer, side of the maxillary process, while the in-
ferior maxillary appertains to the anterior region of the first
visceral arch. The superior maxillary commonly unites with
the outer, or lachrymal, division of the ophthalmic ; the in-
ferior maxillary with the anterior division of the facial.

In the higher Vertebrata^ the trigeminal nerve usually ha?
two very distinct roots, a dorsal sensory, pro\dded with a gan
glion (the Casserian ganglion), and a ventral motor, non-gan-
glionated. The fibres of the latter pass almost exclusively into
the inferior maxillary division. In addition, the ophthalmic
division may have a ganglion {ciliary) ; the superior maxillary
another [sphenopalatine or Mechelian)^ and the inferior maxil-
lary a third {otic).

The sixth pair {abducentes) issues from the inferior surface
of the brain, at the junction of the myelencephalon with the
metencephalon. It supphes the external straight muscles of
the eye ; with the muscles of the nictitating membrane, and
the retractor bulbi^ or musculus choanoides^ when such mus-
cles exist.

The seventh pair {faciale^) supplies the superficial facial

58 THE ANATOMY OF YERTEBRATED ANIMALS.

muscles, and ultimately divides into two branches, one of
which is in relation with the mandibular, and the other with
the hyoidean arch.

The five nerves which have just been mentioned are often
intimately connected together. Thus, in the Lepidosiren^ the
three motor nerves of the eyeball are completely fused with
the ophthalmic division of the fifth.* In the j\fyxinoid fishes
there are no motor nerves of the eyeball ; but, in the Lampre}',
the rectus externus and inferior^ and the ohllquus inferior^ are
supplied by the ophthalmic, while the oculomotor and the pa-
thetic unite into a common trunk, which gives branches to the
rectus superior and internus^ and ohllquus superior. The ocu-
lomotor, the pathetic, and the abducens, are more or less con-
founded with the ophthalmic in the Amphibia ; but in Tele-
ostei^ Ganoidei^ Elasraobranchii^ and in all the higher Verte-
brata^ the nerves of the muscles of the eye are distinct from
the fifth pair, except where the oculomotor unites with the
ophthalmic into the ciliary ganglion.

The facial and the trigeminal nerves have common roots
in fishes. In Amp)hihia, though the roots are distinct, the
facial may be completely united with the ganglion of the tri-
geminal, as in the Frog. In all abranchiate Vertebrata the
two nerves are quite distinct.

Whether the nerves are distinct or not, 2, pcdatine^ or vidi-
an^ nerve (which, in the higher Vertebrata^ is especially con-
nected with the facial), runs through, or beneath, the base of
the skull, parallel with its long axis ; and, after uniting with
the superior maxillary, and usually contributing to form the
sphenopalatine^ or Mechelian^ ganglion, is distributed to the
mucous membrane of the roof of the mouth ; and the mandib-
ular division of the seventh, or chorda tympani^ unites v/ith
the inferior maxillary division of the fifth nerve.

The eighth pair \auditorii) is formed by, the nerves of the
org-an of hearing^.

The ninth pair [r/lossopharyngei) is especially distributed to
the pharjmgeal and lingual regions of the alimentary canal,
and, primarily, supphes the boundaries of the second visceral
cleft.

The tenth pair {pneumogastricl or vagi) consists of vcrj

*I am ofreatly disposed to think that the motor nerves of the eye more
nearly retain their primary relations in Lepidosiren than in any other verte-
brated animal ; and that they are really the motor portions of the nerves of
the orbito-nasal cleft, the third and fourth appertaining to the inner division
of the ophthalmic, the sixth to its outer division.

THE EXITS OF THE CEREBRAL NERVES. 69

remarkable nerves, wliicli pass to the gullet and stomach, the
respiratory and vocal organs, to some parts of the integument
of the body, and to the heart. In the Ichtliyopsida they give
oiT, in addition, long lateral nerves to the integuments of the
sides of the body. In the higher Yertebrata^ these lateral
nerves are represented only by small branches distributed
chiefly to the occipital region. The ninth and tenth pairs are
both motor and sensory in function, and are often so inti-
mately connected as to form almost one nerve.

The eleventh pair (accessorii) are cerebral only by courtesy,
as these nerves take their origin from the spinal cord, by
roots which issue between the proper anterior and posterior
roots of the spinal nerves, and, joining together, form, on
each side, a nerve which passes out with the pneumogastric,
partly joining it, and partly going to muscles which arise from
the head and anterior vertebrae, and are inserted into the pec-
toral arch.

The spinal accessory exists in no Ichthyopsid vertebrate,
but is found in all Saurojysida^ with the exception of the
Ophidia^ and in the Maminalia.

The twelfth and last pair {Jiypoglossi) are the motor nerves
of the tongue, and of some retractor muscles of the hyoidean
apparatus.

In the Ichtliyopsida the first cervical nerve supplies the
distributional area of the hypoglossal ; but in all the abran-
chiate Yertebrata there is a hypoglossal, which traverses a
foramen in the ex-occipital, though it oftens remains closely
connected with the first cervical, and may rather be regarded
as a subdivision of that nerve, than as a proper cerebral
nerve.

Thus the nerves arising from the hind-brain, in all the
higher Yertehrata, fall into three groups : 1st, a sensori-motor,
pre-auditory, set (3d, 4th, 5th, 6th, 7th) ; 2d, the purely sen-
sory auditory nerve (8th) ; 3d, the sensori-motor, post-audi-
tory, set (9th, 10th, 12th).

The apertures by which several of these nerves leave the
skull, retain a very constant relation to certain elements of
the cranium on each side. Thus :

a. The filaments of the olfactory nerve always leave the
crauium between the lamina perpendicularis, or body of the
ethmoid, and its lateral or prefrontal portion.

b. The optic nerve constantly passes out behind the cen-
tre of the orbitosphenoid and in front of that of the alisphc
uoid.

70 THE ANATOMY OF YERTEBRATED AXDIALS.

c. The third division of the trigeminal, or fifth nerve, al-
ways leaves the skull behind the centre of the alisphenoid and
in front of the prootic.

d. The glossopharyngeal and pneumogastric always make
their exit behind the centre of the opisthotic, and in front of
the centre of the ex-occipital.

The apertures for the exit of the cranial nerves denoted
in the paragraphs a, J, c, c?, when surrounded by bone, and
well defined, are called respectively : a, the olfactory formnen ;
b, the optic foramen ; c, \\\^ foramen on ale ; d^ the foramen
lacerum poster ius. The adjacent bones may take equal shares
in bounding these foramina, or the foramina may be alto-
gether in one bone; but their positions, as here defined, never
cbanw-e.

Another point to be especially considered respecting the
general disposition of the cranial nerves, is the relation which
some of them bear to the visceral arches and clefts, and which
has already been incidentally mentioned. Thus, the seventli
nerve is distributed to the posterior part of the first visceral
arch, and to the anterior part of the second visceral arch, its
two branches enclosino- the first visceral cleft. In like man-

CD

ner, the ninth (glossopharyngeal) nerve is distributed to the
hinder part of the second arch and to the front part of the
third, its branches enclosing the second visceral cleft. The
first branch of the pneumogastric has similar relations to the
tliird and fourth arches and to the third cleft ; and, in bran-
chiate Vertehrdta^ the other anterior branches of the pneumo-
gastric are similarly distributed to the successive branchial
arches, the two divisions of each branch enclosing a branchial
cleft.

The second and the third divisions of the trisreminal are
distributed, in an analogous manner, to the anterior region of
the first visceral arch, and to the posterior or outer region of
the maxillo-palatine process — the gape of the mouth repre-
senting a visceral cleft between the two. The inner and outer
portions of the first division of the trigeminal are similarly
related to the inner, or anterior, region of the maxillo-palatinr*
process, and the outer side of the trahecula cranil — the orbito
nasal fissure representing the cleft between the two.

Considerations of this kind sug:2:est that the trabeculas and
the maxillo-palatine processes may represent pre-oral \dsceral
arches, which are bent forward ; and, in the case of the tra-
heculre^ coalesce with one another. Such an hypothesis would
enable us to understand the signification of the naso-palatine

THE SYMPATHETIC NERVES. 71

canal of the Myxinoid fishes, which would be simply the in-
terspace, or passage, between the trabeculae (which must have
origiDally existed if ever they were distinct visceral arches)
not yet tilled up ; and the anomalous process of the roof of the
oral cavity, which extends toward the pituitary body in thei
embryos of the Vertehrata in general, might be regarded as the
remains of this passage.

On this hypothesis, six pair of inferior arches belong to
the skull — namely, the trabecular and maxillo-palatine, in
front of the mouth ; the mandibular, the hj^oidean, and two
others (first and second branchial), behind it. For, as there
are three cranial nerves embracing the first three visceral clefts
which lie behind the mouth, there must be four post-oral, cra-
nial, visceral arches.

Supposing that the occipital segment in the brain-case an-
swers to the hindermost, or second branchial, cranial, visceral
arch, the invariable attachment of the proximal ends of the
mandibular and hyoidean arches to the auditory capsule leads
rne to assign the parietal and the frontal segments to the max-
illo-palatine and trabecular visceral arches. And thus the os-
sifications of the auditory capsule, alone, are left as possible
representatives of the neural arches of the three anterior post-
oral visceral arches.

But these speculations upon the primitive composition of
the skull, however interesting, must not, as yet, be placed
upon the same footing as the doctrine of its segmentation,
which is simply a generalization of anatomical facts.

The Sympathetic. — A Sympathetic Nervous System has
been observed in all the Vertehrata except A.mphioxus and
the MarsipohranQliU. It consists, essentially, of two longi-
tudinal cords, placed one upon each side of the inferior face
of the cranio-spinal axis. Each cord receives communicating
fibres from the spinal nerves of its own side, and, when com-
plete, from all the cranial nerves except those of the special
senses of hearing, sight, and smell — the Vidian nerves consti-
tuting the anterior terminations of the vsympathetic cords. -At
the points of communication ganglia are developed, and the
nerves which emerge from these ganglia are distributed to the
muscles of the heart and vessels, and to those of the viscera.
These peripheral nerves of the sympathetic system frequently
present small ganglionic enlargements.

In the 3Iarsipohranchii^ the place of the sympathetic ap-
pears to be taken, to a great extent, by the pneumogastric j

Y2 THE ANATOMY OF VERTEBRATED ANIMALS.

and, in Myxine^ the two pneumogastrics unite upon the intes-
tine, and follow it, as a single trunk, to the anus.

The Sensory Organs. — The organs of the three higher
senses — Smell, Sight, and Hearing — are situated, as has been'
alreadj'- described, in pairs, upon each side of the skull, in all
vertebrate animals except the lowest fishes ; and, in their
earliest condition, they are alike involutions of the integu-
ment.

The Olfactory A2)pa7'atus acquires no higher complication
than this, being either a single sac {Amjyhioxiis (?) Marsipo-
branchii)^ or, more commonly, two, the surfaces of which are
increased by plaiting, or by the development of turbinal carti-
lages, or bones, from the lateral portions of the ethmoid.
Upon these, nervous filaments arising from the olfactory lobe
of the brain are distributed. The cavities of the olfactory
sacs may be placed in communication with that of the mouth
by the nasal passages ; or, as in the great majority of fishes,
they may have only an external aperture, or apertures.

In Reptiles, Birds, and Mammals, a peculiar nasal gland
is frequently connected with, and pours its secretion into,
each olfactory chamber.

The foramina incisiva, left between the premaxillaries
and the palatine plates of the maxillaries in Mainnialia^ are
sometimes closed by the mucous membranes of the nasal and
oral cavities, and sometimes not. In the latter case they are
the canals qf'Stensoji^ and place these two cavities in com-
munication. Glandular diverticula of the mucous membrane,
supplied with nervous filaments from both the olfactory and
the fifth pair, may open into these canals. Thej^ are called,
after their discoverer, the " organs of Jacohsony

The Eye is formed by the coalescence of two sets of struct-
ures, one furnished by involution of the integument, the other
by an outgrowth of the brain.

The opening of the integumentary depression which is pri-
marily formed on each side of the head in the ocular region
becomes closed, and a shut sac is the result. The outer wall
of this sac becomes the transparent cornea of the eye ; the
epidermis of its floor thickens, and is metamorphosed into the
crystalline lens / the cavitj'' fills with the aqueous humor. A
vascular and muscular ingrowth taking place round the cir-
cumference of the sac, and, dividing its cavity into two seg-
ments, gives rise to the iris. The integument around the cor

THE EYE. 73

nea. frrowins: out into a fold above and below, results in the
formation of the ej-elids, and the segregation of the integu-
ment which they enclose, as the soft and vascular conju7ictiva.
The pouch of the conjunctiva very generally communicates,
by the lachrymal duct^ with the cavity of the nose. It may
be raised, on its inner side, into a broad fold, the nictitating
niemhrane^ moved by a proper muscle or muscles. Special
j'lands -the lachrymal externally, and the Harderian on the
inner side of the eyeball — may be developed in connection
with, and pour their secretion on to, the conjunctival mucous
membrane.

The posterior chamber of the gjq has a totally distinct ori-
gin. Very early, that ])art of the anterior cerebral vesicle
which eventuady becomes the vesicle of the third ventricle,
throws out a diverticulum, broad at its outer, and narrow at
its inner end, which applies itself to the base of the integu-
mentary sac. The posterior, or outer, wall of the diverticulum
then becomes, as it were, thrust in, and forced toward the op-
posite wall, by an ingrowth of the adjacent connective tissue ;
so that the primitive cavity of the diverticulum, which, of
course, communicates freely with that of the anterior cerebral
vesicle, is obliterated. The broad end of the diverticulum ac-
quiring a spheroidal shape, while its pedicle narrows and elon-
gates, the latter becomes the optic nerve, while the former,
surroundino* itself with a strono^ fibrous sclerotic coat, remains
as the posterior chamber of the eye. The double envelope,
resulting from the folding of the wall of the cerebral optic ves-
icle upon itself, gives rise to the retina and the choroid coat:
the plug, or ingrowth of connective tissue, gelatinizes and
passes into the vitreous humor, the cleft by which it entered
becoming obliterated.

Even in the higher Vertehratct the optic nerve is, at first,
connected exclusively with the vesicle of the third ventricle,
and makes no decussation with its fellow. But by degrees
the roots of origin of each nerve extend over to the opposite
side of the brain, and round the thalamus, to the mesencepha-
lon on that side, and the trunks of the two nerves become in-
termixed below the third ventricle, in a close and complicated
manner, to form a chiasma.

In Amphioxus and Myxine, the eyes are very imperfectly
developed, appearing to consist of little more than a rudimen-
tary lens imbedded in the pigment, which encloses the termi-
nation of the optic nerve ; and, in Myxine, this rudimentary eye
is hidden by muscles and integument. It appears doubtful
4

74 THE ANATOMY OF YERTEBRATED ANIMALS.

whether in these fishes, and in the Lampreys, the eye is de
veloped in the same way as in other Vertebrata.

In all other Vertebrata, the eyes have the typical structure,
though sometimes, as in the Blind-fish (Ai^ibl^/opsis) and the
Mole, they have no functional importance. In the Iclithy-
opsida and S>auropsida^ but not in 3Iain)nalia^ the sclerotic
is often partially ossified, the ossification usually forming- a
ring around its anterior moiety. It becomes enormously
thickened in the Cetacea.

Except in Amphioxus and the Myxinoid fishes, the eye-
ball is moved by six muscles ; of these, four, proceeding from
the interior of the orbit to the periphery of the eyeball, and
surrounding the optic nerve, are termed superior, inferior, in-
ternal, and external recti. The other two are connected with
the upper and the lov/er margins of the orbit respectively, and
pass thence to the outer side of the bulb. These are the siipe^
rior and the inferior obliqui. In many Reptiles and Mam-
mals a continuous funnel-shaped sheet of muscle, the muscu-
lus choanoides^ lies within the four recti^ and is attached to
the circumference of the posterior moiety of the ball of the eye.
It would appear, from the distribution of the nerves, which
has already been described, that the rtmseidus cJioanoides^
the external rectus^ and the nictitating muscle, constitute
a group of eye-muscles morphologically distinct from the othei
three o^ecti^ the obliqui^ and the levator palpebrce superioris.
In many Reptiles, and in the higher Vertebrata^ the eyelids
are closed by circular muscular fibres, constituting an orbicvr
laris palpebrarum^ and are separated by straight fibres pro-
ceeding from the back of the orbit, usually to the upper ej'C-
lid only, as the levator palpebrm superioris / but sometimes to
both lids, when the lower muscle is a depressor palpebrm mfe-
rioris.

The Harderian and lachrymal glands are not found in
fishes ; but the former is met with in the JBatrachia, and both
are of common occurrence in the Sauropsida and 3Iammalia.

In Lacertilia, GrocodiHa, Aves, and many Fishes, a pecu-
liar vascular membrane, covered with pigment, like the cho-
roid, projects from near the entrance of the optic nerve, on the
outer side of the globe of the eye, into the vitreous humor,
and usually becomes connected with the capsule of the lens.
This is the p)ecten^ or marsupimn.

TJie Ear. — The first rudiment of the internal ear is an in-
volution of the integument into a small sac, wliich is situated

TUE EAR. 76

on each side of the posterior cerebral vesicle, just above the
end of the second visceral cleft. The mouth of the involution
soon closes, and a shut sac results. The sac enlarges, and, by
a remarkable series of changes, its upper part becomes (ordi-
narily) converted into three seinicircular canals — the anterior
and jjoster lor vertical, and the external or horizontal canals
of the membranous labyrinth. The body of the sac remains,
for the most part, as the vestibule / but a cascal process, which
eventually becomes shut off from the vestibule, is given ofi
downward and inward, toward the base of the skull, and is
the rudiment of the scala media of the cochlea. This may be
called the membranous cochlea.

In the anomalous vertebrate, Am2')hioxus, no ear has yet
been discovered. The Hag (JSIyxvne) has only one, and in the
Lampreys {Petromyzon) there are only two, semicircular ca-
nals ; but, in fishes in general, all three are developed, and it
is a question whether the cochlea is not also represented.

In fishes, the periotic cartilage and its ossifications enclose
this membranous lab3'rinth, externally, and present no merely
membranous gaps, ov fenestrOE, toward the first visceral cleft,
or the space which represents it.

But in higher Vertebrata {Am2:>hibia, Saurojmda, Mam-
malici)^ in which the membranous labyrinth is always enclosed
within a complete bony periotic capsule, the outer wall of
this capsule invariably remains unossified over one or two
small oval areas, Avhich consequently appear like windows w^ith
membranous panes, and are termed the fenestra ovalis and the
fenestra rotunda.

The fenestra ovalis is situated in that part of the periotic
mass which bounds the chamber containing the membranous
vestibule externally ; and it is always found that, when both the
prootic and the opisthotic bones exist, they contribute nearly
equal shares to the formation of its boundaries. In fact, the
fenestra avails is situated in the line of junction of these two
bones. The fenestra rotunda, on the other hand, is below
t\iQ fe7iestra ovalis, and lies altogether in the opisthotic. It
forms part of the outer wall of the cavity in wdiich the mem-
branous cochlea is lodged.

In the Sauropsida and Jfammalia, this membranous coch-
lea, become flattened and bandlike, and its communication
v\'ith the vestibule obliterated, is lodged in a conical cavity, in
such a manner as to divide that cavity into two portion);',
called scalcB, which only communicate at their apices. The
base of the one scala, called sccda vestlbuli, opens into tha

76 THE ANATOMY OF YERTEBRATED ANIMALS.

cavity whicb contains the membranous vestibule : that of the
other, scala tympard^ abuts against, and is as it were stopped
by, the membrane of the fenestra rotunda. The cavity of the
membranous cochlea stretched between, and helj)ing to divide,
these two scalce, is called the scala media.

In Reptiles, Birds, and Ornithodelphous Mammals, the
cochlea is only slightly bent or twisted upon itself. But, in
the higher Mammalia^ it becomes coiled in a flat or conical
spiral of one and a half (^Cetacea, Erinaceus) to five {^Gcelo-
genys Pacd) turns.

The membranous labyrinth is filled with a clear fluid, the
endolymph^ and usually contains otolithes of various kinds.
Between the membranous labyrinth and the walls of the cav-
ity of the periotic mass in which it is contained, lies another
clear fluid, the perilymph^ which extends thence into the scalce
vestihull and tympani.

In all animals which possess a fenestra ovalis, its mem-
brane gives attachment to a disk, whence an ossified rod, or
arch, proceeds. Where the former structure obtains, as in
Birds, most Reptiles, and some Amphibia^ the bone is com-
monly called columella auris ; when the latter, as in most
Mammals, stapes. But there is really no difibrence of impor-
tance between stapes and columella^ and it is advisable to use
the former name for the bone under all its forms.

In the majority oiVertehrata of higher organization than
fishes, the first visceral cleft does not become wholly obliter-
ated, but its upper part remains as a transversely elongated
cavity, by means of which the pharynx would be placed in
communication with the exterior, were it not that the oppo-
site sides of the canal grow together into a membranous par-
tition — the memhrana tympani. So much of the canal as lies
external to this is the external auditory meatus ; while what
lies internal to it, is the tympanum,^ or drum of the ear, and
the Eustachian tube^ which places the tympanum in communi-
cation with the pharynx. While the outer wall of the tym-
panum is the tympanic membrane, its inner wall is the periotic
mass with its fenestrm ; and, in all Vertebrata below Mam-
mals, the outer end of the stapes is either free, or, more com-
monly, is fixed to the tympanic membrane, and thus the latter
and the membrane of \\i<d fenestra ovalis become mechanically
connected. In all these animah the mandible is connected
with the skull by the intermediation of an as quadratum.

But, in the JMammalia^ the mandible is articulated directly
with the squamosal, and the quadratum is converted into one

THE EAR.

11

of the so-called ossicida aicdlMs^ and named the ynaUeus. Tlie
malleus becomes attached to the 'iuemhrana tympani^ by a
special process ; while its other extremity, which was continu-
ous with Meckel's cartilage in the embryo, is converted into
\X\Q, processus gracilis^ or Folianus^ and lies between the tym-
panic, the squamosal, and the periotic bones.

In the singular lizard Sphenodon (A, Fig. 24), the anterior
cornu of the hyoid is continuous with the distal end of the
stapes, and the latter sends a cartilaginous process upward,
which passes into the wall of the periotic capsule, just behind
the proximal end of the os qiiadratum. Thus the stapes
stands out at right angles to the hyoid cornu, and the latter
becomes divisible into a sitpra-stapedlal part, and a part which
lies below the stapes, and answers to the styloid process, or
styloliycd^ of the Mammalia. The supra-stapedial part is rejv
resented by cartilage, or ligament, in other Saurop)sida^ but
seems not to ossify. In the Mammalia (B, Fig. 24), the su-
pra-stapedial part ossifies, becomes the inctis^ and its proximal
end is usually articulated by a sjaiovial joint with the malleus
(= quadratum). A distinct ossification, the os orhiculare^
usually arises at that part of the hyoidean cartilage in which
the stapes and the incus unite. That part of the hj^oidean
cartilage which is converted into the styloid process is gen-
erally connected with the orhicidare by muscular fibres, which
constitute the stapedius rauscle. On the other hand, the pos

SPcSSt^.

^c

s&Er

Fig. 24 — Diagram of the skeleton of the first and second visceral arches in a Lizard (A).

JIammal (B), and an Osseons Fish (C).
The skeleton of the first visceral arch is shaded, that of the second is left nearly nnsrhaded.

/. First visceral arch. 3Tck. Meckel's cartilage. Art. Articulare. Qu. Quadratum.

3rpt, Metapterygoid ; J/. Malleus ; p.g.., Processus gracilis. //. Second viscer."! arch.

Ify. Hyoidean cornu. St. H. Stylohyal. S. Stapedius. Stp. Stapes. S. Htp. &upra-

str.pedial. //J/. liyomandibular. The arrow indicates the fii-st visceral cleft. Pi.. The

periotic capsule. I'tcj. The pterygoid.

terior, or short process of the incus^ is connected by ligament
with that part of the periotic mass into which the styloid pre

78 THE ANATOMY OF YERTEBRATED ANIMALS.

cess is directly continued, and it is liard to say whetlier the
styloid part of the hyoid is continued into the incus by these
ligaments or by the stapedius. But, however this may be, the
inalleus and the incus are the proximal ends of the mandibular
and hyoidean arches respectively.

In osseous fishes (C, Fig. 24), which have no fenestra ova-
lis or stapes, the supra-stapedial part- of the hyoid becomes a
large bone — the hyomandibular. On the other hand, the
proximal extremity of the quadrate cartilage atrophies, loses
its direct connection with the periotic capsule, and becomes
distinctly ossified, as the metapterygoid. In the Sharks, even
the ascending, metapterygoid, part of the quadrate, is lost.

The quadrate and supra-stapedial portions of the first and
second visceral arches coalesce in the Chimcera^ Dipnoi^ and
many AmpJiihia^ into a single cartilaginous plate.

In the JSIaintnalia^ and to some extent in Aves^ osseous
matter is deposited in the fibrous tissue wdiich surrounds the
sides and base of the tympanic membrane, and gives rise to a
special tymjxmiG bone. In most Mammalia^ ossification ex-
tends into the sides and floor of the tympanum and external
meatus ; and a process of integument, chiefly derived from the
second visceral arch, is converted into a concha^ or external ear.

The Organ of Taste is the mucous membrane which covers
the tongue, especially its posterior region, and probably also
a part of thatlining the fauces. When the sense is well de-
veloped, the mucous membrane is raised into numerous papillae
of various forms, and is well supplied with filaments from the
glossopharyngeal nerve.

The sense of Touch is difi'used over the integimient and
over the mucous membrane of the buccal cavity, which is,
strictly speaking, a part of the integument.

As special organs of touch in the higher Vertehrcita, the
nervous papilla?, containing " tactile corpuscles,'''' and the long
facial hairs, the papillae of which are well supplied with nerves,
termed vibrissce, may be mentioned.

In most, if not all Fishes, the integument of the body and
of the head contains a series of sacs, or canals, usually disposed
symmetrically on each side of the middle line, and filled with
a clear gelatinous substance, ^he w^alls of the sacs, or canals,
are abundantly supplied with nerves, and the terminations of
the latter enter rounded papillce, which project into the gelati-
nous contents. These sensory organs are known as the " or-

rnE LIYEH AND THE TEETH. 79

gans of the lateral Ime^"^ or " mucous canals ; " and they
were formerly supposed to be the secretory gUinds of the
slimy matter which coats the bodies of fishes, and which is
really modified epidermis.

The Alimentary Canal. — This part of vertebrate organi-
zation always exhibits a differentiation into mouth, pharynx,
oesophagus, stomach, and intestine ; and the last has always
a median, or nearly median, aperture on the ventral surface
of the body. It may open by itself ; or into a cloaca^ or cham-
ber common to it, the urinary and the genital organs.

The intestine is generally distinguishable into small and
large ; and, at the junction of the two, one or two ccfica are
frequently developed from the former.

Tlie stomach and intestine are invested by a peritoneal
membrane, and connected, by niesogastric and 7nesenteriG folds
of that membrane, with the median dorsal wall of the abdomi-
nal cavity. Glands appertaining to the lymphatic system
frequently abound in the mesenteric folds, and a highly-vas-
cular gland of this system, the spleen^ is always (except in
Amjy/iioxus, 3fi/xine, and the Leptoceplialidc^ developed in
close proximity to the stomach. A pancreatic gland very
generally pours its secretion into the anterior end of the intes-
tine. Salivary gkmds very commonly open into the mouth ;
and, in the higher Vertebrata, anal glands are not unusually
developed in connection with the termination of the rectum.

The structures connected with the alimentary canal of ver-
tebrate animals, which are most characteristic and peculiar,
are the liver and the teeth.

The Liver, — In invertebrate animals this organ is alwa3^s
ultimately resolvable into caecal tubes, the ends of the hepatic
ducts, which are lined with an epithelium, and not reticulated ;
and it has no receptacle for the bile. In most Vertehrata the
ends of the hepatic ducts have not been satisfactorily traced,
nor is it certain that the immense proportional mass of hepatic
corpuscles is contained in tubes continuous with them ; if such
be the case, the tubes must be reticulated. The ducts of the
vertebrate liver very frequently pour the bile, directly or in-
directly, into a receptacle, the gall-bladder. Am]jhioxus stands
alone among vertebrated animals, in having a ciscal diverticu-
lum of the intestine for a liver.

The Teeth. — Teeth, in llollusca and Annulosa^ are always

BO THE ANATOMY OF VERTEBRATED ANIMALS.

"ecderonic," cuticular, or epithelial structures. In Vertebrata
true teeth are invariably " enderonic," or developed, not from
the epithelium of the mucous membrane of the alimentary
canal, but from a layer between this and the vascular deep
substance of the enderon, which answers to the dermis in the
integument. The horny " teeth " of the Lampreys, and of
Ornithorhynchus^ appear to be ecderonic structures, homolo-
gous with the " haleen " of the Cetacea^ with the palatal
plates of the Sirenia, or the beaks of Birds and Reptiles, and
not with true teeth.

The dense calcified tissue called dentine, characterized bv
the close-set parallel tubuli which radiate through it, branch-
ing as they go, constitutes the chief mass of true teeth ; but
the dentine may be coated with ordinary bony tissue, which
then receives the name of cementum^ and its crown may be
capped with imperforate, prismatically fibrous, enamel.

The teeth are moulded upon papillas of the mucous mem-
brane, which may be exposed, but are more usually sunk in a
fold or pit, the roof of w^hich may close in so as to form a
dental sac. And there may be one set of teeth, or several ;
the sacs of the new teeth, in the latter case, being developed
either as diverticula of the old ones, or independently of them.

In the majority of the Mammalia the teeth are limited in
number, as well as definite in their forms and their mode of
succession. There are two sets of teeth, forming a first, decidu-
ous^ or m,ilk dentition^ and a second, or permanent dentition.
The deciduous dentition, when most comjiletely developed, con-
sists of incisor^ canine^ and molar teeth. The incisors are
distinguished from the rest by the lodgment of the upjoer set
in the premaxillce, and the correspondence of the lower set
with the upper. Their number and form vary. The distinc-
tion between canines and molars is one of form and position
in regard to the remaining teeth ; the most anterior of the
teeth behind the premaxillo-maxillary suture, if it is sharp and
projecting, receiving the name of canine. There are never
more than four canines. The other teeth are molars, and
ordinarily do not exceed four upon each side, above and below.
What is called a dental formida is a conv^enient combination
of letters and figures for making the number and disposition
of the teeth obvious. Thus, let di., c?c, dm^ represent, respec-
tively, the deciduous or milk set of incisors, canines, and
molars. Then, by placing after each of these symbols figures
arranged so as to show the number of the teeth of the kind
symbolized, on each side of each jaw, we shall have the dental

DENTAL FORMULiE. 81

foz-iniila of a gr/eu animal. The dental formula of a cliild

over two years of ao-c is thus — di. r^ dc. ^ — - dm. -^ = 20:

° 2.2 1—1 2.2

wliicli means that the cliild sliould have two incisors, one
canine, and two molars on each side of eacli jaw.

The neck of the sac of each deciduous tooth gives off a
diverticulum, in Avliich one of the permanent teeth is de-
veloped; as it grows, it causes the absorption of the 'fang
of the corresponding deciduous tooth, which thus becomes
shed, and is replaced from below by the permanent tooth.
The same letters, but without the prefix c7, are used for the
permanent incisors and canines ; but the permanent teeth,
which replace the deciduous molars, are called premolars^
and haA^e the symbol /^m. Furthermore, three or, it may be,
four permanent grinding teeth, on each side of each jaw, are
developed altogether behind the milk molars, and thus come
into place without replacing any other tooth from below.
These are called molars^ and have the syml)ol m. Thus the
<brmula of the permanent dentition in Man is written :

?.. ^— rC. - — ^i>^^. ^T^ ^^. 5-5 = ^'' ; there bemg two mcisors,

Z.A) 1 1 Z./i) 0.0

one canine, two premolars, and three molars on each side
above and below. It is a rule of very general application
among the 3Iamracdla^ that the most anterior molar comes
into place and use before the deciduous molars are shed.
Hence, when the hindermost premolar, which immediately
precedes the first molar, comes into use by the shedding of
the last milk molar, the crown of the first molar is already a
little ground down ; and this excess of w^ear of the first molar
over the adjacent premolar long remains obvious. The fact
that, in the permanent dentition, the last premolar is less
worn than the first molar which immediately follow'S it, is
often a valuable aid in distinguishing the premolar from the
molar series.

No vertebrate animal has teeth in any part of the alimen-
tary canal save the mouth and pharynx — except a snake
(Rachiodon) ^ which has a series of what must be termed
teeth, formed by the projection of the inferior spinous pro-
cesses of numerous anterior vertebrjB into the oesophagus.
And, in the highest 'Vertehrata^ teeth are confined to the pre-
maxillie, maxillae, and mandible.

Tlie Circidatory Organs. — The heart of the vertebrate
embryo is at first a simple tube, the anterior end of which

82 THE ANATOMY OF VERTEBRATED ANIMALS.

passes into a cardiac aortic trunk, wliile the posterior end i3
continuous with the great veins which bring back blood from
the umbilical vesicle — the omplialomeseraic veins.

The cardiac aorta immediately divides into two branches,
each of which ascends, in the first visceral arch, in the form
of a forwardly convex aortic arch^ to the under side of the
rudimentary spinal column, and then runs, parallel with it a
fello'W, to the hinder part of the body, as a prbniti-ce subverted
bral aorta. The two primitive aortas very soon coalesce
throughout the greater part of their length into one trunk,
the defiiiitive subvertebral aorta ; but the aortic arches, sepa-
rated by the alimentary tract, remain distinct. Additional
arterial trunks, to the number of four in the higher Verte-
hrata^ and more in the lower, are successively developed,
behind the first, in the other visceral arches, and further con-
nect the cardiac and subvertebral aortse.

In the permanently branchiate Vertebrata^ the majority of
these aortic arches persist, giving off vessels to the branchial
tufts, and becoming converted into afferent and efferent
trunks, which carry the blood to and take it from these tufts.
(Fig. 25, A, B, C, D, E.)^

In the higher Jimphibia, which, though branchiate in the
young state, become entirely air-breathers in the adult con-
dition, such as the JBatrachia (Fig. 25, F) and Ccecilia, the
permeable aortic arches are reduced to two (the middle pair
of the three which supply the external gills, and the fourth
pair of embryonic aortic arches) by the obliteration of the
cavities of the dorsal ends of the others. Of the posterior
arches, the remains of the fifth and sixth become the trunks
which give off the pulmonary arteries, and, in the JBatrachia,
cutaneous branches. The anterior, or third, primitive aortic
arch becomes the common carotid trunk, and ends in the
carotid gland^ whence the internal and external carotids
arise. In those Vertebrata which never possess gills, the
arches become reduced either to two pair, as in some Lacer-
tilia / or to one pair, as in other Jiej^tilia / or to a single
arch, as in A.ves and 3IaimnaUa. The aortic arches tlms
retained are, in the Lizards in question, the third and the
fourth pairs iu order from before backward ; but the fourth
pair only, in other Reptiles ; in Birds, the right arch only of
the fourth pair ; and in Mammals, the left arch only of the
fourth pair. The fifth pair of arches giv^e off the pulmonary
arteries, the so-called " ductus arteriosus " representing the
remains of the primitive connection of these arches with the

MODIFICATIONS OF THE AORTIC ARCHES.

83

fourth pair and the subvcrtebral aorta. The dorsal ends of
the first, second, and third arches become obliterated ; but
their cardiac ends, and the branches which they give off, be-
come the arteries of the head and upper extremities.

Mn. JTy. BrJ J3r.^ Bn^ Bn^Br^ Br:° Bi:''

I I ' 1 L i I I

TAT).

-AC

n m IV" V VI \ui viu K

Fig. 25. — A diagram intended to show the manner in which the aortic arches become modi-
fied in the series of the Verteh?xtta.

k. A hj-pothetically perfect series of aortic arches, correspondinf^ with the nine postoral vis-
ceral arches, of which evidence is to be found in some Sharks and M/rrslpobrmichii.
AG. Cardiac aorta; AB. Dorsal or sub vertebral aorta, i-ix the aortic arches corre-
sponding with 3/«., the mandibular; Hy., the hyoidean, and Br. ' — Br.'., the seven
branchial viscci-al ai-ches. i, ii, in, iv, v, vi, vii, the seven branchi<il clefts. The lirst

84 THE ANATOMY OF VERTEBRATED ANIMALS.

msceral cleft is left unnumbered, and one must be added to the number of each bran-
chial cleft to give its number in the series of visceral clefts.

B. Hypothetical diagram of the aortic arches in the Shark HeptancJiUS, which has seven

branchial clefts. Sj). The remains of the first \'isceral cleft as the sphacle. Branchise
are developed on all the arches.

C. Lepido&iren. — The first arch has disappeared as such, and the first visceral cleft is ob-

literated. Internal branchiae are developed in connection -with the second, filth, sixth,
and seventh aortic arches; external branchias in connection with the fourth, fifth, and
sixth. PA. — The pulmonary artery. The posterior two visceral clefts are obliterated.

D. A Teleosteau Fish. — The first aortic arch and fu-st visceral cleft are obhterated as before.

The second aortic arch bears the pseudo-branchia (Ps.-S.), whence issues the ophthalmic
artery, to terminate in the choroid gland {Ch.). The next four arches bear giUs. The
seventh and eighth arches have been observed in the embryo, but not the ninth, and
the included clefts are absent in the adult,

E. The Axolotl {Siredon), a perennibranchiate amphibian. The third, fourth, fifth, and

sLxth aortic arches, and the anterior four branchial clefts, persist. The first visceral
cleft is obliterated.
E The Frog. — The three anterior aortic arches are obhterated in the adult. The place of
the third, which is connected with the anterior external gill in the Tadpole, is occupied
by the common carotid and the rete mirabile (carotid gland, Ca. G.) which terminates
it. The fourth pair of aortic arches persist. The fifth and sixth pair lose their connec-
'tions with the subvertebral aortic trunk, and become the roots of the cutaneous and
pulmonary arteries. The first visceral cleft becomes the tympanum, but all the others
are obhterated in the adult.

The embryonic aorta gives off omphcdomeseraic branches
(Fig. 26, 6) to the umbilical vesicle ; and ends, at first, in the
hypogastric arteries (which are distributed to the allantois in
the abranchiate Vertehrata)., and a median caudal continuation.
The blood from the umbilical vesicle is brought back, as before
mentioned, by the omphalomeseraic veins (Fig. 26, o'), which
unite in a dilatation close to the head ; the dilatation (smus
ve?iosus) receives, on each side, a short transverse venous
trunk, the ductus Cuvieri (Fig. 26, DC)., w^hich is itself
formed, upon each side, by the junction of the anterior and
posterior cardinal veins, which run backward and forward,
parallel with the spine, and bring back the blood of the head
and of the trunk.

The blood of the allantois is returned by the umbilical
vein., or veins (Fig. 26, i«'), which are formed in the anterior
wall of the abdomen, and open into the venous sinus before
mentioned. The blood of the posterior extremities and kid-
neys is, after a while, brought to the same point by a special
median vein, the veiia cava inferior (Fig. 26, cv).

The development of the liver effects the first great change
in the arrangements now described. It, as it were, interrupts
the course of the omphalomeseraic vein, w^hich is not only the
vein of the umbilical sac but also that of the intestine, and
converts it into a mesh work of canals, which communicate, on
one side, w4th the cardiac part of the vein, and, on the other
Bide, with its intestinal part. The latter is thus converted into
the ve7ia portce (Fig. 26, vp)., distributing the blood of the
stomach and intestines to the liver ; w^hile the former becomes

THE DEVELOPMENT OF THE VASCULAR SYSTEM. 85

the JiepatiG vein (yA), carrying the hepatic blood to the in-
ferior cava, and thence to the heart.

The umbilical vein further gives a branch to the liver ;
while, on the other hand, it communicates directly with the
venous sinus (now almost merged in the vena cava inferior)
by a trunk called ductus venosus (Fig. 26, Du).

Fic 26.— Diaqrram of the arrangement of the principal vessels in a human foetus. — IT, th<
heart ; TA, the aortic trunk or cardiac aorta ; c, the common carotid ; c', the external
carotid ; g'\ the internal carotid ; s, subclavian ; v, vertebral artery ; 1, 2, 3, 4, 5, th8
aortic arches — the persistent Ze/Y aortic arch is hidden. A\ subvertebral aorta; o, om-
phalomeseraic artery, going to the umbihcal vesicle -y, with its vitelliae duct dv ; o, om-
phalomeseraic vein ; V2}, the vena portas ; L, the liver ; im, the hypogastric or umbilical
arteries, with their placental ramifications, m" v/' ; w', the umbihcal vein ; Z>», the ductus
venosus; -^/i. tiie hepatic vein ; cy, the vena cava inferior ; t'iZ. the ihac veins ; as, a vena
azj^gos ; vc', a vena cardinalis posterior; Z>(7, a ductus Citvieri; the anterior cardinal
vein is seen commencing in the head and running down to the ductus Cuvieri on the
under side of the numbers 1, 2, 3, 4, 5 ; P, the lungs.

When the umbilical vesicle and allantois cease to have any
further import, as at birth, or before, the omphalomeseraic ar-
teries have become intestinal arteries, and the omphalomeseraic
vein, the vena portoe. The hypogastric arteries are obliter-
ated, except so much of them as is converted into the common
iliac arteries. The umbilical vein, or veins, also disappear, or
are represented by mere ligaments.

B6 THE ANATOMY OF YERTEBIIATED ANIMALS.

Of tlie three veins wliicli open into the venous sac — viz.,
the inferior cava, and the right and left ductus Cuvieri — all
may persist, the latter receiving the title of right and left sur
perior cavce. Or, as very often happens in the higher Verte-
hrata^ the left ductus Cuvieri becomes more or less obliterated ;
the veins which properly open into it acquiring a connection
v^'ith the right ductus^ which then remains as the sole superior
cava. The posterior cardinal veins give off anastomosing
branches, which are converted into the veiice azygos j the an-
terior cardinal veins become metamorphosed into the external
jugular veins and venae innominatce.

In Fishes, the sinus venosus and the cardinal veins persist
throuo'hout life ; but the anterior cardinal veins, which brins*
back the blood from the head and from the anterior extremi-
ties, are called ve7ia3 jugulares.

The caudal veins are either directly continued into the
cardinal veins, as in Marsipohrancliii and Elasmohranchii, or
branch out into the kidneys, as in many Teleostei, In either
case the efferent renal veins open into the cardinal veins.

The portal veins, conveying the blood of the chylopoietic
viscera, and sometimes that of other organs and of the abdomi-
nal walls, may be one or many. In A.mp)hioxus and 3Iyxine
the vein is rhythmically contractile, and forms a portal heart.

In most Amphibia and Heptilia the sinus venosus persists,
and is rhythmically contractile, valves being placed at its
opening into the right auricle.

The anterior cardinal veins are represented by jugular
veins, the posterior cardinal by vertebral veins ; these, and the
veins of the anterior extremities, when they are present, pour
their blood into the ductus Cuvieri, which are now termed an-
terior vencB cavce.

The veJia cava inferior takes its origin chiefly by the coa-
lescence of the efferent veins of the kidneys and reproductive
organs, and does not always receive the whole of the hepatic
veins — more or fewer of the latter opening independently into
the sinus venosus.

The blood which leaves the kidneys b}- its efferent veins
is supplied, not only by the renal arteries, but by the veins of
the caudal region, and of the hinder extremities, which branch
out like a vena portce in the substance of the kidneys. This
renal portal system is less developed in Heptilia than in Am.-
p>hihia. All the blood of the posterior extremities and caudal
region does not traverse the kidneys, however, more or less
of it being led away by great branches of the iliac veins, which

THE MODIFICATIONS OF THE VASCULAR SYSTEM. 87

run along the anterior wall of tlie abdominal cavity, either as
two trunks, or united into one. These vence ahdominales an-
teriores are eventually distributed to the liver, along with the
branches of the proper veriw portm.

In £irds, the sinus venosus is not distinct from tlie rio'ht
auricle, and there are tv/o anterior venm cavm. The vena
cava inferior arises, as in Mammals, by the union of the two
common iliac veins. It receives both the right and the left
hepatic veins, and, in addition, the anterior abdominal vein no
longer enters the portal system, but passes up the anterior
wall of the abdomen and through the hepatic fissure to join
the inferior cava.

The caudal and pelvic veins unite into three principal
trunks, of which one is median and tv/o are lateral. The
median enters into the portal system. The lateral branches
pass along and through the kidney, receiving veins from it,
but giving none to it ; and eventually, after receiving the
ischiatic veins, unite with the crural veins to form the common
iliacs. Thus there is no renal portal system in birds.

In Mammalia^ the sinus venosus is not distinct from the
right auricle. The anterior cavm are frequently reduced to
one, the right. The ve7\a cava inferior commences in the
caudal region, and receives all the blood of the posterior
moiety of the body, except so much as is carried away by the
azygous veins. The anterior abdominal veins are represented
only during foetal life, by the umbilical vein or veins. The
efferent veins of the kidneys open directly into the trunk of
the inferior vena cava, and the portal vein is comjDosed
exclusively of radicles proceeding from the chylopoietic
viscera.

Many of the veins of AmpTiioxus^ the portal vein of MyX'
ine^ dilatations of the caudal vein in the Eel, the vena3 cavas
and the iliac and axillary veins of many Anipliihia^ the veins
of the wing of Bats, possess a rhythmical contractility, which,
in combination with the disposition of their valves, assists the
circulation of the blood.

In Vertehrata of all classes, and in very diverse parts of
the body, both veins and arteries occasionally break up into
numerous branches of nearly equal size, which may or may
not unite again into larger trunks. These are called retia
mirabiUa,

Modifications of the Heart. — Great changes go on m the
structure of the heart, j(9ar^Je>a5Sw with the modifications of the

88 THE ANATOMY OF VEKTEBRATED ANIMALS.

rest of the circulatory system, in the development of the
highest Vertebrata. The primitively simple tube becomes
bent upon itself, and divided from before backward into an
aortic, or ventricular, and a venous, or auricular, portion. A
median septum then grows inward, dividing the auricular and
ventricular chambers into tw^o, so that a right auricle and
right ventricle become separated from a left auricle and left
ventricle. A similar longitudinal division is eifected in the
cardiac aorta. The septa are so disposed in the auriculo-ven-
tricular chamber that the right auricle communicates with the
venous sac and the trunks of the visceral and body veins,
while only the veins from the lungs enter into the left auricle.
And the cardiac aorta is so divided that the left ventricle com-
municates with the chief aortic trunk, the right with the pul-
monary artery. Valves are developed at the auriculo-ventric-
ular apertures and at the origins of the aortic and pulmonary
trunks, and thus the course of tlie circulation is determined.
The septum between the auricles remains incomplete for a
much longer period than that between the ventricles — and
the aperture by v/hich the auricles communicate is called the
foramen ovale.

In the adult state of A.ves and 3Iaminalia, the foramen
ovale is closed ; there is no direct communication between the
arterial and venous cavities or trunks ; there is only one aortic
arch ; and the pulmonary artery alone arises from the right
ventricle. In the Grocodilia, the auricles and ventricles of
opposite sides are completely separate ; but there are two
aortic arches, and one of these, the left, arises from the right
ventricle along with the pulmonary artery. In all Heptilia,
except Crocodiles, there is but one ventricular cavity, though
it may be divided more or less distinctly into a cavum veno-
sum and a cavum arteriosum. The auricles are completely
separated (except in some Ghelonia), and the blood of the
left auricle Hows directly into the cavum arteriosum, while
that of the right passes immediately into the cavum venosum.
The aortic arches and the pulmonary artery all arise from the
cavum venosum (or a special subdivision of that cavity called
the cavwn 2yul?nonale) ', the ostium of the pulmonary artery
being farthest from, and that of the right aortic arch nearest
to, the cavum arteriosum.

In all A.inphihia, the spongy interior of the ventricle is
andivided, and the heart is trilocular, though the auricular
septum is sometimes small and incomplete. In all Pisces, ex-
cept L'lpldosiren, there is no auricular septum. In Amphi'

THE MODIFICATIONS OF THE HEART. 89

ouus the heart 'remains in its primitive state of a simple, con-
tractile, undivided tube.

In the Ganoidei, the JSlasmohranchii^ and the Amphibia^
the walls of the enlarged commencement of the cardiac aorta,
called the hulbiis aortce^ contain striped muscular fibre, and
are rhythmically contractile.

The Ganoidei and Elasmohranchii possess, not merely the
ordinary semilunar valves, at the junction between the ventri-
cle and the cardiac aorta, but a variable number of additional
valves, set, in transverse rows, upon the inner wall of the
aortic bulb.

The change of position which the heart and the great ves-
sels of the highest Vertebixita undergo during embryonic life
is exceedingly remarkable, and is repeated as we ascend in the
series of adult vertebrates.

At first, the heart of a mammal lies under the middle of
the head, immediately behind the first visceral arches, in which
the first pair of aortic arches ascends. As the other pairs of
aortic arches are developed the heart moves backward ; but
the fourth pair of aortic arches, by the modification of one of
which the persistent aorta is formed, lies, at first, no farther
back than the occipital region of the skull, to Avhich, as we
have seen above, the fourth pair of visceral arches belongs.
As the two pairs of cornua of the hyoid belong to the second
and the third visceral arches, the larynx is probably developed
within the region of the fourth and fifth visceral arches ; hence,
the branches of the pneumogastric, with which it is supplied,
must, originally, pass directly to their destination. But, as
development proceeds, the aortic arches and the heart become
altogether detached from the visceral arches and move back,
until, at length, they are lodged deep in the thorax. Hence
the elongation of the carotid arteries ; hence also, as the
larynx remains relatively stationary, the singular course, in
the adult, of that branch of the pneumogastric, the recurrent
laryngecd^ w4iich primitively passed to the laryngeal region
behind the fourth aortic arch, and consequently becomes
drawn out into a long loop — the middle of it being, as it
were, pulled back, by the retrogression of the aortic arch into
tlie thorax.

The J^lood- Corpuscles. — Corj^uscles are contained in the
blood of all Vertebrata. In A^rqjhioxus they are all of one
kind, colorless and nucleated. The genus Leptoceplialus^
among the Teleostei, is said to possess the same peculiaritj'^ ;

90 THE ANATOMY OF VERTEBRATED ANIMALS.

but, in all other known Vertebrata, the blood contains corpus
cles of two kinds.

In Ichthyopsida and Sauropsida^ both kinds are nucleated ;
but one set are colorless, and exhibit amasboid movements,
while the others are red, and do not display contractility.
Except in the Marsipohranchii^ which have round blood-cor-
puscles, the red corpuscles are oval. They attain a larger size in
the perennibranchiate Ampliibia than in any other Vertebrates,

In Maminalia^ the blood-corpuscles are also of two kinds,
colorless and red, the colorless possessing, and the red being
devoid of, nuclei. It is but very rarely that a nucleated cor-
puscle, with a red color especially developed about the nu-
cleus, is seen in Mammalian blood ; but such cases do occur ;
and, from this and other circumstances, it is probable that the
Mammalian red corpuscle is a free-colored nucleus.

The colorless corpuscles of Maiiirrialia are spheroidal, and
exhibit amaeboid movements ; the red corpuscles are flattened,
usually circular, but sometimes oval ( Camelidw) disks, devoid
of contractility.

TJie Lymp)hatic System. — This system of vessels consists,
chiefly, of one or two princijDal trunks, the thoracic duct, or
ducts, which underlie the vertebral column, and communicate,
anteriorly, w^ith the superior vence cavse, or with the veins
which open into them.

From these trunks, branches are given oif, which ramify
through all parts of the body, except the bulb of the eye, the
cartilages, and the bones. In the higher Vertehrata, the
larger branches are like small veins, provided with definite
coats, and with valves opening toward the larger trunks, while
their terminal ramifications form a capillary net-work ; but, in
the lower Vertebrates, the lymphatic channels assume the form
of large and irregular sinuses, which not unfrequently com-
pletely surround the great vessels of the blood-s^^stem.

The lymphatics open into other parts of the venous S3's-
tem besides the affluents of the superior cavse. In Fishes
there are, usually, two caudal lymphatic sinuses wliich open
into the commencement of the caudal vein. In the Frog, foui
such sinuses communicate wuth the veins, two in the coccy*
goal, and two in the scapular, region. The walls of these si
nuses are muscular, and contract rhythmically, so that they re-
ceive the name of Lyinphatic hearts. The posterior pair of
these hearts, or non-pulsating sinuses corresponding with
them, are met with in Heptilla and Aves,

THE RESPIRATORI ORGANS. 91

Accumulations of indifferent tissue in tlie vralls of some of
the lymphatic sinuses are to be met Avith in Fishes ; but it is
only in the Grocodilia^ among Heptilla^ tliat an accumulation
of such tissue, traversed by lymphatic canals and blood-vessels,
is apparent, as a LympJiatio gland^ in the mesentery. Birds
possess a few glands in the cervical region ; and, in Mam-
raalia^ tliey are found, not only in the mesentery, but in many
parts of the body.

The Spleen is substantially a lymphatic gland. The Tliy-
mus — a glandular mass with an internal cavity, but devoid of
any duct — which is found in all Vertehrata except Amj^hioxus,
appears to belong to the same category. It is developed in
the neighborhood of the primitive aortic arches, and is double
in most of the loAver Vertebrata, but single in JIammalia.

The nature of two other " ductless glands," the Thyroid
gland and the Suprarenal capsules^ which occur very widely
among the Vertebrata, is by no means Avell understood.

The thyroid gland is a single or multiple organ, formed of
closed follicles, and is situated near the root of the aorta, or
the great lingual, or cervical, vessels which issue from it.

The suprarenal capsules are follicular organs, often abun-
dantly supplied with nerves, which appear to occur in Fishes,
and are very constant in the higher Vertebrata, at the anterior
ends of the true kidneys.

The Ijympli Corpuscles^ which float in the plasma of the
lymphatic fluid, always resemble the colorless corpuscles of
the blood.

The Respiratory Organs. — ^Vertebrated animals may pos
sess either branchicB for breathing the air contained in water,
or lungs for atmospheric respiration; or they may possess
both kinds of respiratory organs in combination.

Except in Amphioxus^ the branchice are always lamellar,
or filamentous, appendages of more or fewer of the visceral
arches ; being sometimes developed only on the proper bran-
chial arches, sometimes extending to the hyoidean arch, or
(as would appear to be the case with the spiracular bran-
chiae of some fishes) even to the mandibular arch. The bran-
chiae are always supplied with blood by the divisions of the
cardiac aorta ; and the difibrent trunks which carry the aerated
blood away, unite to form the subvertebral aorta, so that all
vertebrated animals Avith exclusively branchial respiration
have the heart filled Avith venous blood.

In the early life of many branchiated Vertebrata^ the bran-

P2 THE ANATOMY OF VERTEBRATED ANIMALS.

chisB project freely from the visceral arches to which they are
attached, on the exterior of the body ; and in some Am2yhihia^
such as the Axolotl [jSiredo?i), they retain their form of exter-
nal plume-like appendages of the neck throughout life. But
in the adult life of most Fishes, and in the more advanced con-
dition of the Tadpoles of the higher AmpJdhia^ the branchiae are
internal^ being composed of shorter processes, or ridges, which
do not project beyond the outer edges of the branchial clefts;
and, generally, become covered by an operculum developed
from the second visceral arch.

The lungs of vertebrated animals are sacs, capable of being
filled with air, and developed from the ventral wall of the
pharynx, wdth w^iich they remain connected by a shorter or
longer tube, the trachea^ the division of this for each luug
being a bronchus. Venous blood is conveyed to them directly
from the heart by the pulmonary arteries, and some * or all
of the blood which they receive goes back, no less directly, to
the same organ by the pulmonary veins.

The vascular distribution thus described constitutes an es-
sential part of the definition of a lung, as many fishes possess
hollow sacs filled with air ; and these sacs are developed, oc-
casionally, from the ventral, though more commonly from the
dorsal, wall of the pharj'-nx, oesophagus, or stomach. But
such air-sacs — even when they remain permanently connected
with the exterior by an open passage or i^neiunatiG duct — are
air-bladders^ and not lungs, because they receive their blood
from the adjacent arteries of the body, and not direct from the
heart, while their efferent vessels are connected only with the
veins of the general circulation.

The wall of each pulmonic air-sac is at first quite simple,
but it soon becomes cellular by the sacculation of its parietes.
In the lower pulmonated Vertebrata, the sacculation is more
marked near the entrance of the bronchus ; and when the lung-
sac is long, as in many Amphibia and in Snakes, the walls of
the posterior end may retain the smooth condition of the em-
bryonic lung. In Chelonia and Crocodllla, the lung is com-
pletely cellular throughout, but the bronchi do not give off
branches in the lungs. In Birds, branches are given off at
right angles ; and, from these, secondary branches, w^hich lie
parallel with one another, and eventually anastomose. In
Mammalia., the bronchi divide dichotomously into finer and
finer bronchial tubes, which end in sacculated air-cells.

* Generally all, but in some AnipMMa, such as Proteus^ part of tlie blood
supplied to the lungs enters the general circulation.

THE ORGANS OF VOICE. 93

Blind air-sacs are given off from the surfaces of the lungs
in the Ghammleonidm^ and the principal bronchial tubes termi-
nate in large air-sacs in Aves.

The Larynx and the Syrinx. — The trachea is commonly
kept open by complete, or incomplete, rings of cartilage, and
the uppermost of these undergo special modifications, which
convert them into a Larynx^ an organ which, under certain
circumstances, becomes an instrument of voice.

When completely developed, the larynx presents a ring-
like cartilasre called cricoid^ which lies at the summit of the
trachea. With the anterior and dorsal edge of this, two aryt-
enoid cartilages are movably articulated, and a thyroid car-
tilage of a V-shape, open behind, is articulated movably with
its sides. Folds of the mucous membrane, containing elastic
tissue, termed the vocal cords^ stretch from the arytenoid car-
tilages to the reentering angle of the thyroid cartilage, and
between them lies a slit-like passage, the glottis. This is cov-
ered by a cartilage, the epiglottis^ attached to the reentering
angle of the thyroid, and to the base of the tongue. Folds
of mucous membrane, extending from the epiglottis to the
arytenoid cartilages, are the aryepiglottic hgaments. The in-
ner surfaces of these end below in the false vocal cords, he-
tween which and the true chordcB vocales lie recesses of the
mucous membrane, the ventricles of the larynx.

The chief accessory cartilages are the cartilages of JSan-
torini, attached to the summits of the arytenoid cartilages,
and the cartilages of Wrisberg^ which lie within the aryep^-
glottic ligaments.

Birds possess a larynx in the ordinary position ; but it is
another apparatus, the loicer larynx or syrinx, developed
either at the end of the trachea, or at the commencement of
each bronchus, which is their great vocal organ.

The Mechanism of JRespiration. — The mechanism by which
the aerating medium is renewed in these different respiratory
organs is very various. Among branchiated Vertebrata, Am-
phioxus stands alone in having ciliated branchial organs, which
form a net-work very similar to the perforated pharyngeal a "all
of the Asciclians. Most Fishes breathe by taking aerated wa-
ter in at the mouth, and then shutting the oral aperture, and
forcing the water through the branchial clefts, Avhen it flows
over the branchial filaments.

Pulmonated Vertebrata, which have the thoracic skeleton
Incomplete (as the Amphibia), breathe by distending their
pharyngeal cavity with air; and then, the mouth and nostrils

94 THE ANATOMY OF VERTEBRATED ANIMALS.

being sliut, pumping it, by the elevation of the liyoidean ap-
paratus and floor of the pharjmx, into the lungs. A Frog, there-
fore, cannot breathe properly if its mouth is kept wide open.

In most JRepiilla^ and in all Aves and Maininalla^ the ster-
num and ribs are capable of moving in such a way as alter-
nately to increase and diminish the capacity of the thoracico-
abdominal cavity, and thereby to give rise to an inspiratory
and expiratory flow of air.

In the Heptllla, the elastic lungs dilate with the inspira-
tory, and contract with the expiratory, act ; but, in Aves, the
air rushes through the principal bronchial passages of the fixed
and little distensible luno-s, into the verv dilatable and com-
pressible air-sacs. From these the act of expiration expels it
back through the principal bronchial passages to the trachea,
and so out of the body.

Both in Heptllia (e. g., Chelonia) and in Aves, muscular
fibres pass from the ribs to the surface of the lungs beneath
the pleuroperitoneal membrane, and this rudimentary dia-
phragm acquires a very considerable development in the Ha-
tltce, or strutliious birds. So far as the contraction of these
fibres tends to remove the ventral from the dorsal walls of the
lungs, they must assist inspiration. But this diaphragmatic in-
spiration remains far weaker than the sterno-costal inspiration.

Finally, in the 3Iaininalia, there are two equally-important
respiratory pumps, the one sterno-costal, the other diaphrag-
matic. The diaphragm, though it makes its appearance in
Sauropsida, only becomes a complete partition between the
thorax and the abdomen in mammals ; and, as its form is such
that, in a state of rest, it is concave toward the abdominal
cavity, and convex toward the thorax, the result of its con-
traction, and consequent flattening, necessarily is to increase
the capacity of the thorax, and thus pump the air into the
elastic lungs, which occupy a large part of the thoracic cavity.
When the diaphragm ceases to contract, the elasticity of the
lungs is sufficient to expel the air taken in.

Thus, mammals have two kinds of respiratory mechanism,
either of which is efficient by itself, and may be carried on in-
dependently of the other.

The Renal Orgayis. — The higher Vertehrata are all pro-
vided with two sets of renal organs, the one existing only dur-
ing the early foetal state, the other persisting throughout life.

The former are the Wolffian bodies, the latter the true
Kidneys.

fUE REPRODUCTIVE ORGANS. 95

The Wolffian bodies make their appearance very early, on
each side of the ventral aspect of the si3inal region of the em-
bryOy as small transversely-disposed tubuli, opening into a duct
which lies upon their outer side, and enters, posteriorly, into
the base of the allantois, and thence into the primitive cloaca
with which that structure is connected. The Wolffian duct is
one of the first-formed structures in the embryo, and precedes
the tubuli.

The Kidneys appear behind the Wolffian bodies, and, ap-
parently, independently of them ; their ducts, the ureters^ are
also distinct, but likewise terminate in the pelvic part of the
allantois. Thus the urinary secretion passes into the allantois,
and it is that portion of this organ which lies within the abdo-
men, and becomes shut oif from the rest by the constriction
and obliteration of the cavity of an intermediate part, and its
conversion into the uraclms^ that gives rise to the urmary
bladder. The ultimate secreting tubuh of both the Wolffian
body and the kidney, are alike remarkable for ending in dila-
tations which embrace convoluted capillaries — the so-called
Malpightan tufts. Neither Wolffian bodies nor kidneys have
been observed in Amphioxus. It is doubtful whether true
kidneys are developed in Iclithyopsida^ or whether the so-
called kidneys of these animals are not, rather, persistent Wolf-
fian bodies.

The Reproductive Organs. — These, in vertebrated animals,
are primitively similar in both sexes, and arise on the inner
side of the Wolffian bodies, and in front of the kidneys, in the
abdominal cavity. In the female the organ becomes an ovari-
um. This, in some few fishes, sheds its ova, as soon as they
are ripened, into the peritoneal cavity, whence they escape by
abdominal pores, wliich place that cavity in direct communi-
cation wdth the exterior. In many fishes, the bvaries become
tubular glands, provided with continuous ducts, which open
externally, above and behind the anus. But, in all other Ver-
tehrata, the ovaries are glands without continuous ducts, and
which discharge their ova from sacs, the Graafian follicles,
successively developed in their solid substance. Nevertheless,
these ova do not fall into the peritoneal cavity, but are con-
veyed away by a special apparatus, consisting of the Fallopian
tubes, which result from the modification of certain embryonic
structures called the MiXllerian ducts.

The Miillerian ducts are canals which make their appear-
ance alongside the ducts of the Wolffian bodies, but, through-

96 THE ANATOMY OF VERTEBRATED ANIMALS.

out their whole extent, remain distinct from them. Their
proximal ends lie close to the ovary, and become open and
dilated to form the so-called ostia. I3ejond these ostia they
generally remain narrow for a space, but, toward their hinder
openings into the genito-urinary part of the cloaca, they com-
monly dilate again. In all animals but the didelphous and
monodelphous Mammalia^ the Mullerian ducts undergo no
further modification of any great morphological importance ;
but, in the monodelphous 3Iaininalia^ they become united, at
a short distance in front of their posterior ends ; and then the
segments between the latter and the point of union, or still
farther forward, coalesce into one. By this process of conflu-
ence the Mullerian ducts are primarily converted into a single
vagina with two uteri opening into it ; but, in most of the
Monodelphia^ the two uteri also more or less completely coa-
lesce, until both Mullerian ducts are represented by a single
vagina, a single uterus, and two Fallopian tubes. The didel-
phous Mammalia have two vaginae which m.ay, or may not,
coalesce anteriorly for a short extent ; but the two uteri re-
main perfectly distinct. So that what takes place in them is,
probably, a differentiation of each Mullerian duct into Fallo-
pian tube, uterus, and vagina, with or without the union of
the two latter, to the extent to which it is effected in the ear-
lier stages of development in Monodelphia. The Wolffian
ducts of the female either persist as canals, the so-called ca-
nals of Gaertner, which open into the vagina, or disappear
altogether. Remains of the Wolffian bodies constitute the
parovaria^ observable in certain female mammals.

In the male vertebrate embryo, the testis^ or essential re-
productive organ, occupies the same position, in front of the
Wolffian body, as the ovary ; and, like the latter, is composed
of indifferent tissue. In Aimpjhioxus and in the 3farsip)o-
branchii^ this tissue appears to pass directly into spermatozoa ;
but, in most Vertehrata^ it acquires a saccular or tubular struct-
ure, and from the epithelium of the sacs, or tubuli, the sperma-
tozoa are developed. At first, the testis is as completely de-
void of any excretory canal as the ovary ; but, in the higher
vertebrates, this want is speedily supplied by the Wolffian
bodv, certain of the tubuli of which becom.e continuous with
the tubuli seminiferi^ and constitute the vasa recta^ while the
rest abort. The Wolffian duct thus becomes the vas deferens^
or excretory duct of the testis ; and its anterior end, coiling on
itself, gives rise to the epididymis, A vesicula seininalis is a

THE REPRODUCTIVE ORGANS.

97

diverticulum of tlie vas deferens, near its posterior end, which
serves as a receptacle for the semen.

Wd M

Fia. 27. — Diagram exhibiting the relations of the female (the left-hand figure, $ ) and of tha
male (the right-hand figure, $ ) reproductive organs to the general plan (the middle fig-
ui*e) of these organs in the higher Vertebrada.

CI, the cloaca ; iJ, the rectum ; Bl, the urinary bladder ; IT, the ureter ; K, the kid-
ney; Uh, the urethra; (r, the genital gland, ovary, or testis; TF, the "Wolffian body;
W(l, the Wolffian duct; M, the Miillerian duct; Pst, prostate gland; Qj, Cowper''8
gland ; Csp, the corpus spongiosum ; Cc, the corpus cavernosum.

In the female, F, the vagina ; Ut, uterus ; Fp, the Fallopian tube ; Gt, Gaertner's
duct; P.», the parovarium; A, the anus; (7c, Csp, the clitoris. In the male, Csp, (7c,
the penis ; Ut, the uterus masculinus ; F«, vesicula seminalis ; Fc?, the vas deferens.

If the Wolffian bodies, the genitalia, and the alimentary
canal of a vertebrate embryo, communicated with the exterior
by apertures having the same relative position as the organs
themselves, the anus would be in front and lowest, the Wolf-
Qan apertures behind and highest, and the genital apertures
would lie between the two. But the anal, genital, and uri-
nary apertures are found thus related only among certain
groups of fishes, such as the Teleostei. In all other Vertehrata
there is either a cloaca^ or common chamber, into which the
rectum, genital, and urinary organs open ; or, the anus is a

98 THE ANATOMY OF VERTEBRATED ANIMALS

distinct posterior and superior aperture, and the opening of a
genito-urinary sinus, common to the urinary and reproductive
organs, lies in front of it, separated by a more or less consid-
erable permmum.

These conditions of adult Vertehrata repeat the states
through which the embryo of the highest vertebrates pass.
At a very early stage, an involution of the external integu-
ment gives rise to a cloaca, which receives the allantois, the
ureters, the Wolffian and Mullerian ducts, in front, and the
rectum behind. But, as development advances, the rectal di-
vision of the cloaca becomes shut off from the other, and opens
by a separate aperture — the definitive mms, which thus ap-
pears to be distinct, morphologically, from the anus of an osse
ous fish. For a time, the anterior, or genito-urinary part of
the cloaca, is, to a certain extent, distinct from the rectal di-
vision, though the two have a common termination ; and this
condition is repeated in jives, and in ornithodelphous Mam/-
malia, where the bladder, the genital ducts, and the ureters, all
open separately from the rectum into a genito-urinary sinus.

In the male sex, as development advances, this genito-
urinary sinus becomes elongated, muscular, and surrounded,
w4iere the bladder passes into it, by a peculiar gland, the jf^ros-
tate. It thus becomes converted into what are termed the
fundus, and neck of the bladder, with the prostatic and mem-
hranous portions of the urethra. Concomitantly with these
changes, a process of the ventral wall of the cloaca makes its
ajopearance, and is the rudiment of the intromittent organ, or
penis. Peculiar erectile vascular tissue, developed within
this body, gives rise to the median corp)US spongiosum and
the lateral corpora cavernosa. The penis gradualty protrudes
from the cloaca ; and, while the corpus spongiosum terminates
the anterior end of it, as the glands, the corpora cavernosa at-
tach themselves, posteriorly, to the iscliia. The under, or pos-
terior, surface of the penis is, at first, simply grooved ; by de-
grees the two sides of the groove unite, and form a complete
tube embraced by the corpus spongiosum. The penial urethra
is the result.

Into the posterior part of this penial urethra, which is
f^riqucntly dilated into the so-called hidbiis urethrm, glands,
called CoiC2Jer''s glands, commonly pour their secretion ; and
the penial, membranous, and prostatic portions of the urethra
(genito-urinary sinus) uniting into one tube, the male defmtive
urethra is finally formed.

In sundry birds and reptiles, the penis remains in the con*

MODIFICATIONS OF THE REFRODUCTIVE ORGANS. 99

dition of a process of tlie ventral wall of the cloaca, grooved
on one face. In ornithodelphous mammals the penial urethra
is complete, but open behind, and distinct from the genito-
urinary sinus. In the Didelphia tlie penial urethra and gen-
ito-urinary sinus are united into one tube, but the corpora
cavernosa are not directly attached to the ischium.

Certain Heptilia possess a pair of eversible copulatory or-
gans situated in integumentary sacs, one on each side of the
cloaca, but it does not appear in what manner these penes
are morphologically related to those of the higher Vertehrata,

In the female sex, the homologue of a penis frequently
makes its appearance as a clitoris, but rarely passes beyond the
stage of a grooved process with corpora cavernosa and corpus
spongiosum — the former attached to the ischium, and the lat-
ter developing a glans. But, in some few mammals (e. g., the
Lernuridce) , the clitoris is traversed by a urethral canal.

In no vertebrated animal do the ovaries normally leave the
abdominal cavity, though they commonly forsake their primi-
tive position, and may descend into the pelvis. But, in many
mammals, the testes pass out of the abdomen through the
inguinal canal, between the inner and outer tendons of the
external oblique muscle, and, covered by a fold of peritonaeum,
descend temporarily or permanently into a pouch of the integ-
ument — the scrotum. In their course they become invested
with looped muscular fibres, which constitute the cronaster.
The cremaster retracts the testis into the abdominal cavity, or
toward it, when, as in the higher mammals, the inguinal canal
becomes very much narrowed or altogether obliterated. In
most mammals the scrotal sacs lie at the sides of, or behind,
the root of the penis, but in the Didelphia the scrotum is sus-
pended by a narrow neck in front of the root of the penis.

In most mammals the penis is enclosed in a sheath of in-
tegument, the preputium / and, in many, the septum of the
corpora cavernosa is ossified, and gives rise to an os penis.

In the female the so-called Idbiamajora represent the scro-
tal, the lahia minora the preputial, part of the male organ of
copulation.

Organs not directly connected with reproduction, but in
various modes accessory to it, are met with in many Y^erte-
hrata. Among these may be reckoned the integumentary
pouches, in which the young are sheltered during their devel-
opment in the male Pipefish i^Syngiiathus), in some female
Amphibia (Notodelp>hys, Pipd), and Marsupialia j together
with the mammary glands of the Mammalia^

CHAPTER ni.

THE IROVINCES OF THE VEBTEBHATA THE CLASS PISCES.

The Vertabrata are divisible into tbree primary groups or
provinces : the Ichthyopsida^ the Sauropsida^ and the MaiTir

■media.

I. — The Ichthyopsida

1. Have the epidermic exdskeleton either absent, or very
slightly represented.

2. The spinal column may persist as a notochord with a
membranous sheath, or it may exhibit various degrees of
chondrification or ossification. When the vertebrae are dis-
tinct, their centra have no epiphyses.

3. The skull may be incom23lete and membranous, more
or less cartilaginous, or osseous. When membrane bones are
developed in connection with it, there is a large parasphenoid.
The basisphenoid is always small, if it be not absent.

4. The occipital condyle may be absent, or single, or
double. When there are two occipital condyles they belong
to the ex-occipital region, and the basi-occipital region is un-
ossified or very imperfectly ossified.

5. The mandible may be absent, or be represented orAy by
cartilage. If membrane bones are developed in connection
with it, there is usually more than one on each side. The
articular element may be ossified or not, and may be con-
nected with the skull by the intermediation of a quadrate and
a hyomandibular element, or by a single fixed plate of carti-
lage representing both these and the pterygo-palatine arch.
A stapes may be present or absent.

6. The alimentary canal may or may not terminate in a
cloaca. When there is no cloaca, the rectum opens in front of
the urinary organs.

7. The blood-corpuscles are always nucleated, and the
heart may be tubular, bilocular, or trilocular.

THE SAUEOPSIDA. 101

8. There are never fewer tlian two aortic arclies in the
adult.

9. Respiration takes place by branchiae during part, or the
whole, of life.

10. There is no thoracic diaphragm.

11. The urinary organs are permanent Wolffian bodies.

12. The cerebral hemispheres may be absent, and are
nev^er united by a corpus callosum.

13. The embryo has no amnion, and, at most, a rudimen-
tary allantois.

14. There are no mammary glands.

II. — The Sauropsida

1. Almost always possess an epidermic exoskeleton in the
form of scales or feathers.

2. The centra of the vertebrce are ossified, but have no
terminal epiphyses.

3. The skull has a completely ossified occipital segment,
and a large basisphenoid. No separate parasphenoid exists
in the adult. The prootic is ahvays ossified, and either
remains distinct from the epiotic and opisthotic throughout
life, or unites with them only after they have anchylosed with
adjacent bones.

4. There is alwa^^s a single, convex, occipital condyle, into
which the ossified ex-occipitals and basi-occiptal enter in vari-
ous proportions.

5. The mandible is always present, and each ramus con-
sists of an articular ossification, as well as of several mem-
brane bones. The articular ossification is connected with the
skull by a quadrate bone. The apparent " ankle-joint" is situ-
ated, not between the tibia and the astragalus, as in all 3Iani-
inalia^ but between the proximal and the distal divisions of
the tarsus.

6. The alimentary canal terminates in a cloaca.

7. The heart is trilocular or quadrilocular. Some of the
blood-corpuscles are always red, oval, and nucleated.

8. The aortic arches are usually two or more, but may be
reduced to one, which then belons-s to the rioht side.

■ • • • ^

9. Respiration is never effected by means of branchire, but,
after birth, is performed by lungs. The bronchi do not branch
dichotomously in the lungs.

10. A thoracic diaphragm may exist, but it never forms
a complete partition between the thoracic and the abdominal
viscera.

i02 THE ANATOMY OF VEETEBRATED ANIMALS.

11. The AYolffian bodies are replaced, functionally, by per*
manent kidneys.

12. The cerebral hemispheres are never united by a corpus
callosum.

13. The reproductive organs open into the cloaca, and the
oviduct is a Fallopian tube, which presents a uterine dilata-
tion in the lower part of its course.

14. All are oviparous, or ovoviviparous.

15. The embryo has an amnion, and a large respiratory
allantois, and is developed at the expense of the massive
vitellus of the egg.

10. There are no mammary glands.

III. — The Mammalia

1. Always possess an ej)idermic exoskeleton in the form of
hairs.

2. The vertebrge are ossified, and (except in the ornitliO'
delphid) their centra have terminal epij)hyses.

3. All the segments of the brain-case are completely ossi-
fied. No distinct parasphenoid exists in the adult. Tiie prootic
ossifies, and unites with the epiotic and opisthotic before these
coalesce with any other bone.

4. There are always two occipital condyles, and the basi-
occipital is well ossified.

5. The mandible is always present, and each ramus con-
sists (at any rate, in the adult) of a single membrane bone,
which articulates wdth the squamosal. The quadrate bone,
and the supra-stapedial element of the hyoidean arch, are con-
verted into a malleus and an incus, so that, with the stapes,
there are, at fewest, three ossicula audiMs.

6. The alimentary canal may, or may not, terminate in a
cloaca. When it does not, the rectum opens behind the
genito-urinary organs.

7. The heart is quadrilocular. Some of the blood-cor-
puscles are always red and non-nucleated.

8. There is only one aortic arch which lies on the left side.

9. Respiration is never effected by means of branchia?, but,
after birth, is performed by lungs.

10. There is a complete diaphragm.

11. The Wolffian bodies are rejDlaced by permanent kidneys.

12. The cerebral hemispheres are united by a corpus cal-
losum.

13. The reproductive organs may, or may not, open into a
cloaca. The oviduct is a Fallopian tube.

THE CLASS PISCES. 103

14. The embryo lias an amnion and allantois.

15. Mammaiy glands supply the young with nourishment.

The Ichthyopsida. — Class I. — Pisces.

The class of Fishes contains animals which vary so much
in their grade of organization, and in their higher forms so
closely approach the Amphibia^ that it is difficult to draw up
any definition which shall be at once characteristic and diag-
nostic of them. But they are the only vertebrated animals
which possess median fins supported by fin-rays ; and in
which the limbs, when present, do not exhibit that division
into brachium, antebrachium, and manus, which is found in all
other Vertebrata.

The presence of the peculiar integmentary organs con-
stituting what is known as the system of mucous canals and
the organs of the lateral line {suj^ra, p. 79 ), is highly charac-
teristic of Fishes, though these organs cannot be said to exist
m the entire class.

The class Pisces is divisible into the following primary groups :
A. The notochord extends to the anterior end of the body. There are no
skull, brain, auditory, or renal organs, such as exist in the higher Verte-
hrata. The heart is a simple tube, and the liver is saccular. (Lepto-
CARDiA. Haeckel.)

I. — PharyngohrancJiii.

B The notochord ends behind the pituitary fossa. A skull, brain, auditory,
and renal organs are developed. The heart is divided into auricular and
ventricular chambers. The liver has the ordinary structure. (Pachy-
CARDIA. Hck.)

a. The nasal sac is single, and has a median external aperture. Neither

mandibles nor limb arches are developed. {Monorhina. Hck.)

II, — Ifccrsipobranchfi.

b. There are two nasal sacs with separate apertures. Mandibles and

limb arches are developed. {Amphirhina. Hck.)
or. The nasal passages do not communicate with the cavity of the
mouth. There are no lungs, and the heart has but one auricle,
a. The skull is devoid of membrane bones.

III. — Elasmobranchil.

p. Membrane bones are developed in relation with the skull.

1. The optic nerves fovm a chiasma, and there are seyeral

rows of valves in the aortic bulb.

IV. — Ganoidei.

2. The optic nerves simply cross, and there is only one

row of valves in the aortic bulb.

V. — Teleostei.
b. The nasal passages communicate with the oral cavity. Therf
are lungs, and the heart has two auricles.

VI. — Dipnoi.

104

THE ANATOMY OF VERTEBRATED ANIMALS.

I. The PHARY]srGOBRA:N^CHn. — This order contains but one
species of fish, the remarkable Lancelet, or Am^^hioxus lanceo-
latus, which lives in sand, at moderate depths in the sea, in
many parts of +he world. It is a small, semitransparent crea-
ture, pointed at both ends, as its name implies, and possessing
no limbs, nor any hard epidermic or dermal covering-.

The dorsal and caudal regions of the body present a low
median fold of integument, which is the sole representative of
the system of the median fins of other fishes. The mouth
(Fig. 28, A, a) is a proportionally large oval aperture, which
lies behind, as well as below, the anterior termination of the
body, and has its long axis directed longitudinally. Its mar-
gins are produced into delicate ciliated tentacles, supported by
semi-cartilaginous filaments, which are attached to a hoop of the
same texture placed around the margins of the mouth (Fig.
29,/",^). These probably represent the labial cartilages of
other fishes. The oral aperture leads into a large and dilated
pharynx, the walls of which are perforated by numerous

Fig. 28. — AmpJdoxus lanceolatus. — a, mouth; 5, pliar}Tijrobranchial chamber; c, anus;
d, liver; «, abdominal pore. — B, the head enlarged ; o, the notochord ; b, the represent-
atives of neural spines, or fin-rays; c, the jointed oral ring ; (f, the filamentary append-
ages of the mouth ; e, the cihated lobes of the ijharj'iix ; /; gr, part of the branchial sac ;
A, the spinal cord.

clefts, and richly ciliated, so that it resembles the pharynx of
an Ascidian (Fig. 28, B, /*, g). This great pharynx is con
nected with a simple gastric cavity which passes into l

THE PHARYNGOBRANCni.

105

straight intestine, ending in the anal aperture, wbich is situ-
ated at tlie root of the tail at a httle to the left of the me-
dian line (Fig. 28, A, c). The mucous membrane of the in-
testine is ciliated.

An aperture called the abdominal pore (Fig. 28, A, e),
placed in front of the anus, leads into a relatively spacious
cavity, which is continued forward, on each side of the
pharynx, to near the oral aperture. The water which is con-
stantly propelled into the pharynx by its cilia, and those of
the tentacles, is driven out through the branchial clefts, and
makes its exit by the abdominal pore.

The liver (Fig. 28, A, d) is a saccular diverticulum of the
ntestine, the apex of which is turned forward.

""iG. 29. — Anterior end of the body of AmpMovn^. — C%, notochord; My, myelon, t>r spinpj
chord ; «, position of olfactory (?) sac; &, optic nerve ; c, fifth (?) pau-; f7, fepinal nerves ;
e, representatives of neural spines, or fin-i-ays ; y, gr, oral skeleton. The lighter and
darker shading represents the muscular segments and their interspaces.

The existence of distinct kidneys is doubtful ; and the re-
productive organs are simply quadrate glandular masses,
attached in a row, on each side of the walls of the visceral
cavity, into which, when ripe, they pour their contents.

The heart retams the tubular condition w^hich it possesses
in the earliest embryonic stage only, in other T^ertehrata.
The blood brought back from the body and from the ali-

106 THE ANATOMY OF VERTEBRATED ANIMALS.

mentary canal enters a pulsatile cardiac trunk, wliich runs
along the middle of the base of the pharynx, and sends
branches up on each side. The two most anterior of these
pass directly to the dorsal aorta ; the others enter into the
ciliated bars which separate the branchial slits, and, therefore,
are so many branchial arteries. Contractile dilatations are
placed at the bases of these branchial arteries. On the dorsal
side of the pharjmx the blood is poured, by the two anterior
trunks, and by the branchial veins -which carry away the
aerated blood from the branchial bars, into a great longi-
tudinal trunk, or dorsal aorta, by which it is distributed
throughout the body.

Notwithstanding the extremely rudimentary condition of
the liver, it is interesting to observe that a contractile trunk,
which brings back the blood of the intestine, is distributed on
the hepatic sac after the manner of a portal vein. The blood
IS collected again into another contractile trunk, which repre-
sents the hepatic vein, and is continued into the cardiac trunk
at the base of the branchial sac. The corpuscles of the blood
are all colorless and nucleated.

The skeleton is in an extremely rudimentary condition, the
spinal column being represented by a notochord, which extends
throughout the whole length of the body, and terminates, at
each extremity, in a point (Fig. 28). The investment of the
notochord is wholly membranous, as are the boundary- walls of
the neural and visceral chambers, so that there is no appearance
of vertebral centra, arches, or ribs. A longitudinal series of
small semi-cartilaginous rod-like bodies, which lie above the
neural canal, represent either neural spines or fin-rays (Fig.
28, B, h). Neither is there a trace of any distinct skull, jaws,
or hyoidean apparatus ; and, indeed, the neural chamber, wdiich
occupies the place of the skull, has a somewhat smaller capacity
than a segment of the spinal canal of equal length.

There are no auditory organs, and it is doubtful if a ciliated
sac, which exists in the middle line, at the front part of the
cephalic region (Fig. 29, a), ought to be considered as an olfac-
tory organ.

The myolon traverses the whole length of the spinal canal,
and ends anteriorly without enlarging into a brain. From
its rounded termination nerves are given off to the oral region,
and to the rudimentary eye or eyes (Fig. 26, h, c).

According to M. Kowalewsky,* who has recently studied

* "Memoires de I'Academie Imp6riale dea Sciences de St. Petersburg,"
1867.

THE PHARYNGOBRANCHIl. io7

the development of A.mp7uoxus, the vitellus undergoes com-
plete segmentation, and is converted into a hollow sphere, the
walls of which are formed of a single layer of nucleated cells.
The wall of the one moiety of the sphere is next pushed in, as
it Avere, until it comes into contact with the other, thus re-
ducing the primitive cavity to nothing, but giving rise to a
secondary cavity, surrounded by a double membrane. The
operation is, in substance, just the same as that by which a
double nightcap is made fit to receive the head. The blasto-
derm now accjuires cilia, and becomes nearly spherical again,
the opening into the secondary cavity being reduced to a small
aperture at one pole, which eventually becomes the anus.
M. Kow^alewsky points out the resemblance, amounting almost
to identity, of the embryo at this stage with that of many
Xtivertebixita.

One face of the spheroidal blastoderm becomes flattened,
and gives rise to lamincB dorsales, which unite in the charac-
teristically vertebrate fashion ; and the notochord appears
between and below them, and very early extends forward be-
yond the termination of the neural canal. The neural canal
remains in communication with the exterior, for a long time,
by a minute jDore at its anterior extremity. The mouth arises
as a circular aperture, developed upon the right side of the
anterior end of the body, by the coalescence of the two layers
of the blastoderm, and the subsequent perforation of the disk
formed by this coalescence. The branchial apertures arise by a
similar process which takes place behind the mouth ; and they
are, at first, completely exposed on the surface of the body. But,
before long, a longitudinal fold is developed upon each side, and
grows over the branchial apertures. The two folds eventually
coalesce on the ventral side, leaving only the abdominal pore
open. One cannot but be struck with the resemblance of these
folds to the processes of integument which grow over the bran-
chiae of the amphibian larva ; and, in like manner, enclose a cavi-
ty which communicates with the exterior only by a single pore.

In a great many of the characters which have been enu-
merated — as, for example, in the entire absence of a distinct
skull and brain, of auditory organs, of kidneys, of a cham-
bered heart ; in the presence of a saccular liver, of ciliated
branchiae and alimentary canal ; and in the extension of the
notochord forward to the anterior end of the body — Amphi-
axus dijBPers from every other vertebrated animal. Hence
Prof. Haeckel has proposed to divide the Vertebrata into
two primary groups — the Leptocardia^ containing Amphi-

108

THE ANATOMY OF VERTEBRATED ANIMALS.

oxus ^ and the PacJiycardia^ comprising all other Vercejrata.
The great peculiarities in the development of Amphioxus,
and the many analogies with invertebrate animals, particu-
larly the Ascidians, which it presents, lend much support to
this proposition.

No fossil form allied to A)n2^hioxics is known.

II. The Maesipobranciiii. — In this order of the class
Pisces the integument is devoid of scales or bony plates.

The spinal column consists of a thick persistent notochord
enveloped in a sheath, but devoid of vertebral centra. The
neural arches and the ribs may be represented by cartilages,
and there is a distinct si^ull presenting cartilage at least in its
base, and retaining many of the characters of the foetal cra-
nium of the higher Vertebrata. The notochord terminates in
a point in the base of this cartilaginous skull behind the pitui-
tary body ; and the skull is not movable upon the spinal col-

fio. 80. — A, the skull of a Lamprey, viewed from the side ; B, from above : — «, the ethmovo-
merine plate ; h, the olfactory oapsiilo ; c, the auditory capsule ; </. the neural arches of
the spinal column ; e, the i)alatopterypoid portion ; f, probably, the metapterypoid, or
Buporior quadrate, portion, and g, the inferior quadrate portion, of the sul>ocular arch ; /;,
otylohyal process; i. Ungual cartilage; ^•, inferior, lateral, prolongation of the cratii.sl
cartilage; 1, 2, 3, accessory labial cartilages; m, branchial skeleton. Thp. spaces ou
eltJier side of 1 are closed bv membrane.

THE MARSIPOBRANCmi. 109

ama. There are no jaws ; but the palatopterjgoid, the quad-
rate, the hyoraandibular, and the hyoidean apparatus of higher
Vertebrata, are imperfectly represented (Fig. 30, /*, g, h). In
some genera a basket-like cartilaginous apparatus strengthens
the walls of the oral cavity ; while, in others, such a framework
supports the gill-sacs.

The Mars'ipohranohil possess neither the pectoral nor the
pelvic pair of limbs, nor their arches. Horny teeth may be
developed upon the roof of the palate, or upon the tongue, or
may be supported by peculiarly developed labial cartilages.
The alimentary canal is simple and straight, and the liver is
not sac-like, but resembles that organ in other Vertehrata.

The heart has the usual piscine structure, consisting of a
single auricle preceded by a venous sinus, a single ventricle,
and an aortic bulb, all separated from one another by valves.
This heart is contained in a pericardium, the cavity of which
communicates with that of the peritonaeum.

In 3Iyxme the portal vein is rhythmically contractile.

The cardiac aorta, which is continued from the bulb, dis-
tributes its branches to the respiratory organs. These consist
of antero-posteriorly flattened sacs, which communicate directly
or indirectly, on the inner side, Avith the pharynx, and, exter-
nally, with the surrounding medium.

In the Lamprey there are seven sacs, upon each side, which
open externally by as many distinct apertures. Internally,
they communicate with a long canal, which lies beneath the
oesophagus and is closed behind, while anteriorly it communi-
cates freely with the cavity of the mouth (Fig. 32, Pr).

The kidneys are well developed, and have the ordinary ver-
tebrate structure, while the ureters open behind the rectum.

The brain, though very small, is quite distinct from the
myelon, and presents all the great divisions found in the high-
er Vertebrata — that is to say, a fore-brain, mid-brain, and hind-
brain. The fore-brain is further divided into rhinencephala,
solid prosencephalic lobes, and a thalamencephalon; the hind-
brain, into metencephalon and myelencephalon (Fig. 31).

The auditory organ is simpler than in other fishes, possess-
ing only two semicircular canals and a sacculated vestibule in
the Lamprey. In Myxine the whole organ is represented by
a single circular membranous tube, without further distinction
into canals and vestibule.

The Marsipobranchii differ remarkably, not only from the
fishes which lie above them, but from all other vertebrate ani-
mals, in the characters of the olfactory organ, which consists of

110

THE ANATOMY OF YERTEBRATED ANIMALS.

a sac placed in the middle line of the head, and having a sin-
gle, median, external aperture. In all other Vertehrata there
are two nasal sacs. In the Lampreys, the nasal sac terminates

Fis. 81. — Side and upper views of the brain of Petromyson flnmiatilU, and an upper and
inner view of the membranous labyrinth of P. marinus. The following letters refer to
the figures of the brain : I., the olfactory nerves, narrow anterior prolongations of th«
rhinencephalon (A); B. the prosencephalon; C, the thalamencei>halon ; I), the mesen-
cephalon ; E, the medulla oblongata ; F, the fourth ventricle ; e, the narrow band which
is all that represents the cerebellum ; G, the spinal cord ; II., the optic ; III., the oculo-
motorius ; IV., the patheticus ; V., the trigeminal ; VI., the abducens ; VII., the facial, and
the auditory; VIII., the glosso-pharyngeal and pneumogastric ; IX., the hypoglossal
nerves ; 1, i', 2, 2', sensory and motor roots of the first two spinal nerves. In" the figure
of the membranous labyrinth : k, the auditory nerve ; a, the vestibule ; c, the two semi-
circular canals, which coiTCspond with the anterior and posterior vertical canals of other
Vertebrata ; d, their union and common opening into the vestibule ; &, the ampullse.

blindly below and behind, but in the Hags {JSTyxine)^ it opens
into the pharynx. In no other fishes, except Lepidoslren^ does
the olfactory apjDaratus communicate with the cavity of the
mouth.

The reproductive organs of the Marsipohrancliii are solid
plates suspended beneath the spinal column, and they have no

THE ELASMOBRANCHII.

Ill

ducts, but shed their contents into the abdomen, whence they
pass out by an abdominal pore. In the early stages of their
development the Lampreys present some singular resemblances

Flo r<?,. — ^Vertical arivl longitixdinal section of the anterior part of the body of a Lamprey
yP^tramyzon maviiius): A, the cranium with its contained brain; a', section ol' the
ed^ of the cartilage marked a, in Fig. 30 ; Olf, entrance into the olfactorj' chamber,
wbii'.h is prolonged into the coecal pouch, o ; Ph, the pharynx ; Pr, the branchial chan-
nel, with the inner apertures of the branchial sacs ; Jf, the cavity of the mouth, with its
horcy teeth ; 2, the cartilage which supports the tongue ; 3, the oral ring.

to the AmpJiihia. They also undergo a metamorphosis, the
young Petromyzon being so unlike the parent, that it was, un-
til lately, regarded as a distinct genus — Ammocoetes, But
the young Lampreys never possess external branchial filaments
or spiracula.

The 3farsipohranchii are inhabitants of both fresh and salt
water. The Myxinoids are remarkable for their parasitic hab-
its — the Hag boring its way into the bodies of other fishes,
such as the Cod. No fossil Marsipobranchii are known. This
circumstance may, in part, be due to the perish ableness of
their bodies ; though horny teeth, like those of the Lampreys,
might have been preserved under favorable circumstances.

III. The Elasmobranchii. — This order contains the Sharks,
the Rays, and the Ghimmra.

The integument may be naked, and it never possesses scales
like those of ordinary fishes ; but, very commonly, it is devel-
oped into papillce, which become calcified, and give rise to
toothlike structures : these, when they are very small and close-
set, constitute what is called shagreen. When larger and more
scattered, they form dermal plates or tubercles ; and when, as
in many cases, they take the form of spines, these are called
dermal defences^ and, in a fossil state, ichthyodorulites. All
these constitute what has been called a '''' placoid exosJceleton ; "

112 THE ANATOMY OF YERTEBRATED ANIMALS.

and, in minute structure, they precisely resemble teeth, as has
been already explained. The protruded surfaces of the dermal
defences are frequently ornamented with an elegant sculptur-
ino", which ceases upon that part of the defence which is im-
bedded in the skin. The dermal defences are usually implanted
in front of the dorsal fins, but may be attached to the tail, or,
in rare cases, lie in front of the paired fins.

The spinal column exhibits a great diversity of structure :
from a persistent notochord exhibiting little advance upon that
of the Marsipohrancliii^ or having mere osseous rings devel-
oped in its walls, to complete vertebrae, with deep conical an-
terior and posterior concavities in their centra, and having the
primitive cartilage more or less completely replaced by concen-
tric, or radiating, lamella3 of bone. In the Rays, indeed, the
ossification goes so far as to convert the anterior part of the
vertebral column into one continuous bony mass.

The neural arches are sometimes twice as numerous as the
centra of the vertebrae, in which case the added arches are
termed intercrural cartilages.

The terminal part of the notochord is never enclosed with-
in a continuous bony sheath, or urostyle. The extremity of
the vertebral column is generally bent up, and the median fin-
rays which lie below it are, usually, much longer than those
wiiich lie above it, causing the lower lobe of the tail to be
much larger than the upper. Elasmobranchs with tails of
this conformation are truly heterocercal^ while those in which
the fin-rays of the tail are equally divided by the spinal col
umn, or nearly so, are diphy cereal (p. 21). The Monkfish
{Squatina) and many other Ekismohranchii are more diphy-
cercal than heterocercal.

The ribs are always small, and may be quite rudimentary.

The skull is composed of cartilage, in which superficial
pavement-like deposits of osseous tissue may take place, but
it is always devoid of membrane bone. When movable
upon the spinal column, it articulates therewith by two con-
dyles.

In its general form and structure, the cartilaginous skull
of an Elasmohranch corresponds with the skull of the verte-
brate foetus in its cartilaginous state, and there are usually
more or less extensive membranous fontanelles in its upper
walls. The ethmoidal region sends horizontal plates over the
nasal sacs, the apertures of which retain their embryonic situ-
ation upon the under-surface of the skull.

Neither premaxillae nor maxillae are present, the *' jaws ^'

THE ELASMOBRANCHIl.

113

of an Elasmobrancli consisting-, exclusively, of cartilaginous
representatives of the primary palato-quadrate arch and of
Meckel's cartilage.

The former of these, the so-called upper jaw, may either
be represented, as in the ChimcBra (Fig. 33), by the anterior
portion (^, D) of a triangular cartilaginous lamella, which
stretches out from the sides of the base of the skull, and is
continuous with the representative of the hyomandibular sus-
pensorium ; or there may be, on each side, a cartilaginous bar
inovably articulated in front with the fore-part of the skull ;
and, posteriori}'-, furnishing a condyle, with which the ramus
of the lower jaw, representing Meckel's cartilage, articulates.

In the latter case, which is that met with in the Sharks
and Rays (Figs. 34 and 35), a single cartilaginous rod {g) is
movably articulated with the skull, in the region of the peri-
otic capsule, upon each side ; and, by its opposite extremity,
is connected by ligamentous fibres both with the palato-
quadrate (A) and with the mandibular or Meckelian cartilage
{Mn). This cartilaginous siisj)e)isoriwn represents the hyo-

fiG. 83. — Vertical section of the skull of Chimcera monstrosa, -without the labial and nasid
cartilag-es: ^1, the basi-occipital region; P, the pituitary fossa ; iV^a, partition between
the olfactory sacs ; B, alveolus for the anterior upper-jaw tooth ; C, D, the region of th«
triangular cartilage which answers to the hyomandibular and quadrate ; D, B, that
which answers to the quadrate, pterygoid, and palatine ; J/>i, the mandible ; / Or, the
interorbital septum; asc and/>sc, the anterior and posterior semicircular canals; I., II.,
v., VIII., exits of the olfhctory, optic, fifth and eighth pairs of nerves.

mandibular and the symplectic bones of the Teleostel^ and
gives attachment to the hyoidean apparatus (-Sy). Tlie lat-

114 TBE ANATOMY OF VERTEBRATED ANIMALS.

ter consists of a lateral arch upon each side, united with its
fellow, and with the branchial arches, by the intermediation
of medial basal elements below ; and it is succeeded by a
variable number of similar arches, which support the branchial
apparatus.

From the hyoidean and from the branchial arches carti-
laginous filaments pass directly outward, and support the walls
of the branchial sacs. Superficial cartilages, which lie par-
allel with the. branchial arches, are sometimes superimposed
upon these. There are no opercular bones, though cartilagin-
ous filaments which take their place (Fig. 34, Op) may be
connected with the hyomandibular cartilage ; and, in the
great majority of the jElasmohranchii^ the apertures of the
gill-sacs are completely exposed. But in one group, the
Chimmra^ a great fold of membrane extends back from the
suspensorial apparatus, and hides the external gill-apertures.

Large accessory cartilages, called labial^ are developed at
the sides of the gape in many Mlasmohranchii. (Figs. 34 and

The pectoral arch consists of a single cartilage on each
side. The two become closel}^ united together in the ventral
median line, and are not directly connected with the skull.
The pelvis is also represented by a pair of cartilages, which
may coalesce, and are invariably abdominal in position.

There are always two pairs of lateral fins corresponding
with the anterior and posterior limbs of the higher 'Vertebrata.
The pectoral fins, the structure of which has already been de-
scribed, are always the larger, and sometimes attain an enor-
mous size relatively to the body.

In these fishes, teeth are developed only upon the mucous
membrane which covers the palato-quadrate cartilage and the
mandible. They are never implanted in sockets, and they
vary greatly in form and in number.

In the Sharks the}'' are always numerous, and their crowns
are usually triangular and sharp, with or without serrations
and lateral cusps. As a rule, the anterior teeth on each side
have more acute, the posterior more obtuse crowns. In the
Port Jackson shark {(Jestracion)^ however, the anterior teeth
are not more acute than the most obtuse teeth of the others,
while the middle teeth acquire broad, nearly flat, ridged
crowns, and the hindermost teeth are similar but smaller.
The Rays usually have somewhat obtusely-pointed teeth, but
in Myliohates^ the middle teeth have transversely-elongated,

THE ELASMOBRANCHII.

115

^•3 "3

<«••=' to

all

o-^'-S

.J

^ -9

a bi

8 --^

c:-^ .'

Ml

rCTS M

P +-»

.-pa

.2 tog

2g3

-5-^3

Td t,

S-3

^"^ c3

e .^0

..s^

'^^f'^^

-^ 3

M i 5^

fH

.^a Cm

Ka,®

,

r/s'

Sa-S
« a

o3«-a

34),
ital
nas

.tp-|^'

^■■^2

"O ^4

•S«o

^S C

^^^

+3 '3

a§i:

« a

•2 S >>

t» ^

, "^s

•S oi :i

•» ca

53 03 _

S S 3

^1-^

«„ t, .^

Pi®

r5

pa x3

^

1

i-^

si

^'€'^:

5h

^r '^^ +.S

Ol

eo^ t.

>>

*-« c3

c3

»• =>«

(h

p

and the lateral ones hexagonal, flat crowns, and the various
teeth are fitted closely by their edges into a pavement. In

116 THE ANATOMY OF YERTEBIIATED ANIMALS.

Aetohatis only the middle transversely elongated teeth remain.
In the Sharks and Rays the teeth are developed from papillse,
or ridges, situated at the bottom of a deep fold within the mu-
cous membrane of the jaw. The teeth come to the edge of
the jaw, and, as they are torn away or worn down by use,
they are replaced by others, developed, in successive rows,
from the bottom of the groove. No such successive develop-
ment takes place in the Ghiinmra.

As in other fishes, there are no salivary glands. The wide
oesophagus leads into a stomach which is usually spacious and
sac-like, but sometimes, as in Cldinmra^ may be hardly distinct
from the rest of the alimentary canal. No diverticulum filled
with air, and constituting a swimming-bladder, as in Ganoid
and many Teleostean fishes, is connected with either the oesoph-
agus, or the stomach, though a rudiment of this structure has
lately been discovered in some Elasmobranchs.

The intestine is short, and usually commences by a dilata*
tion separated from the stomach by a pyloric valve. This
duodenal segment of the intestine is usually known as the
Mursa Entiana. It receives the hepatic and pancreatic ducts,
and, in the foetus, the vitelline duct. Beyond this part, the
absorptive area of the mucous membrane of the small intes-
tines is increased by the production of that membrane into a
fold, the so-called spiral valve, the fixed edge of which usually
runs spirally along the wall of the intestine. In some sharks
[Carcharias, Galeocerdo) the fixed edge of the fold runs
straight and parallel with the axis of the intestine, and the
fold is rolled up upon itself into a cylindrical spiral.

The short rectum terminates in the front part of a cloaca,
which is common to it and the ducts of the renal and the re-
productive organs. The peritoneal cavity communicates with
that of the pericardium in front, and, behind, opens externally
by two ahdominal pores. The heart presents a single auricle,
receiving the venous blood of the body from a sinus venosus.
There is a single ventricle, and the walls of the aortic bulb con-
tain striped muscular fibres, and are rhythmically contractile,
pulsating as regularly as those of the auricle and ventricle.

The interior of the bulb exhibits not merely a single row
of valves at the ventriculo-bulbous aperture, but several other
transverse rows of semilunar valves, which are attached to the
walls of the bulb itself, and at its junction with the aorta.
These valves must be of great importance in giving full effect
to the propulsive force exerted by the muscular wall of the
bulb.

THE ELASMOBRANCniI.

117

In a good many Elasmobranchii tliere is a spiracle^ or
aperture leading into the cavity of the mouth, on the upper
Bide of the head, in front of the suspensorium. From this
aperture (wliich, according to the observations of Prof. Wy-

Fw. 86. — The aortic bulb of a Shark {Lamna), laid open to show the three rows of valves,

V, w, 'V, and the thick muscular wall, m.

man, is the remains of the first visceral cleft of the embryo),
as well as from the proper branchial clefts, long branchial fila-
ments protrude, in the foetal state. These disappear in the
adult, the respiratory organs of which are flattened pouches,
with traversely-plaited walls, from five to seven in number.
They open by external clefts upon the sides (Sharks and Chi-
mcera), or under-surface (Rays), of the neck, and, by internal
apertures, into the pharynx.

The anterior wall of the anterior sac is supported b\'' the
hyoidean arch-. Between the posterior wall of the first, and
the anterior wall of the second sac, and between the adjacent
walls of the other sacs, a branchial arch with its radiating car-
tilages is interposed. Hence the hyoidean arch supports one
series cf branchial plates or laminae; while the succeeding
branchial arches, except the last, bear two series, separated by
a septum, consisting of the adjacent walls of two sacs with the
iiiterposed branchial skeleton.

The cardiac aorta, a trunk which is the continuation of the
bulb of the aorta, distributes the blood to the vessels of these
sacs ; and it is there aerated by the water which is taken in at
the mouth and forced through the pharyngeal apertures, out-
ward.

118

THE ANATOMY OF VERTEBRATED ANIMALS.

The kidneys of the Elasmohranchii do not extend so far
forward as those of most other fishes. The ureters generally
become dilated near their terminations, and open by a common
urinary canal into the cloaca behind the rectum.

The brain is well developed. It usually presents a large
cerebellum, overlying the fourth ventricle, the side-walls of
which {corpora restlformia) are singularly folded (Fig. 37, A.^
a) ; and moderate-sized optic lobes, which are quite distinct
from the conspicuous thalamencephalon, or vesicle of the third

f\Q. 37. — The brain of the Skate {Raia batis). A. From above ; JB. A portion of the van-
tral asyject enlar<,'ed : s, the olfactory bulbs ; a, the cerebral hemispheres which are niiited
Id the middle line; Z/, the thalamencephalon ; c, the mesencephalon; (?, the cerebellum :
a a, the plaited bands formed by the corpora restiformia; I., II., IV., V., the cerebral
nerves of the corresponding' pairs ; / the medulla oblongata ; w, a blood-vessel. In B. :
ch, the chiasma of the optic nerves; A, the pituitary body; wand v vessels connectwl
with it; k, the saecvs vasculoeus ; /3, the pyramids of the medulla oblongata.

THE ELASMOBRANCHII. 119

v^entricle. The third ventricle itself is a relatively wide and
short cavity, which sends a prolongation forward, on each side,
into a large, single, transversely-elongated mass (Fig. 37, a),
which is usually regarded as the result of the coalescence of
the cerebral hemis23heres, but is perhaps, more properly, to be
considered as the thickened termination of the primitive en-
cephalon, in which the lamina terminalis and the hemispheres
are hardly dijfferentiated. The large olfactory lobes are usually
prolonged into pedicles, which dilate into great ganglionic
masses where they come into contact with the olfactory sacs
(Fig. 37, A.^ s). The latter ahvays open upon the under-sur-
face of the head. A cleft, which extends from each nasal aper-
ture to the margin of the gape, is the remains of the embryonic
separation between the naso-frontal process and the maxillo-
palatine process, and represents the naso-palatine passage of
the higher Vertehrata. The optic nerves fuse into a complete
chiasma (Fig. 37, JB.^ c/i), as in the higher Vertehrata. In
some Sharks, the eye is provided with a third eyelid or nictitat-
ing membrane, moved by a single muscle, or by two muscles,
arranged in a manner somewhat similar to that observed in
birds. In both Sharks and Rays, the posterior surface of the
sclerotic presents an eminence which articulates with the ex-
tremity of a cartilaginous stem proceeding from the bottom of
the orbit.

Except in Chimcera, the lab}rrinth is completely enclosed
in cartilage. In the Ra3's, the anterior and posterior " semi-
circular " canals are circular, and open by distinct narrow ducts
into the vestibular sac. In the other JE lasmohranchii they are
arranged in the ordinary way. A passage, leading from the
vestibular sac to the top of the skull, and opening there by a
valvular aperture, represents the canal by which, in the verte-
brate embryo, the auditory involution of the integument is at
first connected with the exterior.

The testes are oval, and are provided with an epididymis
and vas deferens, as in the higher Vertehrata, The vas def-
erens of each side opens into the dilated part of the ureter.
Attached to the ventral fins of the male are peculiar append-
ages, termed claspers.

The ovaria are rounded, solid organs. There are usually
two, but in some cases, as in the Dogfishes and nictitating
Sharks, the ovary is single and symmetrical. The oviducts
are true Fallopian tubes, which communicate freely with the
abdominal cavity at their proximal ends. Distally, they dilate
into uterine chambers, which unite and open into the cloaca.

120 THE ANATOMY OF VERTEBRATED ANIMALS.

The eggs are very large, and comparatively few.

The Dogfishes, the Rays, and the Chimmra^ are o\-iparouSj
and lay eggs, enclosed in hard, leathery cases ; the others are
viviparous, and, in certain species of 31ustelvs {Icevis) and Car-
charias^ a rudimentary placenta is formed, the vascular walls
of the umbilical sac becoming plaited, and interdigitating with
similar folds of the wall of the uterus.

The embryos of most Elasmobranchs are, at first, provided
with long external branchial filaments, which proceed from the
pcrijohery of the spiracle, as well as from most of the branchial
arches. These disappear, and are functionally replaced by
internal gills as development advances.

The Elasinobrmichii are divided into two groups, the Uolo-
cephali and the Plagiostomi,

In the Holocephali^ the palato-quadrate and suspensorial
cartilao^es are united with one another and with the skull into
a continuous cartilaginous plate ; the branchial clefts are cov-
ered by an opercular membrane. The teeth are very few in
number (not more than six, four of which are in the upper,
and two in the lower jaw, in the living species), and difi'er in
structure from those of the Plagiostomi. This sub-order con-
tains the living ChimcBra and Ccdlorhynehus, the extinct
Mesozoic JEdaphodon and Passalodon ; and, very probably,
some of the more ancient Elasmobranchs, the teeth of which
are so abundant in the Carboniferous limestones.

In the Plagiostomi, the palato-quadrate and suspensorial
cartilages are distinct from one another, and are movable upon
the skull. The branchial clefts are not covered by any oper-
cular membrane. The teeth are usuallv numerous.

The Plagivstonii are again subdivided into the Sharks
[Selachii or Squcdi), with the branchial apertures at the sides
of the body, the anterior ends of the pectoral fins not connected
with the skull by cartilages, and the skull with a median facet
for the first vertebra ; and the Rays (Iiajce), with the branchial
clefts on the under-surface of the body, the pectoral fins united
by cartilages to the skull, and no median articular facet upon
the occiput for the first vertebra.

The PJlasmohranchii are essentially marine in their habits ;
though Sharks are said to occur very high up in some of the
great rivers of South America.

Both divisions of the Plagiostomi occur in the Mesozoic
rocks. In the Palaeozoic epoch, dermal defences and teeth of
ILlasmohranchii abound in the Permian and Carboniferous

THE GANOIDEI. 121

formations, and are met with in the Upper Silurian rocks.
But, except in the case of JPleuracanthus (a Selachian), it is
impossible to be certain to what special divisions they belong.

lY. The Ganoidei. — In former periods of the world's his-
tory, this was one of the largest and most important of the
orders of fishes; but, at present, it comprises only the seven
genera — •Lepidosteus, Polypterus^ Calamoichthys, Ai7iia, Ac-
cipenser, Scapirhynchus, and Spatidaria, which are either par-
tially or wholly confined to fresh water, and are found only in
the northern hemisphere. These fishes differ very widely from
one another in many points of their organization, but agree in
the following characters, some of which they possess in com-
mon with the jElasmobranchii, and others with the Teleostei.
Thus :

a. The hullnis aortce is rhythmically contractile, and pro-
vided with several rows of valves, as in the JElasmobranchii,

b. The optic nerves unite in a chiasma, as in the JElastno-
branchii.

c. There is a well-developed spiral valve in the intestine,
as in the JE lasmobranchii^ in all but Lepidosteus, which pos-
sesses only a rudiment of such a valve.

On the other hand :

a. The branchial processes are not fixed throughout their
extent to the wall of a branchial sac, Avhich extends beyond
them, as in the Elasmobranchii / but their extremities project
freely beyond the edge of the septum which separates each
pair of branchial clefts, as in the Teleostei ; and, as in the
Teleostei^ they are covered by a bony operculum.

b. There is a large air-bladder connected by a permanently
Qi^Qw. pneumatic duct with the oesophagus, as in many Teleostei.

c. As in the Teleostei^ there is no cloaca.

The ventral fins are always abdominal in position. The
tail is diphycercal, or heterocercal, and the terminal portion
of the notochord is not ossified. The cavity of the abdomen
is placed in communication with the exterior by abdominal
pores. Finally, the ducts of the reproductive organs communi-
cate with those of the permanent urinary apparatus, which is,
in part, an Elasmobranch, in part, an Amphibian, character.

The exoskeleton presents the most extreme variations in
the Ganoidei. Spatularia is naked ; Accipenser and Scapi-
rhynchus develop numerous dermal plates composed of true
bone ; Amia is covered with overlapping cycloid scales ; Lepi'
dosteus and Polypterus have solid, rhomboidal, enamelled scales,
6

122

THE ANATOMY OF VERTEBRATED ANIMALS.

whicli not only overlap, but are fitted together by pegs and
Bockets, where their anterior and posterior edges come into
contact.

Fig. 38. — The brain of Lepidosteiis semiradiatus. A. From above; B. From below:/
the medulla oblongata ; (?, the cerebellum ; c, the oi)tic lobes of the mesencephalon ; y,
the cerebral hemispheres ; A, the pituitary bcdy ; «, the lobi inferiores. Ch, the chiaa-
ma ; I., olfactory ; II., optic nerves.

The endoskeleton is not less diversely modified ; and it is
worthy of remark that no sort of relation, either direct or
inverse, is traceable between the completeness of the endo-
skeleton and that of the exoskeleton. Thus Spatularia^
Scapirhynchus^ and Accipenser have a persistent notochord,
in the sheath of which mere cartilaginous rudiments of the
arches of vertebras appear. The ribs, when present, are par-
tially ossified. Polypterus and Amia have fully ossified ver-
tebrifi, the centra of which are amphiccelous. Lepklosteus also
has fully-ossified vertebra? ; but their centra are opisthocoe-
lous, having a convexity in front and a concavity behind, as in
some Amphibia.

More or fewer of the anterior vertebrae, or their cartilagi-
nous representatives, are united with one another, and ^vith
the posterior part of the skull. And the cranium may consist
principally of cartilage, membrane bones being superadded ;
or the primordial cartilage maybe largely superseded by bone,
as in the Teleostei,

Spatularia^ Scapirhynchus^ and Accipenser^ have skulls of
the former description. The cranium is one mass of cartilage,
continuous behind with the coalesced anterior spinal cartilages,
so as to be immovably connected with the spinal column. The
notochord enters its base, and terminates in a point behind
the pituitary fossa. In front, the cartilage is produced into a

THE GANOIDEI.

123

beak, wliicli, in Spatularia^ is very long, flattened, and spatu-
late. In the perichondium of the base of the skull, median
bones, answering to the vomer and to the parasphenoid of
Teieostean fishes, are developed ; and, in that of its roof, ossi-
'fications, which represent the parietals, frontals, and other
membrane bones of the Teleostei^ appear.

The framework of the jaws in Spatularia is very similar
to that in the JElasmobranchii. There is a partly cartilagi-
nous, and partly ossified, suspensorial cartilage \A, JB, Fig. 39),
which gives attachment below, directly, to the hyoidean arch
(S-l/), and, indirectly, to the jaws. The latter consist of a

All Ji&c

Or fjar, '_,-<^5=

Fig. 39. — Side-view of the skull of ^Spa^w^flrfai-wifh the beak cut away, and the anterior
(fisc)^ and posterior ( psc\ semicircular canals exposed : A%i,^ auditory chamber ; Or^
the orbit with the ej^e ; N, the nasal sac ; i/y, the hyoidean apparatus ; JSr, the repre-
sentatives of the branchiostegal rays ; 6>j9, operculum ; j)/n, mandible ; A^ B^ suspenso-
rium; i>, palato-quadrate cartilage; E^ maxilla.

palato-quadrate cartilage (7)) united by ligament with its fel-
low, and with the prefrontal region of the skull at F. / and
presenting, at its posterior end, a convex articular head to the
cartilage of the mandible, or Meckelian cartilage, Mn. It is
obvious that A^ JB, corresponds with the hyomandibular, or
suspensorial, cartilage in the Sharks and Rays ; D^ with the
palato-quadrate cartilage, or so-called " upper jaw," and the
cartilage of the mandible with the lower jaw in these animals.
But, in the Ganoid fish, an osseous operculum ( O}!) is attached
to the hyomandibular ; and a branchiostegal ray {J3r) to the
more strictly hyoidean part of the skeleton of the second vis-
ceral arch ; while a membrane bone (JE) representing tha
maxilla, and another {3In) the dentary, of the lower jaw in
Teleostei, are developed in connection with the palato-quadrate
and mandibular cartilages.

124

THE ANATOMY OF VERTEBRATED ANIMALS.

In the Sturgeon (Fig. 40), the membrane bones of the roof
of the skull are more numerous and distinct than in SjMtularia,
and large dermal bones (Z A'j JO) are united with them, to

Fig. 40. — The cartilai^inous skull of a Sturgeon, with the cranial bones. The former is
shaded, and supposed to be seen through the latter, which are left unshaded : a, ridge
formed by the spinous processes of the anterior vertebrae ; &, b, lateral winglike pro-
cesses; c, rostrum; Au, position of the auditory organ; A^a, position of the nasal sacs;
Or, that of orbit. The membrane bones of the upper surface are : A, the analogue of
the supra-occipital ; £, B, of the epiotics ; E, of the ethmoid ; 6r, G, of the postfrontals ;
U, H, of the prefrontals ; (7, C, the parietals ; Z>, i>, are the frontals, and F, F, the squa-
mosals ; JT, the anterior dermal scute ; /, /, and Z, Z, dermal ossilications connecting tba
j^^'ctoral arch with the skull.

form the great cephalic shield. The suspensorium (y, g^ A,
Fig. 41) is divided into two portions, to the lower of which
(at h) the proper hyoid is attached ; and the palato-quadrate

Fig. 41. — Side-view of the cartilaginous cranium of Accipenser: a, rostrum; 6, nasal
chamber ; Or, orbit ; c, auditory region ; d, coalesced anterior vertebrae ; e, ribs \f,g,\
BUfipensorium ; k, palato-maxillary apparatus ; Mn^ mandible.

cartilages, with their subsidiary ossifications, are so loosely
connected with the floor of the skull, that the jaws can be
protruded and retracted to a considerable extent.

In Lepidosteus^ Polypterus^ and A)nia, the skull presents
not only membrane bones, but, in addition, basi-occipital, ex-
occipital, and prootic ossifications of the primordial cartilage,
to which others may be added. The vomers are double, as in
the Amphibia (? JPolypterus). The apparatus of the jaws has
become modified in accordance with the Teleostean type of

THE GANOIDEI. 125

structure. The suspensoriura consists of two ossifications
united by a cartilaginous intermediate portion. The upper —
broad, and movably articulated with the periotic capsule — is
the hyomandibular j the lower answers to the symplectic of
osseous fishes. The cartilaginous palato-quadrate arcade is, in
part, replaced by a series of bones ; the palatine lies in front,
and is connected with the prefrontal region of the skull ; be-
hind it, lie representatives of the pterygoid, the metapterygoid,
the ectopterygoid ; and, most posteriorly, of the quadrate
bone. The last furnishes a condyle to the articular element
of the mandible. The symplectic is either loosely connected
with the quadrate, as in LepidosUus, or more closely united
with it, as in the other genera.

In Lepidosteus and Amia, a ctrcng and long membrane
bone, tliQ preojyercidiun^ is developed on the outer side of the
hyomandibular and quadrate bones, and connects them still
more firmly together.

The maxilla is represented by a series of small separate
ossifications in Lejndosteus. The proximal end of the man-
dibular cartilage ossifies, and becomes a distinct articular e, A
dentary element is added on the outer, and a splenial one
upon the inner side of the cartilage ; and in Lepidosteiis^ an-
gular, supra-angular, and coronary elements are added, so
that the components of the mandible are as numerous as in
reptiles. Lepidosteus and Amia have branchiostegal rays,
but Polypterus has none — at any rate, of the ordinary kind.
A ^va^Q jugular plate is developed between the rami of the
mandible in Amia, and there are two such plates in Polypterus^
which may possibly represent branchiostegal rays.

In Accipenser, Spaiularia, and Amia, the pectoral arch
presents two constituents : one, internal and cartilaginous,
answers to the cartilaginous pectoral arch of the JElasmo-
hrancliii, and to the scapula and coracoid of the higher IZer-
tebrata / the other, external, consists of membrane bones rep-
resenting the clavicular, supra-clavicular, and post-clavicular
bones of the Teleostei. In Lepidosteus one centre of ossifica-
tion appears in the cartilage ; in Polypterus, two. The upper
represents the scapula, and the lower the coracoid.

It has been already stated (p. 38) that PolypAerus comes
nearest to the Elasniohranchli in the structure of the rest of
the limb. The numerous dermal fin-rays, all nearly equal in
size, are connected with the rounded periphery of the broad
and elongated disk formed by the skeleton of the fin ; and the
Bcaly integument is continued to the bases of the fin-rays,

12G

THE ANATOMY OF VERTEBRATED ANIMALS.

vvbicli thus seem to fringe a lobe of the integument. Hence
the fin is said to be lohate. In the other genera, only two of
the basal cartilages are present, and some of the radialia
come into contact with the shoulder-girdle between them.
In addition, the anterior dermal fin-ray is much larger than the
others, and becomes directly connected with the anterior basal
cartilage. Thus, in the structure of their fins, as in so many
other characters, the Ganoldei are intermediate between the
Elasonohranchii and the Teleostei.

In certain Ganoids, as Lepidosteiis, Accipenser^ and many
fossil genera, the anterior margins of the anterior fin-rays of
the dorsal fins bear a single or a double series of small scales,
or spines, called fulcra.

In A.ccipenser and Polypterus^
spiracula^ or openings which com-
municate with the mouth, lie on the
top of the head, in front of the sus-
pensorium, as in many Elasmo-
branchs.

Lepndosteus^ Accipenser^ and ^cci'
pirhynclius^ have branchiee attached
to the hyoidean arch, as in the Elas-
tnobranddi. They are now called
opercular gills.

In Polypterus the air-bladder is
double and sacculated, and the pneu-
matic duct opens upon the ventral
aspect of the oesophagus. The air-
bladder thus becomes exceedingly
'like a lung; but its vessels are in
communication with those of the ad-
jacent parts of the body — not with
the heart, as in a true lung.

In Lepidosteus^ the ducts of the"

Fig. 42.— The female reproductive male and female reproductive organs

Sf open frds'ofte •■gSit^i ^^e Continuous with those bodies,

ducts; &, 6, oviducts; c, (7, the and each duct opcns into the dilated

rij,'ht and left divisions of the , r> •, • i t xi j.i r^

urinan- bladder; e, e, the open- ureter ot itS SIQC. \Vi the other Gra-

in{,'softhe ureters into the biad- ^oids the proximal cnds of the ffeni-

der;./, the anus; g, g, the ab- , .1 - &

doniinal pores ; A, the ui-ogenital tal duCtS, in DOtll SCXeS, Open Widely

^P'^'"^"''"- into the abdominal cavity. In Fo-

lypterus the united ureters open into
the cavity of the confluent oviducts, while, in the other Ga-
noids, the oviducts open into the dilated ureters. (Fig. 42.)

THE GANOIDEI.

127

When the fossil, as well as the existing Ganoidei^ are
taken into account, they form a large order, divisible into the
following sub-orders: 1 Amiadce, 2. Lepidosteidce^ 'd. Grosso-
pterygidce, 4. Ghondrosteidce, all of which have li\nng repre-
sentatives ; while the other three — viz., 5. Gephalasjndm^ 6.
Placodermi^ and 7. A.cantJiodldoe — have been extinct since
the Palaeozoic epoch, and are only ranged among the Ganoids
provisionally, inasmuch as we have no knowledge of their in-
ternal anatomy.

1. The Amiadce have a single living representative in the
rivers of North America — Amla calva ^ and it is not certain
that any member of the group occurs in the fossil state. The
cycloid scales, preoperculum, single median jugular plate,
branchiostegal rays, non-lobate paired fins, and heterocercal
tail, diagnose the sub-order.

2. The Lepidosteidce have rhomboidal enamelled scales, a
preoperculum, branchiostegal rays, non-lobate paired fins, and
heterocercal tail. These are represented in the rivers of
North America at the present day, and in tertiary formations,
by Lejndosteus j in the Mesozoic rocks, by a great variety of
genera — Lepidotus^ (Echrnodus^ Dapedlus^ etc. ; and, in the
Palseozoic epoch, by Paleonisciis in the Carboniferous, and
probably by Ghelrohpis^ in the Devonian, formation.

3. In the Grossopterygid(B the scales vary in thickness and
ornamentation, and may be thin and cycloid, or thick and

Fig. 43. — Eestoration of HoloxAycMus.

or, if

rhomboiii The dorsal fins are either two in number,
single, very long, or multifid. The pectoral fins, and usually
the ventrals, are lobate ; they are sometimes rounded, as in
.Polypterus — sometimes greatly elongated and almost filiform,
as in irolop*,ychius (Fig. 43). There are no branchiostegal
rays, but two principal, and sometimes many smaller lateral,

123 THE ANATOMY OF YEETEBRATED ANIMALS.

jugular plates. The tail may be either diphjcercal or lietero-
cereal.

The only living representatives of this sub-order are Polyp-
ferus and Calamoichthys, which inhabit the rivers of ISTorth
Africa. Neither of these are known to occur in the fossil state.
The only family of the sub-order at present known among
Mesozoic fossils is that of the GcelacantJdni, a remarkable
group of fishes with a persistent notochord, rudimentary ribs,
an air-bladder with ossified walls, and a single interspinous
bone for each of the two dorsal fins. The Ccelacanthini also
occur in the Carboniferous formation ; and the great majority
of the CrossopterygidcG are found in this and the Devonian
formations [Osteolejns^ Dlplopterus^ Glyptolcemus^ Megalich-
thys^ Soloptycliius^ Mhizodus^Dipteriis^ Phaneropleuron^ etc.).
Megalichthys^ Dipterus^ and probably a few other of these
fishes, have partially ossified vertebral centra ; the rest pos-
sessed a persistent notochord. It is by the CrossopterygidcB
that the Ganoids are especially connected with the Dipnoi^
and, through them, with the Amphibia.

4. The Chondrosteidce are either naked, or have dermal
plates of bone in the place of scales. Neither the pectoral nor
the ventral fins are lobate. The branchiostegal rays are few or
absent, the tail is heterocercal. There are no cartilage-bones in
the brain-case. The teeth are very small, or absent.

The Sturgeons {Acclpenser) — which inhabit the northern
rivers of Europe, Asia, and America, occasionally niigrating
to the sea — Spatularia^ and Scap)irhynchus (found in the rivers
of North America), are the recent members of this group,
which is represented, in the older Mesozoic rocks, by Glion-
drosteus.

5. The Ceplialasindm are remarkable fishes, probably allied
to the Chondrosteidce, which occur only in the Lower Devo-
nian and the Upper Silurian rocks, and are some of the oldest
fish at present known. The head is covered by a continuous
shield, which has the structure of true bone, in Cephalaspis^
but more resembles certain piscine scales, in Pterapsis. The
shield is prolonged into two horns at its posterolateral angles,
and a median dorsal backward prolongation usually bears a
spine, in Cephcdaspis / the body is covered with flat bony
scales or plates, and possesses two large pectoral fins. The
characters of the body and fins of Pier apsis are unknown.
Notwithstanding the excellent preservation of many of the
specimens of these fishes, they have, as yet, yielded no evi-
dence of jaws or teeth. Should jaws be absent, the Cepha'

THE GANOIDEI. 129

lasjndce ^yould approach the 3fars2pohranchii more nearly than
any of the other amphirhine fishes do.

6. The Placodermi^ comprising the genera Coccosteus^
Pter'ichtliys^ Asterolepis, and some others, are known to occur
only in the Devonian and Carboniferous formations. In these
fishes the pectoral region of the body is encased in great bony
plates, which, like those of the skull, are ornamented with
dots of enamel. The caudal reo'ion was covered with small
scales in PterichiJiys^ while in Coccosteus it appears to have
been naked. The pectoral member of JPterichthys is exceed-
ingly long, covered with suturally-united bony plates, and
united with the thoracic plates by a regular joint. In Coccos-
teus the pectoral member seems to have had the ordinary con-
struction. The bones of the head and thorax of Coccosteus
nearly resemble those of certain Siluroid fishes (e. g., Cla7'ias)
in their form and arrangement, and it seems probable that the
Placoderini were annectent forms between the physostome
Teleostei and the Ganoidei.

7. The Acanthodidce, on the other hand, seem to have con-
nected the Ganoidei with the IiJlasinobranchii. The scales
of these fishes of the Devonian and Carboniferous formations
are very small, and similar to shagreen ; spines, resembling the
dermal defences of the Elcismohranc^i^ are placed in front
of more, or fewer, of the median and of the paired fins. The
skull appears to have been unossified, and the pectoral arch
seems to have consisted of a single bony hoop.

The Pycnodontidce^ which are commonly grouped among
the Ganoids, are fishes with much-compressed bodies, like the
John Dory or the Filefishes, covered with large rhomboidal en-
amelled scales, from which bony ridges projected internally,
and were imbedded in the integument. The notochord is per-
sistent, but the neural arches and the ribs are ossified. The
proximal ends of the ribs, imbedded in the sheath of the noto-
chord, are but little expanded in the more ancient members
of the group, while, in the more modern species, they enlarge,
and at length unite by serrated sutures, giving rise to spurious
vertebras. The skull is high and narrow, as in JBalistes j the
premaxill^e are small, and there are no teeth in the maxilla?,
but several longitudinal series of crushing teeth (the vomer
and parasphenoid ?) are attached to the base of the skull.
These bite between the rami of the mandible, w^hich are also
armed w^ith several rows of similar teeth. The teeth of the
Pycnodonts have no vertical successors. The pectoral fins are
small, the ventral, obsolete. The Pycnodonts are all extinct,

130 THE ANATOMY OF YERTEBRATED ANIMALS.

but existed, formerly, for a very long period of time — tbeii
fossil remains occurring in rocks from the Carboniferous to the
older Tertiary formations, inclusively. They present curious
features of resemblance to the plectognath Teleostei.

The remains of Ganoid fishes began to appear in the Upper
Silurian rocks at the same time as those of the Elasmobranchii^
with which they constitute the oldest Vertebrata Fauna ; they
abound in the Devonian formation, and constitute, with the
Elasinohranchii^ the whole of the Palaeozoic Fish Fauna.
We are in io;norance of the true affinities of lliarsis and
27irissdps, and of the Soplopleuridoe / but unless some, or all,
of these are Teleosteans, Ganoids and Elasmobranchs, alone,
constitute the Fish Fauna of the Mesozoic formations, as far
as the bottom of the Cretaceous series.

V. The Teleostei. — The osseous fishes are occasionally de-
void of any exoskeleton. Sometimes they present scattered
dermal plates of true bone ; or, as in the Trunkfishes ( Ostra-
cio?i), the body may be encased in a complete cuirass, which is
calcified, but has not the structure of bone. Again, as in the
Filefishes (J3aUstes), the skin may be beset with innumerable
small spines, somewhat like those which form the shagreen of
the Elasmobranchs in appearance, though they differ from them
in structure. But, usually, the exoskeleton of the Teleosteans
takes the form of overlapping scales, which rarely exliibit the la-
cunae characteristic of true bone. The free portions of the
scales are sometimes smooth, and rounded at the edge, when
they are termed cycloid ^ or they are roughened with ridges
and minute spines, when they are called ctenoid.

The spinal column always presents ossified vertebral cen-
tra, and the primordial cartilage of the skull is more or less
replaced by bone. The centra of the vertebrge are usually bi-
concave, each face presenting a deep conical hollow. In cer-
tain Eels {Symbra7ichus)^ the centra of most of the vertebrae
are flat in front and concave behind, the most anterior pos-
sessing a convexity in front. In many Siluroid fishes a cer-
tain number of the anterior vertebrae are anchylosed togetlier,
and with the skull, into one mass, as in the Ganoids.

The vertebrae are distinguishable only into those of the
trunk and those of the tail. The latter are provided with com-
plete inferior arches traversed by the caudal artery and vein.
The former usually possess ribs, but these do not unite with
one another, nor with any sternum, in the ventral median line,
and they enclose the thoracico-abdominal viscera. The ver«

THE TELEOSTEI. 131

tebrae are commonly united by zygapophyses, or oblique pro-
cesses, placed above the centra ; in addition to which, the
lower margins of the centra are, not unfrequently, united by
additional articular processes. Transverse processes common-
ly exist, but the ribs are articulated with the bodies of tlie
vertebne, or with the bases of the transverse processes, not
with their extremities.

When a dorsal fin exists in the trunk, its rays are articu-
lated with, and supported by, elongated and pointed bones —
the interspinous bones, which are developed around preexist-
ing cartilages, and lie between, and are connected with, the
spines of the vertebrse. The fin-rays may be entire and com-
pletely ossified, or they may be transversely jointed and lon-
gitudinally subdivided at their extremities. Not unfrequentl}^,
the articulation between the fin-rays and the interspinous bone
is efi"ected by the interlocking of two rings — one belonging to
the base of the fin-ray and its included dermal cartilage, and
the other to the summit of the interspinous bone — like the
adjacent links of a chain.

In all Teleostean fishes the extremity of the spinal column
bends up, and a far greater number of the caudal fin-rays lie
below than above it. These fishes are, therefore, strictly
speaking, heterocercal. Nevertheless, in the great majority
of them (as has been already mentioned, page 19), the tail
seems, upon a superficial view, to be symmetrical, the spinal
column appearing to terminate in the centre of a wedge-shaped
hypural bone, to the free edges of which the caudal fin-rays
are attached, so as to form an upper and a lower lobe, which
are equal, or subequal. This characteristically Teleostean
structure of the tail-fin has been termed homocercal — a name
which may be retained, though it originated in a misconcep-
tion of the relation of this structure to the heterocercal con-
dition.

In no Teleostean fish is the bent-up termination of the
notochord replaced by vertebras. Sometimes, as in the Sal-
mon (Fig. 6, page 20), it becomes ensheathed in cartilage, and
persists throughout life. But, more usually, its sheath be-
comes calcified, and the urostyle thus formed coalesces with
the dorsal edge of the upper part of the wedge-shaped hypural
bone, formed by the anchylosis of a series of ossicles, which are
developed in connection with the ventral face of the sheath of
the notochord.

In the caudal region of the bodj^, interspinous bones are
developed between the spines of the inferior arches of the ver*

132

THE ANATOMY OF YERTEBKATED ANIMALS.

tebrse, and bear the fin-rays of the anal, and, in part, of the
caudal fin.

The Teleostei differ very much in the extent to which the
primordial cranium persists throug-hout life. Sometimes, as
in the Pike (Figs. 44 and 45), it grows with the growth of the

A

a;s. J3S Fro.

Fig. 44. — The cartilaginous cranium of the Pike {Esox Ivcius^, with its intrinsic ossifica-
tions; viewed. A, from above; B, from below; C, from the left, side: iV, N^ nasai fossa?;
/. Cr, interorbital septum; a, groove for the median ridge of the parasphenoid ; h^ canal
for the orbital muscles. Sq., wrongly so marked, is the Ftcrotic. V. and VIII. mark
the exits of the fiith and pneumogastric nerves ; 3, 3, small ossifications of the rostrum.

fish, and only becomes partially ossified ; in other cases it al-
most disappears. A basi-occipital {JB. 0.), ex-occipital (E. 0.),
and supra-occipital {/S. 0.) bone are developed in it, and form a
complete occipital segment. The proper basi-sphenoid {JBS)
bone is always a very small, and usually somewhat Y-shaped,
bone. The alisphcnoids {AS.) sometimes are and sometimes
are not developed. The presphenoidal and orbitosphenoidal
regions commonly, but not always, remain unossified.

In most osseous fishes, the base of the skull in front of the
'")asisphenoid is greatly compressed from side to side, and

THE TELEOSTEI.

133

forms an interorbital septum [Z. Or.).
the cranial cavity is consequently re-
duced to a comparatively narrow pas-
sage above the septum (t'ig. 45). In
the Siluroid and Cyprinoid fishes,
however, this septum is not formed,
and the cranial cavity is of nearly equal
size throughout, or gradually diminish-
ing forward. The ethmoidal cartilage
usually remains unossified, but Rome-
times, as in the Pike, ossifica,tion may
take place in it. (Fig. 44, 3, 3.) The
antorbital, or lateral ethmoidal, pro-
cesses of the primordial cranium os-
sify, and give rise to the prefrontal
bones [JPrf.). The postorbital pro-
cesses also ossify as postfrontals [Ptf.).
The upper and posterior part of the
primordial cranium exhibits five pro-
cesses — one postero-median, two pos-
tero-lateral, and two postero-external.
The postero-median ossifies as part of
the supra-occipital (>S. 0.). The pos-
tero-lateral ossifies as part of the epi-
otic {Ej). 0.), which lies upon the sum-
mit of the superior vertical semicircular
canal. The postero-external closely
corresponds with the squamosal of the
higher Vertebrata in position ; but, as
a cartilage bone, it corresponds with
an ossification of the capsule of the ear,
called pterotlc in the higher Vertebrata,
Not unfrequently, as in the Cod, for
example, the opisthotic ( Op. 0.) is a
distinct bone, and enters into the for-
mation of the postero-external process.
The prootic (^JPr.O.) is always a well-
developed bone, and occupies its regu-
lar place, in front of the anterior ver-
tical semicircular canal, and behind the
exit of the trigeminal nerve.

In addition to these cartilaore
bones, the brain-case of osseous fishes
is additionally defended by numer-

The anterior moiety of

Fig. 45. — Longitudinal and ver-
tical section of a fi-esh Pike's
skull. — The cut surface of car-
tilage is dotted. For S. V. C.
and P.V.C.^ read a.s.c.^ an-
terior, and 'p.s.G.y posterior
semicii'cular canal ; a, tha
parasphenoid ; y, the hasi-
sphenoid; Fo, the vomer
P., the pituitary fossa.

134 THE ANATOMY OF VERTEBRATED ANIMALS.

ous membrane bones. These are, on the roof of the
skull—

1. The parietal bones (-P«.), which sometimes meet in a
sagittal suture, as in most of the higher Vertebrata, but are
very generally separated by the juuction of the Jrontals with
the supra-occipital.

2. The large frontals {J^r.), which may or may not unite
into one.

3. The nasal bones (iV^rt.), apparently replaced in the Pike
by the bones 1 and 2.

Fig. 46. — Side and upper views of the skull of a Pike (Esox IvciiiFi)^ without the facial or
Bupra-orbital bones : y, the basisphenoid ; s, the ahsphenoid ; a, the articular facet for
the hyomandibular bone.

The under-surface of the skull possesses two membrane
bones: in front the voyner ( Fb.), and, behind, the huge para-
sphenoid (cc, £c), which ensheathes all the basis cranii^ from
the basi-occipital to the vomer.

A supra-orbital bone {S. Or.) is the only membrane bone
attached to the sides of the brain-case. Two premaxillary
bones {JPmx.) are attached, sometimes closely, sometimes
loosely, to the anterior extremity of the cranium ; and behind
these are the maxillae [3Ix.), which are sometimes large and
single, as in the Cyprinoid fishes, but may become subdivided,
or be reduced to mere styliform supports for cirri, as in many
Siluroid fishes. In most osseous fishes the maxilla take little
or no share in the formation of the gape, which is bounded
above by the backwardly-extended premaxilla3.

The palato-quadrate and hyomandibular have essentially
the same structure and arrangement as in Xepidosteus and

THE TELEOSTEL

135

Amia. The bomologue of the siispensorium of the JEJiasmo-
hranchii is articulated with a surface furnished to it by the
postfrontal, pterotic, and proOtic bones. Usually it moves

Ar AnSyPrO/x -Sro-

10 /I

Fig. 47.— Side-view of the skull of a Pike (^Esox licciu/i) : Prf. prefrontal ; IL 3/., hyoman-
dibular bono; Oj>, operculum; /S.Op., suboperculum ; I.Op, interoperculum; Pr, Op,
preoperculum ; Brr/, brunchiostcgal rays; Si/, syrai)lectic ; 3It, metii pterygoid ; P/,
palato-pterygoid arch ; Qu, quadrate bone ; J.>\ articular ; An, angular ; 2>, dentery ;
S.0/\ suborbital bone.

freely upon that surface, but, in the PlectognatJii^ it may be
fixed. It ossifies so as to p:ive rise to two bones : an upper
broad hyomancllbular (IL3I.)j with which the operculum artic-

FiG. 48.— Prdato-quadrate arch, with the hyomandibular and symplectic of the Pike, viewea
from the inner side; the articular piece {Art\ of the lower jaw, and Meckers cartilage
(Mck.) of the Pike ; seen from the inner side : a, the cartilage interposed between the
hyomandibular (iT". J/.), and the symplectic {Si/.); b, that which serves as a pedicle to
the pterygo-palatine arch ; c, process of the hyomandibular with which the operculum
articulates ; d, head of the hyomandibular which articulates with the skull.

ulates; and a lower styliform symjilectic (Sy.), which fits into
a groove on the inner and posterior surafce of the quadrate,
and is firmly held there.

The palato-quadrate arch is represented by several bones,
of which the most constant are the palatine {I^l.) in front, and

136 THE ANATOMY OF YERTEBRATED AXIMALS.

the quadrate {Qu.) beliind and below. Besides these there
may be three others: an external, ectopterT/goid (J^q^t.), an
internal, entoj^teiygoid (Ept.), and a inetapterygoid {Mpt.).
The last envelops the upper and posterior portion of the
primitive quadrate cartilage ; and, fixing itself against the
hyomandibular, contributes to the firmness of the union already
effected by the symplectic.

Meckel's cartilage [^fck.) persists throughout life, but the
ossification of its proximal end gives rise to an os articulare
in the lower jaw. To these an angular [An.) and a dentary
{D.) membrane bone are commonly added (Fig. 47).

The hyoidean arch is usually composed of two large cornua
— connected with the cartilaginous interval between the hyo-
mandibular and the symplectic by a stylohyal ossification, and
abutting, in the middle line below, upon one or more median
pieces, the anterior of which [entoglossal) supports the tongue,
while the posterior {urohyal) extends back to join the median
elements of the branchial apparatus. The cornua themselves
are usually ossified into four pieces : an upper {epiliyal) and a
lower {ceratohyal) large ossification, and two small ones {basi-
hycds) connected with the ventral ends of the lower large
ossification.

There are usually five pair of branchial arches connected
by median ventral ossifications. The posterior pair are single
bones, which underlie the floor of the pharynx, bear no bran-
chial filaments, but commonly support teeth, and are called
hypopharyngecd bones. In certain osseous fishes, thence
called Pharyngognathi, they anchylose together into one bone.
The anterior four pair are composed of several joints, and the
uppermost articulations of more or fewer of them usually
expand, bear teeth, and form the epipharyngeal bones. Sun-
dry important membrane bones are connected with the man-
dibular and hyoidean arches. The preoperculuni {P. Op.), op>er-
culmn (Oj).), and branchiostegal rays {Br.), already met with
among the Ganoidel, are the most constant of these. Beneath
the operculum, lies a suhopercidwn [S. Op.), and below this
an viteropercidu?n (Z Op.), which is connected by ligament
with the angular piece of the lower jaw, and is also united to
the outer face of the hyoidean arch. It may be altogether
ligamentous, as in the Siluroids.

The branchiostegal rays are attached partly to the inner,
md partly to the outer, surface of the hyoidean arch. They
Ripport a membrane, the branchiostegal membrane^ which
,;erves as a sort of inner gill-cover.

THE TELEOSTEI.

137

Most Teleostel possess two pair of limbs, the pectoral and
the ventral fins. But the latter are often absent, and the
former are occasionally wanting. When the pectoral fins are
absent, the pectoral arch usually remains, though it may be
reduced to little more than a filament, as in MiLrcenopMs,
The ventral fins are frequently situated in their normal posi-
tion beneath the posterior part of the trunk ; but in consider-
able groups of these fishes they are immediately behind the
pectoral fins {tlioracic)^ or even in front of them (jugular),
in the asymmetrical JPleuronectidcB one pectoral fin may be
larger than the other, or may alone remain, as in JSIonochlriis.

The pectoral arch always consists of a primarily cartila-
ginous coraco-sccqjular portion — which usually ossifies in tAvo
pieces, a coracoid below, and a scapula above — and of sundry
membrane bones. The chief of these membrane bones is the
clavicula ( Gl.)^ which meets its fellow in the middle line, and
is usually joined to it by ligament, but sometimes, as in the

ria, 49. — The bones of the pectoral arch and fore-limb of the Pike {Esov hiciiis): A, a
semi-diagrammatic view of these bones, to show their relative natural position. The
clavicle {CI) is supposed to be transparent. S.cl, supra-clavicula; p.cl, post-clavicula'
c, d, the posterior and anterior ends of the outer margin of the scapulo-coracoid. — B, the
scapulo-coracoid and hmb separate and on a larger scale ; Sep, scapula ; Ci\ coracoid ;
a, basal cartilages ; &, fin-rays ; c, corresponds with c in the foregoing figure.

138 THE AXATOMY OF VERTEBRATED ANIMALS.

Siluroids, by sutural union. By its inner surface it gives
attachment to the coraco-scapular — and sometimes above
them, to a styliform bone which extends back among the
lateral muscles — the 2^ost-clavicula {2:>.cl.).

Attached to the dorsal end of the clavicle, there is usually
a second much smaller bone, the siqyra-clavicula {/S.cl.), and
this is very generally connected with the skull by a superficial
membrane bone, the 2^ost-temporal, which, in front, becomes
forked, and attaches itself by one prong to the epiotic bone,
by the other to the pterotic, or lower down to the side of the
cranium. The base of the fin contains a series of not more
than five, more or less ossified, cartilages, which are placed
side by side and articulate with the coraco-scapular ; to these
succeed one or more rows of small cartilages, partially hidden
by the bases of the exoskeletal fin-rays. The most anterior
of these basal cartilages (the mesopterj-gial basale) is enclosed
by the base of the anterior fin-ray, and effects that articulation
with the shoulder-girdle which is so remarkable in many Silu-
roid fishes. The posterior cartilage, or bone, is the metaptery-
gial basale, and the intermediate three are radialia (p. 39),

Most Teleostei possess teeth, and, in the majority of these
fishes, teeth are very widely distributed over the surface of
the walls of the oral and pharyngeal cavities. The teeth vary
very much in structure ; ordinarily, they consist of dentine,
capped with structureless enamel. The parietes of the tooth
are not unfrequently longitudinally folded toward the base,
but this folding never goes so far as in the Ganoids. The dif-
ferent kinds and modes of arrangement of the teeth may be
classified as follows :

1. Isolated, more or less pointed teeth, developed from
papillae of the mucous membrane, which do not become en-
closed in sacs — frequently anchylosed to the subjacent bone,
but not imbedded in alveoli, nor replaced verticallj^ The great
majority of ordinary osseous fishes have teeth of this kind.

2. Isolated teeth, which become imbedded in sockets, and
are replaced vertically.

Such teeth are seen in the i:)rcmaxill9e of Sargiis, where
they curiously simulate the form of human incisors ; and, im-
bedded in the coalesced hypopharyngeal bones, in Lahms.

3. Isolated teeth, imbedded in the substance of the bone
which supports them. The teeth and the supporting bone
vvear away in front, and are replaced by new teeth developed
behind the others. This structure is seen in the coalesced
hj^popharyngeal bones of the Parrotfish {Scarui).

THE TELEOSTEI. I39

4. Beak-like compound teeth, attacked to the premaxillse
Mid dentary bones of the mandible.

These are of two kinds. In the Parrotfisb [Scarus) the
beak is formed by the union of numerous separately-developed
teeth into one mass. But in the Gymnodonts {Tetrodon and
Diodori) the beak is produced by the coalescence of broad
calcified horizontal lamellae thrown off from a subjacent pulp.

5. In the Carp and its allies the basi-occipital sends down
a median process, which expands at the end, and supports a
broad, thick, horny tooth.

The stomach is usually wide and sac-like, but sometimes
(in SQomheresoces, Cyprinoids, and others) is not wider than
the intestine. Occasionally, as in Mugil^ it acquires thick
walls and becomes gizzard-like. The commencement of the
small intestine is very generally marked by the presence of
more or less numerous csecal diverticula, the pyloric cceca.
The small intestine has no spiral valve, though the mucous
m.embrane may be raised into large transverse folds. The rec-
tum does not terminate in a cloaca, and almost always opens
quite separately from the urinary and genital ducts, and in
front of them.

In many Teleostean fishes an air-bladder underlies the ver-
tebral column, and is connected by an open pneumatic duct
with the dorsal wall of the oesophagus, or even with the stom-
ach, as in the Herring. In otiier Teleostei^ the air-bladder oc-
cupies tlie same position, but is closed, the duct by which the
air-bladder is primitively connected with the alimentary canal
becoming obliterated. In a comparatively small number of
the Teleostei — the JBlennii^ the Pleuronectidce or Flatfishes,
the Sand-eel (Ammodi/tes)^ the Loricarini^ and Symhranchii^
and some members of other families — there is no air-bladder.
In those Teleostei in which it is present, it may be divided into
two parts by a constriction ; or it may be prolonged into di-
verticula ; or o^etia tnirabilia may be developed in its walls.
Sometimes the air-bladder is brouo-ht into direct relation with
the membranous labyrinth, as in Myripristis and Sparus^ and
the Herring, Shad, and Anchovy — prolongations of the one or-
gan being separated from the other only by a membranous
fenestra in the wall of the skull. In the Siluroidei^ Gypri-
noidei^ and Gharacini^ and in the Gymnotini, the anterior
end of the air-bladder is connected with the membranous vesti-
bule by the intermediation of a series of bones attached to the
vertebral column, some of which are movable.

The vessels of the air-bladder are derived from, and empty

140 THE ANATOMY OF VERTEBRATED ANIMALS.

themselves into, those of the adjacent parts of the body, in
which respect, and in the dorsal position of the oesophageal
aperture of the pneumatic duct, this structure differs from a
lung.

The heart consists of a single auricle, receiving its blood
from a venous sinus ; and of a single ventricle, separated by a
single row of valves from the hulbus aortce^ which is not rhyth-
mically contractile.

The cardiac aorta divides into trunks to form the branchial
arteries, which run upon the outer, or convex, side of the bran-
chial arches, and are distributed to the branchial filaments.
The blood is collected thence into a branchial vein, which also
lies on the convex side of the arch ; and, increasing tow^ard its
dorsal end, opens into one of the trunks of the original dorsal
aorta. Of these there are two, a right and a left, which pass
backward and meet in the trunk of the dorsal aorta under the
spinal column.

The anterior branchial vein gives off, at its dorsal termina-
tion, a considerable carotid trunk, w^iich passes forward under
the base of the skull ; and this is united wdth its fellow by a
transverse branch — so that a complete arterial circle, the cir-
cuius cephalicus^ is formed beneath the base of the skull. Be-
low, the anterior branchial vein gives off the hyoidean artery,
which ascends along the hyoidean arch, and very generally
terminates by one branch in the cephalic circle, and by another
enters a rete mirahlle^ which lies in the inner side of the hyo-
mandibular bone, and sometimes has the form of a gill. This
is the pseudohranchia. The branches of the rete mircibile
unite again into the ophthalmic artery, which pierces the scle-
rotic, and breaks up into another rete mirabile^ the choroid
gland^ before being finally distributed.

In the Lamprey, as has been seen, tlie respiratory organs
are pouches, the anterior and posterior avails of which are
raised into vascular folds. The w^alls of adjacent pouches are
distinct and but loosely connected together ; and considerable
spaces of integument separate their rounded outer apertures.

In the ordinary JElasmohraiichii^ the branchial pouches are
more flattened from before backward, and their outer apertures
are more slit-like. The integumentary spaces between the
slits aie correspondingly narrower, and the adjacent w^alls of
successive pouches are more closely approximated, so that they
are di\dded only by septa ; but the vascular plaits of the sur-

THE TELEOSTEI. 141

face of the respiratory mucous membrane do not reacli the
outer edges of these septa.

In Chimcera, the free edges of the septa are exceedingly
narrow, and the apices of the branchial processes extend out-
ward to them.

In the Sturgeon, the septum is not more than three-fourths
as long as the branchial processes, the apices of which are
consequently free.

The process of reduction is carried still further in the Tele-
ostei — the septum not attaining to more than one-third the
length of the branchial processes ; and, as in the Ganoids,
each process is sui^ported by an osseous or cartilaginous
skeleton.

The Teleostei have no functional hj^oidean, or opercular,
gill ; and, as a general rule, each of their four branchial arches
possesses a double series of branchial processes, making eight
in all. Not unfrequently ( Cottus^ Cyclopteriis^ Zeus^ etc.), the
number is reduced to seven ; the fourth branchial arch having
only one series, the anterior. In this case, the gill-cleft, which
should lie between this arch and the fifth, is closed. Some-
times there are only six series of branchial processes, the fourth
arch being devoid of any (e. g., Lophius^ Diodoii). In Mai-
thcea the number is reduced to five, only the anterior series of
the third arch being developed ; and in Awphipnons cuchia
only the second branchial arch possesses branchial filaments,
the first, third, and fourth, being devoid of them.

Many Teleostean fishes possess accessory respiratory or-
gans. These may take the form of arborescent appendages to
the upper ends of some of the branchial arches, as in Clarias^
Heterohranchus^ and Seterotis / or, as in the Climbing Perch
(Anabas) and its allies, the epipharyngeal bones may enlarge
and acquire a labyrinthic honeycombed structure, and support
a large surface of vascular mucous membrane ; or, as in the Clu-
peoid {Lutodeira chcmos), an accessory gill may be developed
in a curved ceecal prolongation of the branchial cavity. Final-
ly, in Saccohranchus singio and in Arajyliipnous cuchia^ the
membrane lining the branchial chamber is prolonged into sacs,
which lie at the sides of the body, and receiv^e the blood from
the divisions of the cardiac aorta which supply the branchiae,
while they return it into the dorsal aorta.

All these fishes (except Lutodeira) are remarkable for their
power of sustaining life out of the water. Many inhabit the
marshes of hot countries, which become more or less desic-
cated in the dry season.

142

THE ANATOMY OF VERTEBRATED ANIMALS.

The kidneys of Teleostean fishes receive a great part of
their blood from the caudal vein, wliich ramifies in them. They
vary greatly in length, sometimes extending along the whole
under-sm^face of the vertebral column, from the head to the
termination of the abdomen. The ureters pass into a urinary
bladder which opens behind the rectum.

The brain in the Teleostei has sol-
id cerebral hemispheres, and, when
viewed from above, the thalamen-
cephalon is hidden by the approxima-
tion to the hemispheres of the large
and hollow optic lobes of the mesen-
cephalon, which has a pair of inferior
enlargements, lohi inferiores. There
is a peculiarity about the structure of
the optic lobes, which has given rise
to much diversity of interpretation of
the parts of the brain in osseous fish-
es. The posterior wall of these lobes,
where it passes into the cerebellum, or
in the region which nearly answers
to the valve of Vieussens in mammals,
is thrown forward into a deep fold
which lies above the crura cerebri,
and divides the iter a tertio ad quar-
tiim ventriGulum from the ventricle
?h\Trthropufnerves'Tite of the optic lobcs throughout almost

cerebral hemispheres; C, the the whole extent of the latter. ThlS
optic lobes ; A the cerebeUum. ^^^^ . ^ ^^^ ;, ^^^^ . ^ „ ^^ Q.^ttsche. On

each side of it the floor of the ventricle of the ojDtic lobes is
raised up into one or more eminences, which have the same
relation to the optic lobes as the corpora striata have to the
prosencephalic vesicle.

The optic nerves simply cross one another, and form no
chiasma. The cerebellum is usually large.

The cephalic part of the sympathetic nerve is present, as
in the higher Vertehrata.

Each of the nasal sacs usually opens externally by two
apertures. In some Gymnodonts a solid tentacle is said to
take the place of a nasal sac.

The eyes are abortive in the Blind-fish of the caves of Ken-
tucky [Amhhjopus sjjelmus). A fibrous band often passes
from the back of the orbit to the sclerotic, and represents the
cartilaginous pedicle of the Elasmobranchs. There is no nic-

FiG. 50 — Brain of the Pike, view-
ed from above : A, the olfactory

THE TELEOSTEI. 143

titating membrane, but immovable external eyelids may be
develojDed. The choroidal gland, mentioned above, surrounds
the optic nerve between the sclerotic and the choroid. Very
generally, 2, falciform process of the latter membrane traverses
the retina and vitreous humor to the crystalline lens. This
represents the pecten of higher Vertebrata. As in other fislies,
the lens is spheroidal, and the cornea flat. The sacculus of the
auditory organ contains large sohd otoliths, which are usually
two in number — the larger, anterior one, is termed Sagitta ^
the smaller, posterior, Asteriscus. There are always three
large semicircular canals.

The reproductive organs are eitlier solid glands which burst
into the abdominal cavity, whence their reproductive elements
are conveyed away by abdominal pores ; or, as is more usual,
they are hollow organs, and are continued backward into ducts
which open beside, or behind, the urinary aperture.

Some few Teleostei are ovoviviparous (e. g., Zoarces vi-
viparus), the eggs being retained in the interior of the ovary,
and hatched there. In the male SyngnatJms, and other Lo-
phohranchii^ integumentary folds of the abdomen grow down
and form a pouch, into which the eggs are received, and in
which they remain until they are hatched.

The young of osseous fishes are not known to undergo any
metamorphosis, nor are they provided witli external gills, nor
with spiracula.

Tlie classification of the Teleostei is not yet in a thoroughly
satisfactory state, and the following arrangement must be re-
garded as provisional :

1. The Physostomi. — Tliis group contains the Siluroiclei^
the Cyprinoidel^ the Cliaracini^ the Cypyi'inodontes^ the Sal-
inonidoe, the Scopelini^ the Esocini^ the Morinyri^ the Galax-
icB^ the Cli(p>eidce, the Heteropygii^ the Murcenoidei^ Sym-
'branchii^ and Gymnotmi. The air-bladder is almost always
present, and, when it exists, has an open pneumatic duct. The
skin is either naked, or provided with bony plates, or cycloid
scales ; the ventral fins, when present, are abdominal in po-
sition. The fin-rays (except in the pectoral and dorsal fins of
sundry Siluroidei) are all soft and jointed. The inferior pha-
ryngeal bones are always distinct.

In all other Teleostean fishes the air-bladder is either ab-
sent, or devoid of an open pneumatic duct. Hence they are
termed, collectively, Physoclisti by Haeckel.

2. The iVnacanthini, — The body has cycloid or ctenoid

144 THE ANATOMY OF VERTEBRATED ANIMALS.

scales, or is naked. The ventral fins, if present, are jugular in
position. The fin-rays are all articulated. The inferior pharyn-
geal bones are distinct. ( OpJiidini^ Gadoidei^ Pleuronectidoe.)
The PleuronectidcB are the most aberrant of all Teleostean
fishes, on account of the disturbance in the bilateral symmetry
of the body, skull, and fins, to which reference has already
been made (p. 30).

3. The Acanthopteri have generally ctenoid scales, thoracic
or j regular ventral fins, entire fin-rays in some of the fins, and
distinct inferior pharyngeal bones. The JPercoidei^ Cata-
phractl^ Sparoidei^ Sciceoioidei, Lahyrinthici^ Mugiloidei^ N^o-
tacanthini^ Scomheroidei, Squwnipennes^ Tcenioidei^ Gohioi-
dei^ jBlennioidei.) JPediculati^ Theuthyes^ and Fistulares, be-
long to this great group.

4. The Pharyngognathi is the name given by Miiller to a
somewhat artificial assemblage of fishes, the only common
characters of which are the anchylosis of the inferior pharyn-
geal bones and the closed pneumatic duct. They have either
cycioid or ctenoid scales. The ventral fins may be abdominal
or thoracic. The anterior dorsal and ventral fin-rays may be
either unjointed, as in the Labroidei^ Pomacentridcp^ Chro-
tnidce ; or articulated, as in the Scomheresoces.

The two remaining groups are very peculiar ; but I con-
fess I do not see upon what ground they can be regarded as
of ordinal value.

5. The Lopliobranchii. — The body is covered with bony
plates. The ventral fins are almost always absent. The infe-
rior pharyngeal bones are distinct. The branchial processes
have a clavate form, being larger at the free than at the at-
tached ends, and are in this respect unlike those of any other
fishes. [Fegasldce^ Sy7ignathidcf?.)

6. The Plectognatlii. — The body is covered with plates or
spines. The ventral fins are absent, or represented only by
spines. The inferior pharyngeal bones are distinct. The pre-
maxillas and, usually, the hyomandibular, are immovably united
with the skull — a character of rare occurrence among other
fishes. [GymnodoJitidce, Ostraciontidce^ JBalistidm.)

The greater number of Teleostei are marine. No Anacan-
thini, Plectognatlii^ or LophohrancMi^ and only one family of
Pharyngognathi (the Chro7nidoe), inhabit completely fresh
water. Comparatively few AcantliopAeri are fiuviatile. On
the other hand, by far the greater number of the Physostomi
are, either temporarily or permanently, fresh-water fish.

If the LepAolepidm [Thrissops^ Zeptolepis^ Tharsis) arr

THE DIPNOI.

145

Ganoids, the Teleostei are not known before the Cretaceous
epoch, when both Physostomi and Acanthopteri make their
appearance, under forms, some of which (e. g., Beryx) are
generically identical with fish living at the present day.

VI. The Dipnoi.— The " Mudfishes " of the rivers of the
east and west coasts of Africa and of eastern South America
are nearly transitional forms between the Pisces and the Am-
phibia.

The eel-like body, covered with overlapping cycloid scales,
tapers to a point at its caudal extremity, and is provided with
two pairs of long, ribbon-like, pointed extremities, and with a
caudal fin.

Fio. 51.— TLo Mudfish {Lepidosirm).

Mrz

Fm. 52. — Skull ot Lepidosiren annectens : A, the oarieto-frontal bone; J5, the supra-orbi-
tal ; C, the nasal ; D, the palato-pterygoid ; E, tne vomerme teetn ; E^ {?., the ex-occipi-
tal ; Mn, the mandible ; Hy, the hyoid ; Br\ the branchiostegal rays ; Op^ the opei-euJaJr
plate ; cc, the parasphenoid ; y, the pharyngo-branchial ; (?/•, the orbit ; Au^ the auditory
chamber ; ^, the nasal sac

7

146

THE ANATOMY OF YERTEBRATED ANIMALS.

The spinal column consists of a tliick notocliord, invested
by a cartilaginous sheath, without aiiy osseous or cartilagi-
nous vertebral centra. The proximal ends of ossified neural
arches, of ribs, and, in the caudal region, of inferior arches, are
imbedded in the sheath of the notochord.

Fin-rajs support the median fin. The skull, the palato-
quadrate, and suspensorial apparatus, form, as in CldinCBra^
one continuous cartilaginous mass, into the base of which the
notochord penetrates, terminating in a point behind the pitu-
itary fossa.

No cartilage bone is developed in the place of the basi-occi-
pital, supra-occipital basisphenoid, or presphenoid ; and there
are only two such ossifications, which represent the ex-occipitals
{E. 0.) in the side-walls of the cranium. A large parasphenoid
(x) underlies the base of the skull. Upon its roof a great single
bone (^), answering to the parietals and frontals, extends
from the occipital to the ethmoidal regions. In front of this
are two nasal bones ( C). There is no alisphenoid, but the
fronto-parietal and parasphenoid send processes toward one

B A ^t

Fjg. 53. — Longitudinal and vertical section of the skull of Lepidosiren. The cartilage is
dotted ; the membranous and bony constituents are shaded with lines. A^ B^ (7, 2), E^
Hy, as in the preceding figure ; a?, a?, the parasphenoid ; P, /S^, cartilaginous presphenoi-
dal region ; ch^ notochord ; Au, situation of auditory chamber ; 1, 2, first and second
vertebrae; //., F., VIIL, exits of optic, trigeminal, and vagus nerves; a, quadi-ato-
mandibular articulation.

another, which unite in front of the exit of the third division
of the fifth nerve. There is no interorbital septum, and the
cavity of the skull remains of tolerably even diameter through-
out. In front of the exit of the optic nerves, however, it is
longitudinally divided by a membranous septum.

The ethmovomerine cartilage is continued to the anterior
extremity of the skull. It bears teeth, but no distinct vomer.

A great palato-pterygoid osseous arch [D) extends from
the middle line along the upper and the under surface of the

THE DIPNOI. 147

palato-quadrate arch on each side to near the articuhir surface
of the mandible. In the middle of the roof of the mouth, di-
vergent, cutting, dentary plates are developed upon it. An
osseous nodule lies in the articular head of the palato-quadrate
cartilage, and is continuous with the bone F.

The mandible presents dentary plates corresponding with
those of the palate, and biting between the latter. The hj^oi-
dean arch is attached to the posterior and lower edge of the
suspensorium — which bears a bony ray representing an oper-
culum — while the hyoidean arch itself carries a single bran-
chiostegal ray (^r, Fig. 62).

The pectoral arch is composed of a median cartilaginous
part, with two lateral portions of cartilage, at once separated
from, and connected with, the median cartilage by bone. The
bone is separated from the cartilage by a layer of connective
tissue, and seems to represent the clavicle, while the cartilage
answers to the coalescent coraco-scapular cartilages of other
fishes.

The filiform fin is supported by a many-jointed cartilagi-
nous rod, articulated proximally with the coraco-scapular.
Upon this are disposed fine fin-rays like those of the Elasmo-
branchs, which support the marginal fringe of the fin. The
ventral fin has the same structure as the pectoral.

The intestine possesses a spiral valve, and the rectum
opens into a cloaca. The lungs have remarkably stiff walls,
and extend through the greater part of the body, beneath the
spine. The glottis, opening upon the ventral wall of the
gullet, places them in communication with the cavity of the
mouth, into which the nasal sacs open by posterior apertures,
which lie inside the upper lip and constitute true posterior
nares. The heart has a small, but distinct, left auricle, into
which the blood which has been aerated in the lungs is re-
turned. In addition to lungs, Lepidosiren possesses both in-
ternal and external gills, but the latter are rudimentary in the
adult.

The different species seem to differ in the manner in which
the primitive aortic arches are metamorphosed ; but it may be
said, generally, that the first has disappeared ; the second sup-
plies an internal branchia developed upon the hyoidean arch ;
the third gives off the anterior carotid artery, and supplies
neither internal nor external branchia ; the fourth supplies
only the first external branchia ; the fifth and sixth supply
both internal and external branchiae ; while the seventh is
connected only with an internal branchia. The pulmonary

148 THE ANATOMY OF VERTEBRATED ANIMALS.

artery seems originally to have been given off from an eighth
aortic arch.

It is a remarkable circumstance that, while the Dipnoi pre-
sent, in so many respects, a transition between the piscine and
the amphibian types of structure, the spinal column and the
limbs should be not only piscine, but more nearly related to
those of the most ancient Crossopterygian Ganoids than to
those of any other fishes.

CHAPTER r/.

THE CLASS AMPHIBIA.

The Ichthyopsida. — Class 11. — Amphibia.

The only clearly diagnostic characters of this class as com-
pared with Fishes are the following :

1. Amphibia have no fin-rays.

2. When limbs are present they contain the same skeletal
elements as those of the higher Vertehrata.

Certain other structm-al peculiarities are common to the
whole of the Amphibia, and are very characteristic of them
without being diagnostic. Thus :

1. The body is usually devoid of any exoskeleton, and
when scales, or scutes, are present in recent A^njyhibia, they
are concealed within the skin ( Ccecilia, Ejohippifer). In the
extinct Labyrinthodo7ita, the dermal armor is confined to the
ventral region of the body.

2. The vertebral centra are always represented by bone.

3. The sacrum rarely consists of more than one vertebra,
though there are individual exceptions to this rule, as in
3fenopom,a.

4. The suspensorial apparatus of the mandible is continu-
ous with the skull, which has two occipital condyles, and no
completely ossified basi-occipital.

5. There are no sternal ribs.

The Amphibia are divisible into the following groups :
A. A distinct and often long tail ; the vertebrsD amphicoelous or opia-
thoeoelous ; the proximal elements of the tax'sus not elongated.
A. Two or four Umbs ; no scutes or scales.

I. Saiirobatrachia or Urodela.

a. External branchiae or gill-clefts persistent, or disappcarinj;
only in advanced age ; no eyelids ; vertebrae amphicoelous ;
carpus and tarsus cartilaginous.

150 THE ANATOMY OF VERTEBRATED ANIMALS.

1. Proteidea.

h. No branchia3 or branchial clefts in the adult ; eyelids present ;
carpus and tarsus more or less ossified ; vertebrae commonly
opisthocoelous.

2. Scdamandridca.

B. Limbs absent, or all four present. Three large pectoral osseous
plates and an armor of small scutes on the ventral surface
of the body ; vertebras amphiccelous ; walls of the teeth more
or less folded.

n. "Labyrinthodonta,

B. Tail obsolete in the adult.

A. Limbs absent; numerous minute dermal scutes imbedded in
the integument of the serpentiform body.

III. Gymnophiona.

B. All four limbs present, and the proximal elements of the
tarsus much elongated ; the body short, and the integument
devoid of small scutes, though dermal osseous plates are
sometimes developed in it

lY. Batrachia or Anura.

The integument in most A7}2phiMa is soft and moist, as in
the Frog, where numerous glands open upon its surface. The
Gymnophiona are exceptional, among existing AinpTiibia^
in possessing small, rounded, flexible scales, like the cycloid
scales of fishes, imbedded within the wrinkled integument.

In certain Batrachia ( Ceratophrys dorsata^ EpMp)pifer
aiirantiacus)^ flat dermal bony plates are developed in the
dorsal integument, and become united with some of the sub-
jacent vertebrae. Many of the extinct Labyrinthodonta^ and
probably the whole of the members of that group, possessed
an exoskeleton w^hich appears to have been confined to the
ventral surface of the body. Under the anterior part of the
thorax there is a sort of plastron composed of one jnedian and
two lateral plates. The median plate is rhomboidal. The
lateral ones are somewhat triangular, and unite with the
anterolateral margins of the median plate by one side, sending
a process upward and backward from their outer angles.
The outer surfaces of all these plates exhibit a sculpture, which
radiates from the centre of the median plate and from the
outer angles of the lateral plates. These plates are in close
relation with the pectoral arch, and probably represent the
interclavicle and clavicles.

Minute bony plates cover the surface of the throat in a
small African Labyrinthodont, Mlcropholis. I have not met
with dermal ossicles in this position in other Labyrinthodonts,

THE AMPHIBIA. 151

But in Archegosaiirus, Pliolidog aster ^ TTrocordyliis^ Kerater-
peton^ Ophlderpeton, Ichthyerpeton^ the integument between
the thoracic plates and tlie pelvis presents regularly-disposed
rows of small elongated ossicles, which, for the most part,
converge from without, forward and inward, toward the mid-
dle line. No trace of these appears upon the tail, nor in
any part of the dorsal region of the body, nor on the limbs.

The endoskeleton of the A.inpTiibia is least complete in
Archegosaurus^ where the centra of the vertebrae are repre-
sented only by bony rings, the ribs and the neurdl arches
being well ossified. In other Labyrinthodonts of the same
(Carboniferous) epoch, however, such as Anthracosaurus, the
centra of the vertebrae are completely ossified biconcave disks,
very like the centra of the vertebrae of Ichthyosaurus.

In the existing JProteidea, and in the Gymnophiona^ the
vertebral centra are amphicoelous. In the Salamandrldea
they are opisthocoelous. In Pip)a and JBonibinator they are
also opisthocoelous, but in other Batrachia they are, for the
most part, procoelous, but vary in different regions, some
being biconvex and some biconcave.

The first vertebra, or atlas, presents two articular cups to
the condyles of the skull, but there is no specially modified
axis vertebra.

The transverse processes may be simple, but in the Laby-
rinthodonts, and in the existing Salamanders, they are divided
into two processes — an upper tubercular^ and a lower capitular^
process. When the transverse process is thus divided, the
proximal end of the rib is correspondingly split into a capitu-
lar and a tubercular process.

In the Gymnophiona^ the Saurohatrachia^ and the Laby-
rinthodonta^ the number of the vertebrae in the trunk is con-
siderable, and the members of the two latter groups have long
tails. But in the Batrachia^ the total number of vertebrae
does not exceed eleven, of which eight belong to the presacral
region, one to the sacrum, and two (modified vertebrae) to the
coccygeal region. The transverse processes of some of the
presacral vertebrae are usually very long, but there are no
separatel}'' ossified ribs. The transverse processes of the sacral
vertebra are very large and expanded, and its centrum has
usually a single concavity in front and a double convexity
behind.

The coccyx consists of a long, cylindroidal, basal bone
proceeding from the ossification of the sheath of the termina-
tion of the notochord, and corresponding with the urostyle of

152

THE ANATOMY OF VERTEBRATED ANIMALS.

the Teleostei y and of two neural arches, which lie over its
anterior end, and become anchylosed with it. The anterior
face of the coccyx usually presents two concave facets for
articulation with the posterior convexities of the sacrum.

The cavity of the cranium is not narrowed anteriorly by
the development of an interorbital septum in any Amphibian.
All existing Amphibia have ex-occipitals developed in the
walls of the cartilaginous cranium ; but it is not certain that
any such ossifications existed in Archegosaurus, though they
are present in other Labyrinthodonts.

No Amphibian possesses a complete basi-occipital, supra-
occipital, basisphenoid, alisphenoid, or presphenoid cartilage
bone. In existing Amphibia, a prootic ossification appears
to be verj'^ constant. The constant existence of distinct opis-
thotic and epiotic elements is doubtful.

The Frog's skull is characterized by the development of a
very singular cartilage-bone, called by Cuvier the " os en
ceinture^'* or girdle-bone. This is an ossification which invades
the whole circumference of the cranium in the presphenoidal
and ethmoidal regions, and eventually assumes somewhat the
form of a dice-box, with one-half of its cavity divided by a
longitudinal partition. The latter, corresponding with the
front part of the bone, extends into the prefrontal processes
in some frogs, protects the hinder ends of the olfactory sacs,
and is perforated by the nasal division of the fifth nerve. The
septum, therefore, answers to the ethmoid, the anterior half

Fig. 54. — The cartilaginous cranium of Rana eficulenta. A, from above; B, from below;

2/, the " OS en ceintm-e," or girdle-bone.

of the girdle-bone to the prefrontals, or part of them, and the
posterior half of the girdle-bone to the orbitosphenoids of

THE AMPHIBIAN SKULL.

153

other Vertehrata. Turbinal ossifications are developed in the
cartilage bounding the nasal capsules in some Ampliibia,

Pm

z qj-\

Pmx,

Fig. 55. — Skull of Rana esculenta. A. from above; B, from below ; C. from the left sido
cc, parasphenoid ; y, girdle-bone ; Z, the " teujporo-mastoid."

The membrane bones of the Amphibian skull are : 1. Front-
als and parietals, which, in the BatracJiia^ may be fused to-
gether into one bone. 2. Nasals are generally present. 3.
The vomers, always present, are two in number, one for each
side, in all Amphibia but Pipa^ Dactylethra^ and Pelobates,

4. A great parasphenoid covers the base of the skull from the
occipital to the ethmoidal region, as in TeUostei and Ganoidei,

5. A membrane bone (Z), called " temporo-mastoid " by Du-
ges, lies on the outer side of the suspensorium, extending from
the side-walls of the skull to the articular head for the lower
jaw. The relations of this bone in its upper part are similar
to those of the squamosal of the higher Vertehrata., in its lower
part to those of the bone F in Lepidodren., to the preopercu-
lum of fishes, and to the tympanic of the higher Vertehrata,

Two premaxillae are always developed. The maxillae are
usually present, and may be connected, as in most J3atrac7iia,
by quadrato-jugal ossifications with the outer side of the end
of the suspensorium, in which an ossification representing the

154 THE ANATOMY OF YERTEBHATED ANIMALS.

quadrate bone is often developed. But tlie quadrato-jugals
(and even the maxillge) may be represented simply by more or
less ligamentous fibrous tissue, as is the case in the Urodela,
Pterygoid bones are developed in all Ainxjliibici^ and distinct
palatine bones in most, but not all, of the J^atixichia, The
suspensorium, which is inclined downward and forward in the
lower Urodela, passes almost directly downward, or a little
backward, in the higher, and in the JBatrachia slopes greatly
backward ; and it undergoes the same modifications in direc-
tion, during the progress of any of the JBatracJiia from the
larval to the adult state.

In the mandible, the proximal end of Meckel's cartilage is
rarely, if ever, completely converted into a bony, articular ele-
ment, but the distal moiety is ossified in some JBatrachia,
The membrane-bones of the mandible are a dentary and a
splenial piece, with perhaps an angular element.

The hyoidean arch is, in most Ajnphibia, connected with
the suspensorial cartilage — sometimes quite close to its origin,
sometimes near its distal end, in the Urodela. Its cornua are
stout and well ossified in the JProteidea. In the JBatrachia
they are slender, and their proximal ends may be free. Dis-
tally, they are connected with a broad lamellar body, from the
posterior margin of w^hich two processes which embrace the
larynx are usually given off. In the perennibranchiate Pro-
teidea, the hyoidean arches are united by narrow median en-
toglossal and urohyal pieces, as in Fishes.

In the JBatrachia, the branchial arches disappear in the
adult ; but in the GymnopTdona and in the Urodela, more or
fewer of the larval branchial arches persist throughout life.

In the Proteidea there are three or four branchial arches,
each usually consisting of two cartilaginous, or ossified, pieces
on each side. In the Salamandridea, there are, primitively,
four branchial arches, but of these, portions of only the two
anterior remain in the adult. Four are developed in the
Ccecilia, and three of these are permanent.

Some peculiarities exhibited by the skulls of the Gymno-
phiona, and by the JLiahyrinthodonta, are worthy of especial
notice.

In the former, e. g., in Ichthyophis gliitinosa, the skull is
covered b}'' a complete bony roof, formed, mainly, by the ex-
occipitals, parietals, frontals, prefrontals, nasals, and ascending
processes of the premaxillaries. Between the ex-occipitals,
the parietal, and the frontal, above, the maxilla, in front, and
the quadrate, behind and below, lies a bone which appears to

THE LIMBS OF AMPBIBIA.

155

answer to the bone (z) of the Frog, and to its qiiadrato-jugal.
Between the nostril and the maxilla, the nasal bone and the
premaxi'la, there is a bone which seems to be an ossification
of the cartilaginous ala 7iasi. Another bone nearly encircles
the orbit, and, as a supra- and postorbital bone, has no ana-
logue among existing Amphihia. The palatine bones sur-
round the posterior and outer margins of the posterior nares,
and then extend back on the inner side of the maxilla, in a
manner unlike any thing observed among other existing Am-
phibia, But in the Ldbyrintliodonta^ both this disposition
of the palatine and the complete roofing over of the skull by-
bone are repeated, and there is a postorbital bone.

jS.ir.

Fig, 56. — Side and upper views of the skull of Trematosaurus. The sculpture of the cra-
nial bones is not represented in the lower half of the upper view of the skull, in order to
show the sutures more distinctly.

The Labyrinthodont skull is further characterized by the
development of distinct pointed epiotics, like those of fishes,
and of paired ossifications, which take the place of the supra-
occipital, as in many Qanoidei. In many Labj^rinthodonts
the articular element of the lower jaw is completely ossified.

Archegosaurus possessed branchial arches when young,

156 THE ANATOMY OF YERTEBRATED ANIMALS.

and there can be little doubt that the other Labyrinthodonta
resembled it in this respect.

The limbs and their arches are completely absent in the
Gymnopliiona^ and, apparently, in the extinct Ophiderpeton
of the Carboniferous formation. In all other Amphibia the
pectoral arch and limbs are present, and, in all but Siren, the
pelvic arch and limbs. The anterior and j^osterior limb-arches
consist of a continuous cartilage on each side, divided by an
articular surface into a smaller dorsal moiety, and a more ex-
panded ventral portion. The dorsal moieties are, respectively,
the scapula and the ilium. The ventral moieties are divided
by notches, or fontanelles, into two portions — an anterior, pre-
coracoidal, or pubic part, and a posterior, coracoidal, or ischial
part.

In the TIrodela the scapula ossifies, and its ossification may
be prolonged into the coracoid and precoracoid, but there is
never more than one osseous mass. The clavicle is not devel-
oped. In Siredon, the Derotremata^ and Scdamandridea, the
coracoids are received into grooves of the anterolateral edges
of a cartilaginous sternum.

The pectoral arch of the Labyrinthodonts seems to have
possessed representatives of clavicles in the lateral thoracic
shields. The structure of the rest of the arch is not clear, but
ossified coraco-scapular pieces seem to have existed.

In the Satrachia^ the coraco-scapular cartilages are some-
times, as in the common Frog, firmly united in the middle
line, and send forward a median process, which becomes ossi-
fied, and is the omosternvm (Fig. 57, o.st.^. Behind, the cora-
coids articulate with a well-developed sternum (5^.). Distinct
ossifications arising on either side of the glenoidal cavity rep-
resent the scapula (^c.) and the coracoid {cr?), and the upper
moiety of the scapula may be distinctly ossified as a supra-
scapula [s.sc). The coracoid is divided by a large membra-
nous space ov fontanelle into a proper coracoid (cr.), which lies
behind the fontanelle ; a persistently cartilaginous epicoracoid
{e.cr.), which bounds it internally ; and a precoracoid, which
limits it in front. Closely applied to the precoracoid is an
ossification in membrane, which represents the clavicle.

The pelvic arch is attached (except in Proteus) to the ex-
tremity of the sacral rib. An iliac ossification is always devel-
oped ; an ischial, in all but Proteus. The pubis does not ap-
pear to be regularly represented by a distinct ossification. In
the Patrachia the applied flat faces of the expanded ventral
divisions of the pelvic arch coalesce into a disk.

THE LliTBS OF AMPHIBIA.

157

In the genus Amphiwna^ the limbs have each either two
or three digits. In Siren, the anterior limbs, which alone
exist, are ttSee- or four-toed. In Proteus, the anterior limbs

icst

Fia. 57. — The sternum and pectoral arches of a Frog, seen from above. The left supra-
scapula is removed: sc, scapula; s.sc, supra-scapula; ^)..<!c., prescapular process ; cr.,
coracold ; e.cr., epicoracoid ; cr.f., coracoid fontanelle. The bar which bounds this in
front is the precoracoid, and bears the clavicle : o.st, omosternum ; st, sternum ; x.st^
xiphisternom.

are tridactyle, the posterior didactyle. 3Ienohranchus has
tetradactyle feet, while in the other tirodela the anterior limbs
are tetradactyle, the posterior pentadactyle. The Batracliia
have four digits, with or without a rudiment of another, in the
fore-limb, and five in the hind-limb. In the perennibranchiate
Tirodela, the cartilages of the carpus and tarsus, which, except
in Proteus, present little deviation from the typical number
and arrangement (Fig. 11, p. 32), remain unossified ; in the
other Urodela, and in the Patrachia, they are for the most
part ossified.

In the Patrachia, the posterior lunbs are much longer than
the anterior. The radius and the ulna in the fore-limb, and
the tibia and fibula in the hind-limb, are fused together into
one bone. The carpal bones no longer present the typical
arrangement ; and, in the tarsus, there are tvvo proximal,
greatly elongated, cylindrical bones, which take the place of a
calcaneum and an astragalus, while the distal series is reduced.

The limbs of the Labyrinthodonts were feeble in compari*

158 THE ANATOMY OF YERTEBRATED ANIMALS.

son with the size of the body. In the genera Archegosaurns^
JS^eraterpeton^ Urocordylus, Lepterpeton^ each foot possessed
five digits, and the carpus and tarsus were unossified.

The Amphibia usually possess teeth on the vomers, pre-
maxillas, maxillae, and dentary pieces of the mandible, but
rarely on the palatine and pterygoid bones. The premaxillary
and vomerine teeth are disposed in concentric semicircles, an
arrangement which is very characteristic of the group. In
the larvae of the J^atrachia^ and in Siren^ the iDremaxillse and
mandibles are ensheathed in horny beaks, as in the Chelonia
and Aves. In addition, Siren has teeth in the vomers, and
on the splenial piece of the mandible ; Menohranchus and
8iredon have pterygoid teeth. Many of the Labj^rinthodonts
possess palatine teeth. In some Gyynnophiona the mandible
has a double row of teeth, and there is an approximation to
this structure in the Labyrinthodonts.

The teeth usually become anchylosed with the adjacent
bones. In existing AmpKibia their structure is simple, but
in the Labyrinthodonts, the parietes of the teeth, at a certain
distance below the summit, become longitudinally folded, and
each fold may be again longitudinally plaited, so that the
transverse section of the tooth acquires a very complicated
structure, the pulp-cavity being subdivided into a great many
radiating and branching segments. The structure is similar
in principle to that exhibited by the teeth of many of the
Ganoidei. In many of the LabjTinthodonts, again, two of
the anterior mandibular teeth take on the form of lono;- tusks,
which are received into fossee, or foramina, of the upper jaw,
as in most existing Grocodilia. The tongue is fixed to the
floor of the mouth in TIrodela and GymnopTiiona^ and remains
undeveloped in the genera Pipa and Dactylethra^ which have
thence been termed Aglossa. In other J^atrachia, the tongue,
which is usually long, and fixed by its anterior end to the sym-
physis of the mandible, can be rapidly protruded and used as
an organ of prehension. No distinct salivary glands have
been observed in the Amphibia. Many male JSatrachia have
the mucous membrane of the floor of the mouth produced into
pouches which can be distended with air.

The simple alimentary canal is usually short, and much
longer in the larvae (which are vegetable-feeders) than in the
adults. A gall-bladder is always present.

The heart presents two auricles, a single ventricle and a

THE CIRCULATION OF THE FROG. 159

huTbus arteriosus. A venous sinus, the walls of which are
rhythmically contractile, receives the venous blood from the
body, and opens into the right auricle. In Proteus^ 3Ie7io'bran-
chus, and Siren, the septum of the auricles is less complete
than in the other Am2^hihia, The left auricle is much smaller
than the right, and a single pulmonary vein opens into it.
The interior of the ventricle is more like a sponge than a cham-
ber with well-defined parietes. The walls of the long bulbus
arteriosus contain striated muscular fibres, and are rhythmi-
cally contractile. Yalves are sometimes placed at each end
of it, and it may be imperfectly divided into two cavities by
an incomplete longitudinal partition. It terminates, upon
each side, in either three, or four, trunks, which ascend upon
the branchial arches. The most anterior of these trunks give
oflf the carotid arteries, the most posterior the pulmonary ar-
teries, and arteries to the integument ; the middle trunks form
the principal roots of the dorsal aorta.

In Proteus, where there are three branchial arches, the
bulb of the aorta splits into tw^o trunks ; each of these divides,
at first, into two branches, and then the posterior branch, on
each side, again subdivides into two others. Thus, three pairs
of aortic trunks are formed, w^iich ascend upon the branchial
arches. The two anterior pairs of aortic trunks pass directly
into the roots of tlie dorsal aorta, but each gives off a vessel
which enters one of the external gills, the blood from which is
brought by an efferent canal into a higher part of the same
aortic arch. The third aortic trunk, on each side, is inter-
rupted, its lower part becoming the branchial artery of a gill-
tuft. The blood is carried out of this branchia by a venous
trunk, which opens into the root of the dorsal aorta, and is, in
reality, merely the upper part of the third aortic trunk. The
facts may be expressed in another way, by saying that the
bases of the branchial artery and vein anastomose in the first
two gills, but not in the third.

The adult Axolotl [Siredon) has four pairs of aortic trunks
(Fig. 25, E, p. 83) ; the hindermost pair (vi.) gives off the
pulmonary arteries, the three next (v., iv., ui.) supply the ex-
ternal branchiae ; and the anterior trunk pas&es, above, into an
artery which divides into hyoidean and carotid branches.

In Salammidra there are four pairs of aortic trunks in the
adult, but the upper moiety of the first, on each side, is oblit-
erated, and remains as a mere ductus Potalli. The fourth
trunk gives off the pulmonary artery; some twigs for the
oesophagiis, and a few cardiac branches, next arise from it;

160 THE ANATOMY OF YERTEBRATED ANIMALS.

and it tliea unites with the second and third to form the root
of the dorsal aorta. The basal moiety of the first trunk en-
larges at its extremity, close to the angle of the mandible, into
a spongy organ, the carotid gland, from which the carotid ar-
tery, and that for the supply of the hyoidean and oral regions,
are given off.

In the adult Frog, the aortic bulb is separated by an in-
complete longitudinal septum into two passages ; and, at its
extremity, divides into two trunks, each of which is parti-
tioned internally into three passages. The middle, or systemic,
passage passes directly into a trunk, which unites with its fel-
low beneath the spinal column into the dorsal aorta. The an-
terior, or carotid, passage ends, as in Salamajidra, in a ca-
rotid gland and ductus JBotalli / carotid, hyoidean, and oral
branches being given ofi" from the former. The hindermost,
ox put mo-cutaneous, passage ends in the pulmonary and the
cutaneous arteries, the anastomoses of these with the roots of
the dorsal aorta being obliterated. The middle pair of aortic
trunks thus exclusively constitute the origins of the dorsal
aorta, and are the permanent aortic arches. The right aortic
arch is wider than the left, especially toward their junction ;
as the left gives off, just before this point, a large coeliaco-
mesenteric artery to the abdominal viscera. Each aortic arch
gives off the subclavian and vertebral arteries of its side.
Only venous blood passes into the pulmonary arteries of a
Frog ; while mixed blood enters the aortic arches, and is of a
brighter arterial hue at the end, than at the beginning, of the
systole. The blood in the carotid passages is always bright.
The mechanical arrangements by which this is brought about
have been beautifully analyzed by Briicke, who shows — first,
that the spongy interior of the ventricle contains, in its base,
a transversely-elongated cavity, into which the auricles open,
and which, by its right extremity, communicates with the ven-
tricular opening of the aortic bulb ; secondly, that the aortic
bulb is imperfectly divided by a longitudinal septum, the
upper left edge of which is attached, while its lower right
edge is free ; thirdly, that, of the two passages into which the
aortic bulb is thus divided, the one on the right side of the
septum ends in a chamber, in which the carotid and systemic
passages commence, while that on the left side similarly leads
to the entrance to the pulmo-cutaneous passages ; fourthly,
that the carotid gland, in which the carotid passage ends, pre-
sents a mechanical obstacle to the flow of the blood through
it ; fifthly, that there is a valvular fold open toward the hearty

THE RESPIRATORY ORGANS OF AMPHIBIA. 161

in eacli systemic passage, which also offers a certain amount
of mechanical resistance to the blood ; and, sixthly, that after
the blood has begun to flow through the bulb, it will gradualjy

Fig. 58.— The Axolotl {Siredon).

force the septum over to the left side, and so impede the flow
into the pulmo-cutaneous passage.

Thus, when the auricular systole takes place, the right
auricle sends its venous blood into that division of the ventric-
ular cavity which lies nearest the opening of the bulb ; and,
when the ventricle contracts, the blood first driven into the
bulb is wholly venous. This blood fills the passages on both
sides of the septum, but finds a very much greater resistance
to its exit on the right than on the left side. It therefore
flows, at first, exclusively into the left division, and makes its
way through the short pulmonary arteries into the lungs.
But, as the pulmonary vessels fill, the pressure on the two
sides of the septum becomes equalized, and the systemic pas-
sages, which offer the next least resistance, fill with blood,
which is now mixed, as it comes from the middle of the ven-
tricle. Next, the septum, being driven over to the left side,
prevents any more blood from going into the pulmo-cutane-
ous passage. At the end of the systole, the blood driven out
by the ventricle is almost wholly that of the left auricle ; and,
by this time, the resistance in the systemic is as great as that
in the carotid passages. Hence the latter fill, and send arteri-
alized blood to the head.

The organs of respiration of the Amphibia, in the adull

162 THE ANATOMY OF YERTEBRATED ANIMALS.

state, are either external branchiae, combined with lungs, as
in the perennibranchiate TTrodela j or lungs only, as in the
other JJrodela, the 3atracliia^ the GymnopJiiona^ and, prob-
ably, the majority of the Labyrhithodonta,

In the perennibranchiate JJrodela^ the branchial arches (or
some of them) are separated by open clefts (the number of
which varies from four to two), throughout life, and three,
branched, gills are continued by single stems into the integu-
ment, at the dorsal ends of the branchial arches. An opercular
fold of the integument, in front of the gill-clefts, attains a
considerable size in Siredon (Fig. 58), but does not cover the
gills. The branchial arches themselves bear no branchial fila-
ments. Other Urodela are devoid of external gills, but (as is
the case in Menopoma and Ampliimna) present one or two
small gill-clefts on each side of the neck, and are thence called
Derotremata. The rest of the Urodela, and all the JBatracMa
and Gymnophiona, are devoid of both external gills and gill-
clefts, in the adult state.

In all the Amphibia., a glottis, placed on

the ventral wall of the oesophagus, opens into a

short laryngo -tracheal chamber with which two

t^\~§^\ pulmonary sacs are connected, either directly,

or by the intermediation of bronchi (as in the

Aglossa), or by a trachea (as in the Gy^nno-

Kc.-i//, ii„i \i phio7ia). The walls of the pulmonary sacs

'are more or less sacculated. In most Arn-

^''•°^;^^3^ phihia the lungs are equal in size ; but in the

snake-like Gyrnnophiona, the right is much
smaller than the left. In Proteus, the pul-
monary blood is not all returned to the heart,
'"-S.rTv. some of it entering the veins of the trunk.
Aerial resf)iration is effected, in the Artipliibia.^
by pumping the air from the oral cavity into
Fig. 59.-The brain of the luno's. To this end the m.outh is kept

Ran a esculenta, ^ , ^ • -, ,,-,... ^

from, above, magni- shut, and ingrcss and egress to the air is given
S[Zen'?e'pLi^n:'% ^he nasal passages, which always open
or olfactory lobes, immediately behind the vomers, at the anterior
tory' nerves; Ha'., P^rt of the roof of the niouth. These passages
s^heres^^^l o ^S" being opcn, and the hyoidean apparatus de-
thaiamencephaion presscd, the air fills the cavity of the mouth.
gbnd, i?i^; l!Tp^ ^^^^ external nostrils are then shut, and, the
optic lobes ; G, cere- hyoidean apparatus beino- raised, the air is

bellum; S. rh, the z.*^ j ,■, -^ ^i .-, i i.-- • x ii i

fou r th ventricle ; torccd, tlirough the opcn glottis, into the lungs.
Mo meduiiii obiou- ^\ AmpMbia possess a urinary bladder,

THE RESPIRATOEY ORGANS OF AMPHIBIA. 163

wliicli opens into the cloaca, and does not receive the ureters.
The Iddnejs of the Amphibia appear, like those of fishes, to
be persistent AVolffian bodies.

In the brain of the Aniphihia the cerebellum is always
very small, and represented by a mere band; the cerebral
hemispheres are elongated, and contain ventricles. In Proteus
the mesence|)halon is very indistinctly marked. The optic
nerves form a chiasma.

As in fishes, the pneumogastric gives oif a lateral nerve,
which runs along the sides of the bod3\

Tlie eyes are very small, and covered by the integument,
in Proteus^ the GymnopMona^ and the genus Pipa. The
perennibranchiate and derotreme ITrodela have no eyelids ;
but most Patrachia have not only a well-developed upper
eyelid, but a nictitating membrane, moved by special muscles.

All Aynphihia possess a fenestra ovalis with a cartilagi-
nous, or osseous, columelliform stapes, the expanded proximal
end of which is fixed to the membrane of the fenestra. In
many Patrachia, if not in all, there is a fenestra rotunda,
though the presence of a distinct cochlea has not been ascer-
tained. The ITrodela, the Gymnophiona, and the Pelobatidea,
among the Patrachia, have no tympanic cavity, nor mem-
brane. In the other Patrachia there are tympanic cavities
communicating freely with the throat. Each is closed exter-
nally by a tympanic membrane, with which the outer extremity
of the stem of the stapes is connected. In the Aglossa., the
two tj'mpanio cavities communicate with the mouth by a single
Eustachian aperture ; and the outer end of the stapes expands
into a great cartilaginous plate coextensive with the tympanic
membrane.

The ducts of the reproductive organs of the Amphibia^
like those of the Ganoidei^ always communicate directly with
the urinary ducts : and, as in most Ganoidei and all Elasmo-
brancMi, the proximal end of the oviduct is open, and com-
municates with the peritoneal cavity. The male has no penis,
unless a papillary elevation of the wall of the cloaca may rep-
resent such an organ. The testes of the male Amphibia are
composed of tubules, and vasa efferentia convey the contents
of these away. In the Urodela, the vasa efferentia of each
testis enter the inner side of the corresponding kidnej^, and
traverse it, leaving its outer side to enter a genito-itrinary
duct, which lies on the outer side of the kidney, ends blindly
in front, and opens behind into the cloaca. The uriniferous
tubuli also pass directly from the outer margin of the kidneys

164 THE ANATOMY OF VERTEBEATED ANIMALS.

into the genito-urinary duct. In the J^atracliia there is like-
wise a genito-urinary duct, and the vasa efferentia run to the
inner edge of the kidney and enter it. In £ornhinator igneus
and Discoglossus 2^ictiis, the genito-urinary duct receives the
urinary products and the spermatozoa, in the same way as in
the TIrodela, But, in the Frogs and Toads, the urinary tubuli
are gathered together into a special small canal which opens
into the genito-urinary duct near its termination in the cloaca,
and the vasa efferentia pour their contents into this canal.
Under these circumstances, the part of the genito-urinary duct
which lies beyond the renal canal may become obliterated, as
in the Frogs ; or may persist, and play the part of a vesicula
seminalis, as in the Toads.

In the female Amphibia, the kidneys have, as in the male
Frogs and Toads, a renal canal which opens into the lower
part of the oviduct.

It would appear from these facts that the oviduct in the
female, and the genito-urinary ducts in the male, Amphibia
represent both the Wolflfian and the Mullerian ducts of the
higher Yertebrata.

In most Amphibia the ova are impregnated and hatched
outside the body, but internal impregnation and incubation
occur in some of the TIrodela. In Pipa the eggs are hatched
in pouches of the dorsal integument, while the male Alytes
carries them twisted in strings round his legs.

When hatched, the young are devoid of respiratory organs
and of limbs, and are provided with a long tail, by means
of which they swim about. Branchial clefts soon make their
appearance ; and ciliated external branchial plumes, like those
of the perennibranchiate TIrodela, are developed. A pair of
suckers are sometimes formed upon the under-surface of the
mandibular region, and the jaws acquire horny sheaths.

A broad opercular membrane is developed in front of the
branchial aperture, and, in the ISatrachia, extends over and
eventually covers the gills, a rounded aperture persisting for
a certain time only on the left side. The anterior pair of limbs
is developed before the posterior, but in the Frog they are not
so soon visible, being hidden by the opercular membrane.

The lungs make their appearance as diverticula of the
ventral wall of the oesophagus. The nasal sacs are at first
mere caecal involutions of the integument, but nasal passages
communicating with the mouth are soon formed, and lioii:
aerial and aquatic respiration are completely established.

THE DEVELOPMENT OF AMPHIBIA.

165

In the Satrachia, as development proceeds, tlie external
branchiae disappear, and are succeeded, functionally, by short
branchial filaments developed upon the whole length of each
of the branchial arches, of which there are four.

Fio. 60. — A. B., Tadpoles with external branchiae: 7i, nasal sacs; a, eye; o, ear; k 5, bran"

chi£e ; to, mouth ; «, horny jaws ; s, suckers ; <?, opercular fold.
C, a more advanced Frog's larva : y, the rudiment of the hind-limb ; k s, the single branchial

aperture. The figure has not been reversed, so that this aperture appears to he on the

right side instead, of the left.

Before the development of the lungs the heart has only
a single auricle ; afterward, the auricle becomes divided into
two. The aortic arches, at first, pass along the visceral and
branchial arches to the dorsal aorta, as in other vertebrate
embryos. When external gills are developed, each receives a
loop from the corresponding arch, much as in Proteus,

When the internal gills of the Patrachia appear, each
aortic arch which belongs to a branchial arch splits into two
trunks, — one which remains directly connected with the cardiac
aorta, and another which opens into the dorsal aorta. The
vessels of the branchial filaments constitute loops between
these afferent and efferent trunks, which always remain united
by anastomoses. When branchial respiration ceases, and the
branchial processes and their vessels disappear, the anasto-
moses dilate ; the direct communication between the afferent
and efferent trunks of the second pair of internal branchiae is
reestablished ; and they become the permanent arches of the

166 THE ANATOMY OF VERTEBRATED ANIMALS.

aorta. The anterior branchiag are replaced by tlie carotid
glands, and their afferent vessel is the carotid passage of the
adult. The afferent and efferent trunks of the third pair of
brancliice are converted into the stem of the cutaneous artery,
and the afferent trunk of the fourth pair of branchiae into that
of the pulmonary artery. The diagram (Fig. 25, p. 83) is
intended to make these changes, and the relations of the
various trunks to the embryonic aortic arches, intelligible.

The alimentary canal of the Tadpole is, at first, long, and
3oiled up into a close spire, like a watcli-sjDring, in the ab-
domen, but its length becomes relatively less as age advances.
At the same time, the diet changes from vegetable to animal
— the young tadpole being chiefly herbivorous, the adult,
insectivorous.

In the TIrodela the tail persists, and develops complete
vertebrae ; but, in the JBatrachia, the caudal part of the spinal
column disappears, for the most part, together with the rest
of the tail, and only the basal portion of the notochord be-
comes converted into the urostyle, which eventually anchyloses
with the two hindermost neural arches.

CHAPTER V.

XUE CLASSIFICATION AND THE OSTEOLOGY OF THE EEPTILIA.

The province Sauropsida is divisible into the two classes,
Reptilia and Aves.

All Reptilia, so far as tlieir organization is known to us,
are distinguished from Aves by the following characters :

1. The exoskeleton is composed of horny plates (scales),
or bony plates (scutes), never of feathers.

2. Tlie centra of the vertebrae may be amphicoelous, pro-
coelous, opisthocoelous, or may have nearly flat articular faces ;
but these faces are spheroidal or oval, and are never cylin
droidal, even in the cervical region.*

3. When reptiles possess a sacrum, the sacral vertebra3
have large expanded ribs, with the ends of which the ilia
articulate.

4. The sternum is rhomboidal ; and, when many ribs are
connected with it, the hindermost of these are attached to a
single, or double, median backward prolongation (except, per-
haps, in the Pterosaiiria). The sternum may be converted
into cartilage-bone, but (with the possible exception of the
Pterosauria) is never replaced by membrane-bone, and does
not ossify from two, or more, definite centres.

5. When an interclavicle exists, it remains distinct from
the clavicles.

6. The manus contains more than three digits (? Dino-
sauria), and the three radial digits, at fewest, have claws.

7. In all existing reptiles, the ilia are prolonged farther
behind the acetabulum, than in front of it ; and the inner wall
of the acetabulum is wholly, or almost completely, ossified.
The pubes are directed downward and forward, and, like the

* The articular faces of the vertebrse of some Pterosauria are very much
elongated transversely.

168 THE ANATOMY OF VERTEBRATED ANIMALS.

ischia, meet in a ventral symphysis. In the extinct Dino
sauria, the pelvis exhibits forms transitional between the rep-
tilian and the ornithic arrangement.

8. The digits of the pes are not fewer than three ; and the
metatarsal bones are not anchylosed together, or with the distal
tarsal bones.

9. In existing reptiles not fewer than two aortic arches (a
right and a left) persist. Two arterial trunks are given off
from the right ventricle, or the part of the single ventricle
which answers to it. The venous and arterial currents of the
blood are connected, either in the heart itself, or at the origins
of the aortic arches.

10. The blood is cold. There are usually two semilunar
valves at the origins of the aortic and pulmonary trunks.

11. The corpora higemina lie upon the upper surface of
the brain.

In Aves, on the contrary :

1. The exoskeleton consists of feathers. Ossifications of
the dermis are rare, and never take the form of scutes.

2. In all recent birds, the centra of the cervical vertebrae,
at least, have subcylindrical articular faces. If, as in some
birds, the faces of the centra of the other vertebrae are sphe-
roidal, they are opisthocoelous, which is the rarest arrange-
ment among reptiles.

3. The proper sacral vertebrae of birds — that is to say,
those between, or through, the arches of which the roots of the
sacral plexus pass — have no expanded ribs abutting on the
ilia.

4. The sternum has no costiferous median backward pro-
longation, all the ribs being attached to its sides. The carti-
laginous sternum is replaced, in the adult, by membrane-bone,
and ossifies from two, to five or more, centres.

5. When an intercla\dcle exists it is confluent with the
clavicles.

6. The manus does not contain more than three digits, and
not more than the two radial digits have claws.

7. The ilia are greatly prolonged in front of the acetab-
ulum, the inner wall of which is membranous. The pubes
and ischia are directed backward, more or less parallel with
one another, and the ischia never meet in a ventral symphysis.

8. The astragalus sends up a process on to the'front face of
the tibia, and early anchyloses with the latter bone. In this
character, Birds differ from all existing Reptiles. The foot

THE DIVISIONS OF THE REPTILIJL 16U

contains not more than four digits. The first metatarsal is,
almost always, free, shorter than the rest, and incomplete
above. The other three are anchylosed together, and with the
distal tarsal bone, to form a tarso-metatarsus.

Some of the extinct JDlnosauria closely resembled birds
in the form of the tibia and astragalus, the immovable union
of the two bones, and. the reduction of the number of the
digits.

9. Only one aortic arch, the right, is present. Only one
arterial trunk, the pulmonic, is given off from the right ven-
tricle. Tlie arterial and venous currents communicate only by
the capillaries.

10. The blood is hot. There are three semilunar valves at
the origins of the aortic and pulmonary trunks. In all exist-
ing birds the extremities of the chief pulmonary passages
terminate in air-sacs. There is a rudiment of this structure
in the Cham^eleons, and the extinct Pterodactyles verj'- prob-
ably possessed such sacs.

11. The corpora higemina are thrown down to the sides
and base of the brain.

The Reptilia. — This class is divisible, by well-defined char-
acters, into the following groups :

A. The dorsal vertebrae (which, like all the other vertebrse, are devoid of
transverse processes) are not movable upon one another, nor are the ribs
movable upon the vertebrae {Pleurospomlylia). Most of the dorsal vertebrae
and ribs are restrained from motion by the union of superficial bony plates,
into which they pass, to form a carapace.

Dermal bones, usually nine in number, one of which is median and sym-
metrical, and the others lateral and paired, are developed in the ventral walls
of the thorax and abdomen, forming di plastron.

I. — Chelonia.

B. The dorsal vertebrae (which have either complete, or rudimentary,
transverse processes) are movable upon one another, and the ribs upon
them. There is no plastron,

a. The dorsal vertebrae have transverse processes, which are either
entire, or only very imperfectly divided into terminal facets {M-pe-
tospondijlid).
a. The transverse processes are long ; the limbs well developed, with
the digits united by the integument into a paddle ; the sternum and
sternal ribs are absent or rudimentary.

II. — Plesiosauria.

h. The transverse processes are short, and sometimes rudimentary;
the limbs present or absent; when they are fully developed, the
digits are free, and there is a well-developed sternum with sternal
ribs.

8

170 TEE ANATOMY OF VERTEBRATED ANIMALS.

a. A pectoral arcli and urinary bladder.

III. — Lacert'dia.
h. No pectoral arch, and no urinary bladder.

IV. — Ophidia.

b. The dorsal vertebrae have double tubercles in the place of transverse
processes {^Perosjjondylia). The limbs are paddle-hke.

y. — IcJdIu/osaicria.

C. The anterior dorsal vertebrae have elongated and divided transverse
processes, the tubercular being longer than the canitular division
( Suchospondylia).
a. With only two vertebrae in the sacrum.

VI. — Crocodilia.

h. With more than two vertebrae in the sacrum.
a. The manus without a prolonged ulnar digit

1. The hind-limb saurian.

VII. — Dicynodontia.

2. The hind-limb ornithic.

VIII. — Oryiitlioscelida.
h. The manus having an extremely prolonged ulnar digit.

IX. — Pterosauria.

I sliall describe the exoskeletal, endoskeletal, and dental
systems of the chief groups of the Heptilia., under the several
heads here enumerated, and I shall then give an account of
these systems in Aves. But modifications in the myology,
neurology, splanchology, and development of the two classes
may be conveniently considered together, under those several
heads, in another chapter.

1. The Chelonia. — The Tortoises and Turtles are those
reptiles which most nearly approach the AiJiphibia, though
they depart very widely not merely from the amphibian, but
from the ordinary vertebrate type, in some respects.

A horny epidermic exoskeleton is absent in the soft Tor-
toises [Trio7iyx)^ the bodies of which are covered by a soft
integument ; but, in the other Chelonia^ the epidermis is modi-
fied into horny plates, which constitute the so-called " Tor-
toise-shell," and have in general a very definite arrangement.
Tlje dorsal surface of the body presents three series of central
I'lates, of which five are in the middle and four upon each side
(4, 5, 4). The margins of the dorsal shield are guarded by
tweritj'-four or twenty-five plates ; one on the middle line in
front, called nuclial ; one or two behind, pygcd j and eleven

THE CHELONIA. 171

on each side, 'marginal. The ventral shield sometimes pre-
sents an anterior median scale ; but, more usually, there are
six pairs, disposed symmetrically. It will be seen, presently,
that these epidermic plates by no means correspond with the
bony dermal ossifications. In addition to these principal
plates, smaller scale-like patches of horny epidermis are dc"
veloped on other parts of the body, and on the limbs.

The dermal ossifications may best be described in connec-
tion with the endoskeleton.

Tlie presacral vertebras are few in number. In the Green
Turtle ( Chelone midas) there are eight cervical, and ten dor-
sal, in front of the sacrum, which is composed of two vertebrae.
In all the cervical vertebrae the neurocentral sutures persist;
there are no transverse processes, or ribs, and the spines are
low or obsolete. The first vertebra, or atlas, is a ringlike
bone, composed of three pieces, one basal and twj superolat-
eral. The second is a true axis vertebra, the central part of
the centrum of the atlas ossifying apart, as an odontoid bone,
and attaching itself to the front face of the centrum of the sec-
ond vertebra.

The other cervical vertebrae are remarkable for the singu-
lar variety in the disposition of their articular cups and balls.

Fig. 61. — The Alligator Terrapene {Chelydra Serpentina).

Thus the third is opisthocoelous ; the fourth, biconvex ;
the fifth, procoelous ; the sixth, also procoelous, but the . pos-
terior face is nearly flat, and very broad ; in the seventh, both
the anterior and the posterior faces are very broad and flat-
tened, the posterior being the more convex. The eighth cer-
vical vertebra is procoelous, and differs from the rest by the
expansion of its neural sj)ine, and by the arching backward
of its postzygapophyses over the convex prezygapophyses of

172 THE ANATOMY OF VERTEBRATED ANIMALS.

fclie first dorsal vertebra, upon whicli tlie former play back-
ward and forward.

All tlie cervical vertebrae are very freely movable upon
one another, and confer great flexibility on the neck. In
strildng contrast with this arrangement, the ten following
vertebrte have flattened faces, firmly united by cartilage. If
any one of these vertebras, from the second to the ninth, be
examined, it will be found that the elongated centrum is only
loosely united with the neural arch, and that the summit of
the neural arch is continuous with a broad flat plate of bone,
which forms one of the eight median elements of the carapace,
or neural plates (Fig. 62, Y).

There are no transverse processes, but a rib is articulated
between the centrum and the neural arch. At a short dis-
tance from its attachment, this rib passes into a broad plate
of bone, which extends upward to unite suturally with the
neural plate ; and, in front and behind, becomes similarly con-
nected with preceding and succeeding costal plates. The rib
may be traced along the under-surface of the costal plate, be-
yond the outer margin of which it protrudes ; and its free ex-
tremity is received into a pit in an elongated prismatic dermal
ossification, which forms one of a series of marginal plates
(Fig. 62, 31).

The first dorsal vertebra differs from the others in many
respects. The anterior face of its centrum is concave, and
looks downward and forward, while its prezygapophyses are

C --^r^F

\

Fio. 63. — ^Transverse section of the skeleton of Clidone midas in the dorsal region : <?•,
centrum; V, oxpanded neural plate; C, costal plate; R, rib; M, marginal plate; P, lat
eral element of the plastron.

much prolonged, in order to articulate with the convex poste-
rior face of the centrum and prolonged postzygapophyses of
the last cervical vertebra. The spinous process of this verte-
bra does not pass into the bony nuchal plate of the carapace,
which lies above it (Fig. 63, Nii)^ and its rib does not expand
into a costal plate, but becomes connected with the costal
plate of the second dorsal vertebra. The neural arch of this

THE CARAPACE OF THE CHELONIA,

173

rertebra is shorter, from before backward, than its centrum ;
and the neural arch of the second dorsal vertebra extends for-
ward and overlaps the centrum of the first, for the space thus
left unoccupied. The rib of the second vertebra is also carried
forward, and articulates not only with its own centrum and
neural arch, but with the posterior edge of the centrum of the
first vertebra.

These arrangements are repeated by the other dorsal ver-
tebrae and ribs, up to the ninth inclusive ; but, in the tenth,
the neural arch occupies only the anterior half of the centrum
of its own vertebra, and the rib is very small, and has no cos-
tal plate.

The union of the neural and costal plates of the eight dor-

Fig. 63. — ^Dorsal -view of the carapace of Clielone, mirlas : JVu, nuchal plate ; If, marina)
plates; H, ribs; 1-8, neural plates; 0.1-C.8, costal plates ; Py, pygal plates.

sal vertebrae, from the second to the ninth inclusively, gives
rise to the principal part of the carapace, or dorsal moiety of
the bony shell of the Chelonian. The first and the tenth dor-
sal vertebrae contribute nothing to the carapace, their small
ribs merely becoming attached to the costal plates behind and
before them.

In front of the first neural plate, and joined with it by a
seiTated suture, lies a larg^e nuchal plate (Fig. 63, JSTu), which

174 THE ANATOMY OF YERTEBKATED ANIMALS.

forms the anterior median boundary of tlie carapace. This
nuchal plate sends down from its under-surface a median pro-
cess, which is joined by ligament with the expanded neural
spine of the eighth cervical vertebra. Behind the eighth neu-
ral plate, three other median pygal plates (Fig. 63, Py) suc-
ceed one anotlier. The anterior tw^o of these are united by
sutures with the eighth neural and costals, and with one an-
other ; but the third is connected externally only with the
marginal plates. All three are perfectly distinct from the sub-
jacent vertebra3.

The sides of the carapace are completed, between the
nuchal and pygal plates, by eleven marginal plates (Fig. G3,
31) on each side. Eight of these receive the ends of the ribs
of the second to the ninth dorsal vertebra?, in the way already
described.

There is no doubt that the nuchal, the pygal, and the mar-
ginal plates of the carapace are membrane-bones, developed
in the integument, quite independently of either the vertebr86
or the ribs. But it appears that the neural plates and the
costal plates exist, as expansions of the cartilages of the neu-
ral spines and ribs of the primitive vertebra?, before ossifica-
tion takes place. This being the case, the neural and costal
plates are vertebral and not dermal elements, however similar
they may seem to be to the nuchal, pygal, and marginal plates.
But this ultimate similarity of bones of totally distinct origin
is not more remarkable here than in the case of the skull,
where the parietal and frontal bones stand in the same rela-
tion to the supra-occipital bone as the nuchal and pygal plates
do to the neural plates of the carapace.

There are no sternal ribs, and no trace of a true sternum
has yet been discovered in the Clielonia. The plastron is
wholly composed of membrane-bones, w'hich are developed in
the integument, and lie, in part, in front of, and, in part, be-
hind, the umbilicus of the foetus. The latter, at least, there-
fore belong to the abdomen, and the plastron is a thoracico-
abdominal structure.

In the turtle the plastron consists of nine pieces — one me-
dian and anterior, four lateral and paired (Fig. 64). These
f)ieces may be named — the median, entoplastron ; the first
ateral, exAplastron ^ the second, hyoxtloatron ^ the third, hypo--
plastron y and the iouvih^ xip>hiplastr on. ^ The e92toplastro9i

* Believing tlie plastron to answer to tlie sternum of other Verfciraia,
anatomists have termed these elements of the plastron entosternnm^ epister-
num^ hyostemum^ Jiyposternum^ and xipMsternum.

THE PLASTRON OF THE CHELONIA .

115

and the two epi2:>lastra correspond with the median and lateral
thoracic plates of the Labyrinthodont Amphibia, and very
probably answer to the interclavicle and clavicles of other
Vertebrata.

FiQ. 64. — The plastron of the Green Turtle (Chelone midax): T.cl, interclavicle; cL clavi-
cles ; IIi/p., hyoijListron ; ///J-i?., hypoplustroa ; Xp.^ xiphiplastron.

The sacrum consists of two vertebra?. The expanded
sacral ribs are not anchylosed with the centra and arches of
their vertebrae.

The tail is flexible, and consists of procoelous vertebr.'e.

Fig. 65. — ^External view of a section of the auditory re^'on of the skull in a Turtle {Ofielant
midas)\f. o., fenestra ovalis;/'. r., fenestra rotunda; esc, a^c, pse, external, anterior,
and posterior semicircular canals.

176

THE ANATOMY OF ^'ERTEBRATED ANIMALS.

The anterior caudal vertebriB have no transverse processes,
but possess ribs which may not become anchjlosed with the
centra. Thus the tail and the neck are the onlv re2:ions of
the spinal column of a Chelonian which are flexible.

In the skulls of the Ghelonia all the bones, except the
mandible and the hjoidean arch, are immovably united to-
gei.her.

In the occipital segment of the adult, the supra-occipital
is united with the epiotic, but the ex-occipital usually remains
perfectly distinct from the opisthotic. The basisphenoid is
large and distinct. The alisphenoidal region remains unossi-
fied ; but the large parietals send down a prolongation on
each side, w^hich plays the part of an alisphenoid. Neither
the presphenoid nor the orbitosphenoids are represented by

P'lo. 66. — Long-itudinal sections of the skull of the Tm-tlo. The upper fi;^ire represents the
entire skull with the outline of the brain in situ ; the lower gives a larger view of tho
inner face of the bones of the p^terior moiety of the skull.

THE CHELONIAN KULL.

m

Pmx

bone, but there are large frontals. In the periotic capsule the
large prootic and the opisthotic (Cuvier's occijnUde externe)
remain distinct bones, but the epiotic unites with the supra-
occipital.

The naso-ethmoidal cartilage largely persists ; but it be-
comes covered above and at the sides by a large bone, which
meets with its fellow in the middle line, and occupies the po-
sition of the lachrymal, prefrontal, and nasal. The premaxillge
are small, and usually united together. There is a single
vomer, produced downward into a median internasal plate,
which expands below, and joins the palatine plate of the
palatine bone.

Above the posterior and upper part of the orbit lies a post-
frontalj and, behind this, a squamosal is placed at the sides of
the periotic capsule, and above the large quadrate bone. The
postfrontal and spuamosal occupy the
upper part of the temporal region of
the skull. Below these, a quadrato-
jugal and a jugal connect the quad-
rate bone with the large maxilla.

In some genera, as Chelone and
Chelydra, the skull possesses a sort
of false roof, formed by the expan-
sion of a median ridge, developed
from the parietal bones, into a broad
plate, which becomes suturally united
with the postfrontals and squamosals, p^ \ ^

The quadrate bone is firmly fixed
to the sides of the periotic region of
the skull, and ends below in a strong
condyle for the mandibles. The long
and broad pterygoid bones unite with
one another in the middle line, and ^jg\
are firmly fixed to the base of the
skull, as in Plesiosaiiria and Groco-
dllia. They unite only Avith the up-
per part of the quadrate bone, as in
the latter reptiles.

The palatines are firmly united Fig. 6T.— The left half of the lui

..-I.-, *■ , ., ii.T*^ 1 •,, dcrside of the skull of a Turtle:

With the pterygoids, behind, and with iv^i, posterior nares.
the vomer above and in front. They

are prolonged downward, and develop a short palatine plate,
which unites with the produced and expanded lower edge of
the vomer, to bound the posterior nares. (Fig- 67, Y^o^ i\r\)

[78 THE ANATOMY OF VERTEBRATED ANIMALS.

The dentary pieces of the two rami of the mandible are
represented by one bone, as in Birds.

The hyoideau apparatus consists of a broad plate of car-
tilage with two longer anterior, and two shorter posterior,
ossified cornua. The cornua have no direct connection with
the skull.

The pectoral and pelvic arches appear, at first sight, to
have a very anomalous position in the Chelonia, inasmuch as
they seem to be situated inside, and not outside, the skeleton
of the trunk. But since the plastron does not answer to the
sternum of other Vertehrata^ but to part of the dermal skele-
ton, the anomaly does not really exist on the ventral side.
And, as to the dorsal side, the pectoral and pelvic arches of
the foetal Chelonian are at first situated in front of, or behind,
and external to, the ribs, as in other Yertebtxita. It is only
as development advances, that the first costal plate extends
over the scapula, and the hinder costal plates over the ilium.

The pectoral arch is ossified in such a manner that the
scapula and precoracoid form one bone, while the coracoid re-
mains distinct. The free ends of the coracoid and precoracoid
are usually connected together by a fibro-cartilaginous band,
representing the epicoracoidal cartilage in JOacertilia. There
is no clavicle, unless the epiplastra and entoplastron represent
that bone.

The carpus of the Chelonia contains nine primary ossicles,
as in the tfrodela — three in the proximal row, one central,
and five distal — and these almost always remain distinct.

There are five digits, the numbers of the phalanges of
which present no constancy.

The pelvis contains the usual bones. The pubes (which
are very large) and the ischia meet . respectively in a long
symphysis ; and, sometimes, the foramina ohturatoria are
completed, internally, by the meeting of the bony pubes and
ischium of each side in the middle line.

The pelvis is not usually united with either the carapace
or the plastron, but in Ghelys^ Chelodina^ and some other
genera, the ilia unite by synchondrosis, or anchylosis, with the
last costal plate, and the pubis and ischium with the xiphister-
nal plates, so that the pelvis becomes firmly fixed between the
carapace and plastron.

The proximal row of the tarsal bones consists usually of
an astragalus^ formed by the union of the tibiale and inter me-
dium^ and of di.Jihulare or calcaneum. In Ghelydra there is a

THE DIVISIONS OF THE CHELONIA. 179

centrale. In Clielone^ Emys^ Testudo^ and Trionyx the centraU
is united with the astragalus y and in Emys^ the calcaneuyn
coalesces into the astragalus^ so that the proximal portion of
the tarsus consists of one bone. In the distal series the two
fibular tarsals are united into a cuboid bone. There are five
digits, and the fifth metatarsal has a peculiar form, as if bent
upon itself at right angles, in the middle of its length.

In the Testudinea there are only two phalanges in each
digit of the pes.

The Chelonia are divisible into the Testudinea, the Emy-
dea, the Trionychoidea, and the Euereta.

1. The Testudinea have the horny jaws naked and cutting,
or denticulated. The eyes are lateral, the tympanic mem-
brane is exposed, the short and thick limbs have the toes
(all of which have nails) bound together by the integument.
The horny plates of the carapace and plastron are well de-
veloped.

The Land Tortoises belong to this division. The carapace
is usually very convex, and sometimes (as in the genus Pyxis)
the anterior part of the plastron is movable, and can be shut
up like a lid. In Clnyxis, the hinder part of the carapace is
similarl}'- mobile.

2. The Emydea have, usually, horny cutting jaws, un-
covered by lips ; the tympanum exposed, and the limbs more
slender than in the Testudinea^ with five-clawed digits, which
are only united by a web. The horny plates of the carapace
and plastron are well developed.

These are the River and Marsh Tortoises. They are further
divisible into two groups, in the one of Avhich, the Terraioenes,
the pelvis is free, the neck bends in a vertical plane, and the
head is almost completely hidden by the carapace when re-
tracted {Emys^ Cistudo^ Chelydra). In Gistudo^Ginostenum,
and Staurotypus, the hinder part of the plastron is mobile.
In the other division, the Gkelodines^ the pelvis is fixed to the
carapace and plastron, the neck bends sideways, and the
head cannot be completely retracted under the carapace
( Ghelys^ GJielodina.)

3. In the TrionycJioidea (Mud or Soft Tortoises), the jaws
have an external cutaneous lip ; the nasal organ is prolonged
into a kind of snout, and the head is covered by a soft skin
without any visible tympanic membrane. The limbs are flat-
tened, somewhat finlike, and pentadactyle ; but only three
iigits have nails. The integument develops no horny plates,

180 TIIE ANATOMY OF VERTEBRATED ANIMALS.

but is quite soft. The costal plates are shorter than in other
Chelonia^ and the marginal ossicles are either rudimentary or
absent.

The genera Gymnopiis^ Cryptopiis^ and Cycloderma, con-
stitute this division ; they all inhabit the fresh waters of hot
latitudes.

The Euereta^ or Turtles, have an exposed, hooked, horny
beak, with a blunt snout. The tympanum is hidden by the
integument. The limbs, of which the anterior pair are much
the longer, are converted into paddles, the digits being much
flattened and elongated, and immovably united together by
the integument ; only one or two nails are developed. The
skin of the body is either rugose {Sjyhargis)^ or covered with
thick epidermic plates {^Chelo7ie.)

The two genera composing this grouj) inhabit the seas of
warm climates.

The Chelonia are first known to occur, with certainty, in
the Lias. The older forms are, in many respects, intermediate
between the Euereta and the TrionycJioidea, but present no
approximation to any other order of Heptilia.

II. The Plesiosaueia. — In some of the Flesiosauria, the
head, not more than one-twelfth or one-thirteenth of the length
of the body, is mounted upon a neck as long, in proportion, as
that of a Swan ; but in others, the head is large and massive,
and the neck much shorter. The hind-limbs are longer than
the fore-limbs, and there is a comparatively short tail. The
integument was certainly devoid of any scutes ; and was, prob-
abl}^ smooth and possessed no scales.

The cervical vertebrae may exceed forty in number, though
they are generally fewer ; and as none of the ribs appear to
have been connected with the sternum, or if such connection
existed it cannot now be traced, it becomes difficult to dis-
tinguish between cervical and dorsal vertebrae, and one is
obliged to have recourse to some method of separating the
two, differing from that already adopted. Now, in these
animals, the neurocentral suture persists for a considerable
period, if not throughout life ; and the surfaces for the articu-
lation of the cervical ribs, which are at first altogether below
the neurocentral sutures, gradually rise, in the posterior parts
of the neck, until they first are cut by, and then rise above,
the suture. It is very convenient, and harmonizes very well
witl some facts to be mentioned by-and-b}' in the structure of
the Crocodllia^ to take the last of the vertebrae in which the

THE PLESIOSAURIA. 181

costji,! articular surface is cut by the neurocentral suture, as
the last of the cervical series.

The two anterior cervical vertebrce, as thus defined, con-
stitute the atlas and axis, and are frequently anchylosed to-
gether. The center of the other cervical vertebrae have slightly
concave anterior and posterior surfaces ; well-developed neural
arches ; anterior and posterior oblique processes, or zyga»
pophyses, of the ordinary character ; and stout, but somewhat
short, spinous processes. The centrum presents, upon each
side, an oval rugose pit, sometimes more or less divided
i.ito two facets. This is the costal articular surface, which
has been already adverted to. Into it fits the thickened head
of a costal rib, which may have corresponding facets, but is
otherwise undivided. The rib is continued backward into a
short and straight body, and the angle, or the part at which
the neck and the body of the rib join, is produced forward, so
that the cervical ribs of the Plesiosauria have a strong general
resemblance to those of the GrocodUia. In the posterior part
of the neck and the anterior part of tlie dorsal region, the ribs
become somewhat longer, and lose their anterior processes,
gradually acquiring the rounded and curved form of ordinary
ribs. Their proximal ends remain simple, and the facets, with
which they articulate, become raised, and thrown outward, as
transverse processes, developed from the arches of the verte-
brae. (Fig. 68, C.)

In the anterior dorsal vertebrae, these transverse processes
rapidly acquire their full length; and they are continued un-
der this form, descending somewhat lower upon the arches of
the vertebrae toward the sacrum, to the end of the dorsal re-
gion. The neural spines acquire greater length, the zyga-
pophyses are well developed, and the articular surfaces of the
centra retain the form which they possessed in the cervical
region. There are usually between twenty and twenty-five
dorsal vertebrae. The sacral v^ertebrae are two, and resemble
the others, except that the sacral ribs are large and broad for
the attachment of the ilium. The caudal vertebrae, usually
between thirty and forty in number, become, as usual, reduced
to little more than centra at the end of the tail ; but, in the
fore part of the tail, they have well-developed spines and ar-
ticular processes, with ribs which become anchylosed to the
bodies of the vertebrae, only late in life. Well-developed
chevron-bones are attached between the ventral margins of
successive centra of the caudal vertebrfie.

As has been mentioned, there appear to be no sternal ribs,

182 THE ANATOMY OF VERTEBRATED ANIMALS.

A

_ ITa.

JPmx. I

2^c.

FTi.

•30

FTj.

Fia. 68. — ^Diagram showing' the structure of the most important parts of the skeleton of
Plesiosuurus. — A, the skull: JSTa, nasal aperture. — B, the left fore-limb: IT, humerus;
U, ulna ; E, radius ; r. i. u., radiale, interm.edium, and ulnare, in the proximal row of
carpal bones; 1, 2, 3. distal carpal bones; Mc, metacarpus; Ph. phalanges. — C, a dorsal
vertebra with ribs {R.\ and ventral ossifications ( V.o). — D, the left hind-limb : F, femur;
T. tibia; F, fibula; t. i.f., tibiale, intermedium, and fibulare, in the proximal row of tar-
sal bones ; 1, 2, 3, distal tarsal bones ; 3It metatarsus ; PA, phalanges. — E, the pectoral
arch : Sc, scapula ; Co, coracoid ; a, clavicles and interclavicle (?). — P, the pelvic arch :
/*6, pubis ; II, ilium ; Is, ischium.

but there is a well-developed system of ossifications of the
wall of the abdomen, arranged in transverse rows from before
backward ; each row consists of a median bone, slightly bent
upon itself, thick in the middle, and thin at each end — and of
six other bones, three on each side, which are elongated and

THE PLESIOSAURIA. 183

pointed at each end, and so disposed that their pointed ends
overlap one another. (Fig. 68, C.)

In some JPlesiosaicria, as abeady stated, the skull (Fig. 68,
A) is very small in proportion to the body, not having more
than a twelfth, or a thirteenth, of the length of the latter; but,
in other species, the skull is much larger. The snout is taper-
ing and depressed, and the nasal apertures are situated, not
at its extremities, but just in front of the orbits — the latter,
hke the supra-temjDoral fossse, being wide. The occipital con-
dyle is almost wholly developed from the stout basi-occipital.
The ex-occipitals give off elongated parotic processes, and the
basisphenoid is a thick bone, which ends in front in a long
rostrum.

There is a well-marked parietal foramen, and the parietals
send off comparatively short processes backward, which be-
come connected -with the large squamosals. The latter unite
with the postfrontals, which separate the orbits from the tem-
poral fossa, and the orbit is completed behind by the junction
of the postfrontal with the jugal. The jngal bone is continued
backward into a slender bar, which extends as far back as the
lower end of the quadrate, and probably contains a quadrato-
jugal, so that there is a distinct infra-temporal fossa. The
most obvious circumstance in which the skull of Plesioscmrus
differs from that of most Heptilia is in the great size of the
premaxillaries, which constitute a large proportion of the
snout.

The under-surface of the skull is rarely well exposed in
its anterior part ; posteriorly, it exhibits a broad and long
expansion, formed by the pterygoid bones, which unite in the
middle line, and send processes outward and backward to
the quadrate bone. On each side of the middle line of this
region of the skull, is seen an ovoidal fossa or depression.
The pterygoids are continued forward, and are united exter-
nally with transverse bones, and more anteriorly with flattened
palatine bones. When the fore-part of the under-surface of the
skull is exposed, two other fossae are visible, one on each side
of the middle line, bounded behind by the palatine bones, and
separated by what appear to be the vomers. I conceive that
these are the time posterior nares, and that the posterior aper-
tures are simply spaces left between the pterygoid bones and
the basis cranii.

At the sides of the base of the skull, specimens of Plesio-
saurus occasionally exhibit two styliform bones, which lie
parallel with the axis of the skull ; these may be parts of the

184 THE ANATOMY OF VERTEBRATED ANIMALS.

hyoidean apparatus. No trace of any sclerotic ring has been
found.

The teeth of the Plesiosauria are sharp-pointed, curved,
and the outer surfaces of their crowns striated. Each tooth
is lodged in a distinct alveolus, with which, as in the CrocO'
dilia, it does not become anchylosed.

The pectoral arch (Fig. Q'^, E) is 'one of the most remark-
able parts of the organization of the Pleslosauria. It consists,
in the first place, of two very large coracoids, the long axes
of which are parallel with one another, while their inner edges
meet, without overlapping, throughout the greater part of
their extent. In this respect they differ from any of the
Lacertllla^ wdiich are provided with well-developed limbs. In
these the long axes of the coracoids always cut one another
at a large angle, open posteriorly — a circumstance which
results from the manner in which the coracoids are received
into grooves in the anterolateral edges of the rhomboidal part
of the sternum. Hence it would appear that the Pleslosauria^
like the Chelonia, did not possess any thing corresponding to
this rhomboidal part of the sternum, but that the intercoracoid
part of the sternum was either absent, or reduced to a mere
band, as in some JBatrachia.

The scapulae are unlike the corresponding organs in any
other reptile. Tlie glenoidal end, stout and strong, is con
tinned horizontally forward and inward, as a bony prism, with
a somewhat concave inner edge, and flat inferior surface. The
outer surface, rising up at right angles to the ventral surface,
gives rise to a well-defined edge; at a short distance from the
glenoidal end, the part of the bone which bears this surface is
produced upward and backward, into a low recurved plate.
This part appears to represent the proper body of the scapula
in other Reptiles, while the horizontal prolongation answers
to that preglenoidal process of the scapula, which extends
forward and inward as a free bony bar in many Lacertilia —
for example. Iguana.

In well-preserved specimens, a broad hoop of substance
(Fig. 68, E, a), which seems to have been but imperfectly
ossified, extends across the middle line of the bod}^, from the
preglenoidal process of one scapula to that of the other, and is
continued backward in the middle line, to the junction of the
two coracoids. This corresponds very nearly in form and
position to the epicoracoidal ossifications of the Lacertilia^
combined with the clavicles and interclavicles ; but I have
never been able to detect any distinct clavicular, or intercla-

THE PLESIOSAURIA. 185

vicular, elements in any P/mos^z«rw5, though they appear to
have been well developed in JSfothosaurus.

The humerus is a stout bone — prismatic, and with a rounded
head at its proximal end, flattened and broad distally. (Fig.
68, B.) Its anterior margin is nearly straight, or even slightly
convex, while the posterior is concave. Distally, it presents
two facets, meeting at an angle, with which tiie broad and
short radius and ulna articulate. The ulna differs in shape
from the radius, being convex posteriorly, and concave in
front. The two bones are of equal length, and much shorter
than the humerus. There are six rounded carpal bones,*
arranged in two rows ; and to these succeed five digits, com-
posed of metacarpals and phalanges, which are elongated and
constricted in the middle. The middle digits have numerous
phalanges.

The pelvic arch has very large dimensions, in correspond-
ence with the size of the hind-limb, which is usually longer
than the fore-limb. (Fig. 68, F and D.) The ilium is a
vertically elongated bone, narrower below than above, where
it becomes connected with the sacral ribs. Inferiorly, it unites
with the pubis and with the ischium, to form the acetabulum.
The pubes are very broad quadrate bones, much larger than
the ischia, and they meet in a median symphysis. The ischia,
triangular and expanded, also unite in a ventral symphysis.
The femur resembles the humerus in its general form, although
both its sides are straighter, and the other bones of the hind-
limb are so like those of the fore-limb, as to need no special
description.

There can be little doubt that all the bones of the limbs
were, like those of the Cetacea^ enclosed within a common
sheath of integument, so as to form a paddle.

Such is the general organization of the skeleton of the
Plesiosauria, which are long extinct animals, entirely confined
to the Mesozoic Rocks, from the Trias to the Chalk, inclusive.
They may be divided into two groujDS, according as they are
Triassic, or Post-Triassic, in age.

The Post-Triassic group contains the genera Plesiosaicrus
and Pliosaurus^ the different species of which appear to differ
in little more than the proportions of the head to the trunk,
and the relative length and degree of excavation of the centra

* It may be a question wlietlier the fourth distal bone in the carpus and
tarsus (Fig. 68, B and D) belongs to carpus and tarsus, or to metacarpus and
metatarsus ; or whether it is formed by the confluence of elements belonging
to both regions.

186 THE ANATOMY OF YERTEBRATED ANIMALS.

of the vertebrse. In the species which have been named
Pliosaurus, the vertebrae are wide in proportion to their
length, and deeply excavated in front and behind. Fliosaurus
attained gigantic dimensions, paddles of some individuals
reaching a length of not less than six feet.

The Triassic genera, JSFothosaiirus^ jSimoscmriis, Pisto-
saurus (for a knowledge of the organization of which we are
chiefly indejDted to the labors of Hermann von Meyer), appear
to have diifered from Plesiosaurus principally in the following
respects :

The connection of the neural arches with the centra of the
vertebrge seems to have been looser. The supra-temporal
fossae in the skull appear to have been larger in proportion.
In these animals, the under-surface of the skull has the same
structure as in Plesioscmrus, but a^Dparently lacks the poste-
rior fossae ; while there is no doubt whatsoever that the true
posterior nares are situated far forward, in the position as-
signed to them in Plesiosauriis.

The pectoral arch of N^othosaiirus^ again, presents a very
interesting deviation from the Plesiosaurian type. The cora-
coids, indeed, are greatly expanded, and meet by their inner
edges, so that the rhomboid al part of the sternum seems to
have been wholly absent, and the scapulae have a horizontal
prolongation, not quite so long as in Plesioscmrus^ with an up-
standing proper scapular part of corresponding shape. But
then the ends of these preglenoidal processes are connected
together by, and indeed suturally united with, a stout, curved,
transverse bar of bone, consisting of three pieces, one small
and median, and two very large and lateral, all united firmly
together by sutures. There can be little doubt that the con-
stituents of this bony bar correspond with the interclavicles
and clavicles of Lacertilia and Ichthyosauria.

III. The Lacerttlta. — Some few Lacertilia^ like the Cha-
maeleons and the A-mphisbmna?, are covered by a soft integu-
ment ; but, in the majority, there is an epidermic exoskeleton
composed of horny plates, tubercles, or spines, or overlapping
scales. In some forms (e. g., Scincus, Cydodus) the dermis
beneath the horny scales is ossified, and the body has a com-
plete armor of bony scutes, corresponding in form with the
scales. The dermal ossifications of the head may coalesce
with the subjacent bones, but this union of dermal bones with
subjacent parts does not occur in other parts of the body.

The spinal column always contains a considerable number

THE LACERTILIA. 187

of vertebrae ; and, except in the Amphishcenm and some few
other Lizards, the tail is long. Those Lizards which possess
hind-limbs have a sacrum, into which not more than three
vertebrae, and rarely more than two, enter. The presacral
vertebrae are distinguishable, when sternal ribs are present, into
cervical and dorsal. All those vertebra? which lie in front of
the first sternal rib are cervical ; and if, as sometimes happens,
the last two or three dorsal vertebrae are devoid of ribs, they
become lumbar. Not more than nine vertebrae are met with
in the cervical region of existing Lacertilia., and this number
is rare. The number was greater in some extinct Lacertilia.

The atlas is composed of three pieces, one inferior and
two superolateral. The odontoid bone is closely united with
the second vertebra, and its anterior face may be cylindroidal.
A separate ossification is sometimes formed on the under-sur-
face of the spinal column at the junction of each pair of ver-
tebrae. Such a separate ossification, or siib-vertehral wedge-
bone^ is commonly developed beneath and between the odon-
toid bone and the body of the second vertebra.

The centra of the vertebrae are either procoelous, or amphi-
coelous ; the former being by far the more common condition
in existing Lacertilia, all of which, except the Geckos and
SpJienodon, have procoelous vertebrre. The cups and balls
are usually ellipsoidal, the long axis of the ellipsoid being
transverse. In the Geckos, the centra of the vertebrae are
conically excavated at each end ; and, except in the centre of
each vertebra, Avhere it is ossified, the notochord persists
throughout the spinal column.

The sacral vertebrae of existing Lacertilia are not anchy-
losed together, nor are their articular faces modified, the two
being connected by a free cup - and - ball articulation. The
movements of the two vertebrae, however, are restrained by
the strong ligaments which connect their neural spines and
arches, and by the fibro-cartilage which connects and covers
the free ends of their expanded ribs.

In the anterior part of tlie tail of the Lacertilia there are
usually well-developed subvertebral chevron bones, which are
commonly attached to the bodies of the several vertebrae, and
not in the intervals between adjacent vertebra. In many
Lacertilia {Lacertm, Igiiance, G-ecJws) the caudal vertebrae
have a very singular structure, the middle of each being trav-
ersed by a thin, unossified, transverse septum. The vertebra
naturally breaks with great readiness through the plane of the
septum, and when such Lizards are seized by the tail, that

188 THE ANATOMY OF YERTEBRATED ANIMALS

appendage is prettj certain to part at one of these weak
points.

The arches of the vertebrre of the Lacertilia are articulated
together by the ordinary oblique processes, or zygapophyses.
In the Iguance they are additionally connected by a process
of the front part of each arch {zygosph&ne)^ which fits into a
fossa on the posterior face of the preceding arch {zygantrum).
These Lacertilian vertebras thus nearly ajDproach the vertebrae
of the Ophidia,

The transverse processes of the vertebrae are very short,
and are, at most, divided into two indistinct facets, with which
corresponding facets on the proximal ends of the ribs articu-
late.

Ribs may be developed in all the cervical vertebrae except
the atlas, and they usually increase in length toward the dor-
sal region, where more or fewer of them become connected
with the sternum. The dorsal moiety of the primitive carti-
lage of the rib becomes ossified, and the primitive cartilage-
bone is finally replaced by membrane-bone. The ventral moi-
ety becomes converted only into cartilage-bone, and may pass
directly and without articulation, on the one hand into the
sternum, and on the other into the vertebral rib. Processes
are sometimes developed from the posterior margins of certain
of the ribs, which are termed p>'^^ocessus iincmati. The ster-
num, when fully formed, consists of a rhomboidal anterior por-
tion, from the posterior angle of which a single, or double,
backward prolongation is continued into the wall of the abdo-
men. Two or three pairs of the sternal ribs are connected
with the posterolateral edges of the rhomboid, while the rest
may be attached to the abdominal prolongations ; or, behind
these, they may be continued into one another, to form com-
plete hoops across the wall of the abdomen (Geckos, Chamae-
leons, Scincoids).

The Flying Lizard {Draco volans) is remarkable for the
elongation of many of its posterior ribs, which are continued
into, and support, the parachute-like expression of the integu-
ment by which it is enabled to perform its flights.

The skull of the Lacertilia resembles that of the Chelonia
in the development of an interorbital septum (except in the
Amphishcence)^ and in the absence of alisphenoids, or of any
complete ossification of the presphenoidal or orbito-sphenoidal
regions. The premaxillae and maxillae are firmly united with
one another and with the skull, and there are two vomers. An
unossified space, the^;a?7*e^«^ybra»?e;i, usually remains in the

THE LACERTILIA.

189

roof of the skull in tlie course of the sagittal suture, or between
tJie parietals and the frontals.

Fmx To

!>&

Fig. 69. — The skull of Cyclodus, entire and longitudinally bisected.

In the principal group of the LacertiUa^ a column-like
membrane-bone, called the columella (but which is not to be,
bj any means, confounded with the stapes^ to which the same
name is often applied in Reptiles), extends from the parietal
to the pterygoid on each side, in close contact with the mem-
branous or cartilaginous wall of the skull. Hence they have
been called "^zonocrama," or " column skulls." This colu-
mella (Fig. 69, Co) appears to correspond with a small inde-
pendent ossification, which is connected with the descending
process of the parietal and with the pterj^goid, in some Che
Ionia.

In the great majority of the Lacertilia (as in the Chelo7iia),
the side-walls of the skull, in the region of the ear, are pro-
duced into two broad and long parotic processes, into the com-
position of which the opisthotic, ex-occipital, and prootio
bones enter. Each quadrate bone is articulated with the outer

190 THE ANATOMY OF YERTEBKATED ANIMALS.

end of one of these processes (in which a small separate pifero-
tio ossification sometimes appears), and is usually movable.
The parietal bones do not unite suturallj with the occipital
segment of the skull, or with the prootic bones, but are con-
nected with them only by fibrous tissue. And as the presphe-
noidal region remains unossified, or incompletely ossified, it
follows that the fronto-parietal portion of the skull is, in most
Lizards, slightl}'- movable upon the occipito-sphenoidal part.

Each parietal bone is prolonged backward into a process
which articulates with the upper part of the parotic prolonga-
tion of the skull ; and to the outer side of the posterior ex-
tremity of the parietal process the squamosal is attached. The
squamosal may be continued forward to the post-frontal, which
is sometimes subdivided into two. The post-frontal may unite
below with the jugal, and thus bound the orbit. Only in
Spheyiodon^ among recent Lizards, is the jugal connected with
the distal end of the quadrate by bone. As a general rule, the
quadrato-jugal is represented only by a ligament.

In consequence of the structure which has been described,
the posterior region of the ordinary Lacertilian skull presents
a number of distinct fossae in the dry state. A supra-temporal
fossa lies between the parietal, the post-frontal, and the squa-
mosal, on the upper face of the skull ; ^ post-te)nporal^ between
the parietal, the occipital, and the parotic apophysis on the
posterior f^ice ; a lateral-temporal^ between the squamosal and
post-frontal above, the jugal and quadrate in front and behind,
and the c[uadrato-jugal ligament below.

The pa,latine and pterygoid bones are firmly connected both
with the facial bones, and with the floor of the skull. Thus
the basisphenoid gives off two haslpterygoid processes, the
outer ends of which articulate with the inner sides of the ptery-
goid. The posterior ends of the pterygoids are usually con-
nected with the inner surfaces of the distal ends of the quad-
rate bones. Their anterior ends are firmly united with the
palatines ; and, from the junction of the two, a transverse
bone (Fig. 70, Tr) usually passes, to unite the palatine and
pterygoid with the maxilla.

The anterior ends of the palatines unite with the maxillae
and the vomers ; but, in existing Lacertllla^ they do not meet
one another, or come into contact with the basisphenoid or
presphenoid in the middle line. The palatine ajDortures of the
nostrils are placed between the palatine bones, on the outer
side, and the vomer, on the inner. In only a few Lacert'dia
do the palatine bones send down processes which bend tow-

THE LACERTILIA.

191

Pmx

n

ard one another in the middle line, and so form a posterior
nasal passage, partially separated from the oral cavity.

The two rami of the lower jaw are
usually, though not invariably, firmly con-
nected at the symphysis — and each is
composed of five ossifications in addition
to the articidare,.

The hyoidean apparatus consists of an
elongated median rod, the anterior part isM,
of which supports the base of the tongue ;
and, usually, of two long cornua on each
side of this. The cephalic ends of the an- p\
terior cornua ma}'^ be perfectly free, and
lie upon the sides of the neck, as in Psain-
mosauTus / or they may be traceable to,
and be connected with, the stapes and pt
the parotic processes, as in Spheiiodon.

The limbs may be completely devel-
oped ; or only one pair (either the ante-
rior or the posterior) may be present ;
or they may be entirely absent. When
present, they may be mere styliform rudi-
ments, or may possess any number of ^o\
digits from two to five. Even when the
limbs are altogether absent, the pectoral

as.

arch remains, though the pelvic

arch I^G. 70. — Under-view of th#
skull of Cyclodus: aV-,
posterior nasal aperture.

seems to vanish. When the pectoral arch

is complete, it consists of a suprascapula,

scapula, coracoid (wdth precoracoid and epicoracoid elements),

and tw^o clavicles, united by an interclavicle, which lies in a

groove of the sternum. (Figs. 12 and 13, pp. 35 and 36.)

The coracoids articulate with grooves in the anterolateral
edges of the sternum, and usually more or less cross and over-
lap one another, in front.

In the genus Lied is, in which not a trace of a fore-limb is
discernible, there is a small sternum, consisting of a flat,
somewhat pentagonal, plate of cartilage, in which there is a
little coarsely-granular calcareous deposit; but this sternum
is connected with no ribs, nor, though it lies betw^een the
coracoids, does it articulate with them. Each coraco-scapular
arch is a continuous cartilage, narrow in the middle, but ex-
panded at its dorsal, and still more at its sternal end, where
the right overlaps the left, and both are connected by fibrous
tissue with the sternum. The narrow middle part of the cora-

1S2 THE ANATOMY OF YERTEBRATED ANIMALS.

coid is invested, and in part replaced, by a sheath of membrane-
bone, which exi3ands above and below, and represents both
scapula and coracoid, though it presents no trace either of
division, or of a glenoidal cavity. Beyond tlie extremities of
this central ossification the cartilage merely presents scattered
granular calcification. Along the front edge of each coraco-
scapular arch, and closely connected with its ossified part, is a
long curved clavicle, entirely cooiposed of membrane-bone,
and united with its fellow in the ventral median line, by liga-
mentous fibres. There is no interclavicle. The pectoral arch
in other snake-like Lizards, such as the Blind- Worm [Angnis)
and the Sheltopusik [JPseudojjUs), is in much the same con-
dition as in Xiialis.

"When the hind-limbs are well developed, there is a com-
plete pelvis. The ilia are movably articulated with the fibro-
cartilages which cover the ends of the sacral ribs. The pubes
and the ischia meet in median symphyses, and the anterior mar-
gin of the pubis usually, as in the Chelonia^ gives ofi" a strong
curved process. In many Lacertilia a partially-ossified or car-
tilaginous rod {os cloacce) is continued back from the sym-
physis of the ischia, and sup23orts the front wall of the cloaca.

In most Lacertilia the manus jDossesses five digits ; and,
v/hen this is the case, there are usually eight bones in the
carpus — one for each metacarpal on the distal side, one radial,
one ulnar, and one central. As a very general rule, the pollex
has two phalanges, tlie second digit three, the third four, the
fourth five, and the fifth three (2, 3, 4, 5, 3). The pes, also,
generally possesses five digits, which increase in length to the
fourth, the fifth being smaller than the rest, and divergent in
direction. Two large bones, very closely united, or complete-
ly fixed together, represent the calcaneum and the astragalus,
and are articulated, in a manner which allows of very little
motion, with the tibia and fibula. In the distal row there is
usually a large bone, representing the cuboid. The fifth
metatarsal * is bent, as in the Chelonia, and may articulate
with the calcaneum as well as with the cuboid. One or two
of the cuneiform bones may be present, or the inner ones may
be represented merely by fibrous membrane, or by cartilage ;
in which latter case the inner metatarsals aj^pear to articulate
directly with the astragalus in the skeleton. The number of
the phalanges is very generally the same as in the manus for
the four tibial toes, but one more for the fibular (2, 3, 4, 5, 4).

* The bone thus named may perhaps contain a tarsal clement, and repre
seut, not only the fifth metatarsal, but the corresponding distal tarsale.

THE LACERTILIA. 193

The LacertiUa all possess teeth, wliich may be confined
to the premaxillce, maxillce, and dentary piece of the man-
dibles ; or may, in addition, be developed on the palatine and
pterygoid bones. These teeth are simple in structure, and
their crowns have very various forms, being sometimes sharp
and conical [Bfonitor) ; or blade-like, with serrated edges
{Iguana) ; or with broad, crushing, and spheroidal crowns
( Qyelodus). As a general rule, the teeth become anchylosed
to the adjacent bone with age ; and in the upper and lower
jaws they thus become attached, either by their sides to the
parapet of the jaw, when the dentition is said to be^^^ei^ro-
dont / or by their bases to the summit of the parapet, when
the dentition is acrodont. The extinct Protorosauria are
said to be thecodont^ or to have the teeth lodged in alveoli.
New teeth are usually developed at the bases of the old ones.

The LacertUia are divisible into numerous groups, the leading distinctive
characters of which are exhibited in the following table :

I. — The pterygoid and quadrate bones united.
A. A columella and an interorbital septum in the skull.
Klonncrauia (Stannius).

a. Amphicoelous vertebrae {K, AmpMccelia).

a. Dentition acrodont or pleurodont.

1. Ascalabota.

2. RhyncJiocephala.

3. Homceosauria.^

b. Dentition thecodont (?).

4. Prolorosau7'ia.*

b. Procoelous vertebra3 (IC. proccelia).

a. Not more than nine cervical vertebrae.

a. The nasal bone, single.

5. Flatynota.

b. The nasal bones, two.

1. The integument of the head not

covered with epidermic plates.

6. Eunota.

2. The integument of the head covered

with epidermic plates.

7. Lacertina.

8. Chalcidea.

9. Scincoidea.

h. More than nuie cervical vertcbrge.

10. J)olichosau7'ia.'*

11. Mosasauria.
B No columella ; no interorbital septum.

12. Amphishcenoida.

II. — The pterygoid and quadrate bones disunited.

13. Ckamodeonida.

♦ The columella has not been observed in these groups.
9

194 THE ANATOMY OF VERTEBRATED ANIMALS.

1. The Ascaldbota. — The Geckos, which constitute this
group, are Lizards of small size, which inhabit the hotter parts
of both the Old and the New Worlds, and have always attract-
ed attention by their habit of running with exceeding swift-
ness along the walls and ceilings of rooms. They are enabled
to maintain their hold under these circumstances, in part by
the sharpness of their curved, and, in some cases, retractile
claws ; and, in part, by laminated expansions of the integu-
ment of the under-surfaces of their digits, which appear to act
in somewhat the same fashion as the sucker of the Hemora^
or Sucking-fish.

The most important and distinctive characters of these
Lizards are :

Their vertebrse are amphicoelous.

Neither the upper nor the lower temporal arcades are ossi-
fied, the post-frontal being connected with the squamosal, and
the maxilla with the quadrate, by ligament.

The jugal is rudimentary, and the squamosal very small.

There are no eyelids, but the integument becomes trans-
parent as it is continued over the eyes. The integument is
soft, or coriaceous, not scaly.

2. The ^hynchocephala. — This division contains only the
very remarkable genus Sphenodon (otherwise Satteria^ or
Hhynchocephalus), The vertebrae are biconcave. Some of
the ribs have recurrent " uncinate " processes, as in Birds and
Crocodiles. The sternal and vertebral ribs are connected by
an articulation, and there is a very peculiar system of abdomi-
nal ribs. The infra-temporal arcade is completely osseous in
this, but in no other recent, lizard. The quadrate bone is im-
movably fixed, not merely by anchylosis with the squamosal,
quadrato-jugal, and pterygoid, but by the ossification of the
strong membrane, which, in Lizards in general, extends be-
tween the quadrate, the pterygoid, and the skull, and bounds
the front walls of the tympanum. The dentary pieces of the
mandible are not suturally united. The premaxillae are not
anchylosed together, and, as in some other Lizards (e. g., TIrO'
mastix), have a beak-like form, the large premaxillary teeth
becoming completely fused, with the bony substance of tlie
premaxilljB. There is a longitudinal series of teeth upon the
])alatine bone running parallel with those on the maxilla, and
the mandibular teeth are received into the deep longitudinal
groove which lies between the maxillary and the palatine
teeth. By mutual attrition, the three series of teeth wear one

THE rR( TOROSAURIA. I95

another down to tlie bone in such a way, that the mandibular
teeth are ground to an edge, while the maxillary and palatine
teeth are w^orn upon their inner and outer faces respectively.
The extinct Lizards of the Triassic age, HhyncliosauTus and
Syperodapedon^ appear to have been very closely allied to
Sphenodon.

3. The Homoeosauria. — The remains of Lizards of small
size, and agreeing in the most important points of their osteol-
ogy with the ordinary Lacertilia^ but having amphicoelous ver-
tebrae, have been found in the older Mesozoic rocks, from the
Solenhofen slates to the Trias inclusively. They cannot be
identified with either the Rhynchocepliala., or the Ascalahota^
and may be provisionally grouped as Homoeosauria, The
genera Somoeosaurus^ Sap>hoeosaurus^ and Telerpeton^ belong
to this group.

4. The Protorosauria. — These are the oldest known Sau-
ropsida, their remains occurring in the Kupferschiefer of
Thuringia, wdiich is a part of the Permian formation, and in
rocks of corresponding age in this country ; but no more mod-
ern representatives of this group are known.

The Thuringian Lizard [Protorosaurus) does not appear to
liave attained a length of more than six or seven feet. The
neck is remarkably long, the cervical region being equal to the
dorsal in length, and it bears a skull of moderate size. The
tail is long and slender, and the limbs w^ell developed, as in
the existing Monitors. Notwithstanding the length of the
neck, it contained not more than nine, possibly not more than
seven, vertebrae, which, except the atlas, are remarkably stout
and strong. There are about eighteen or nineteen dorsal, two
(or not more than three) sacral, and more than thirty caudal
vertebrae. In all these vertebrae the neurocentral suture is
completely obliterated, and the centra are slightly concave at
each end. The side of each cervical vertebra, after the atlas,
presents, near its anterior edge, a small tubercle, with which
the head of a slender styliform rib articulates. The transverse
processes of the dorsal vertebrae are very short, antero-posteri-
orly flattened, plates, and the strong ribs are articulated with
them by undivided heads. The sternum has not been pre-
served. In the abdominal region of some specimens, numerous
short and filiform bones appear to represent, and correspond
with, the abdominal ribs of Plesiosauria and Crocodilia,

The spinous processes of the caudal vertebrae, up to nea/

196 THE ANATOMY OF VERTEBRATED ANIMALS.

the middle of the tail, have the ordinary structure ; but bej'ond
this point they bifurcate, so that each vertebra seems to have two
spinous processes, a peculiarity unknown in other Lacertilia.

The laro-e chevron-bones are articulated between the bod-
ies of the caudal vertebrae, as in the Crocodllia^ but also as in
some LacertlUa^ such as the Geckos. The skull is preserved
in one specimen only, and in that it is in such an imperfect
condition that the details of its structure cannot be made out.
The teeth, however, are nearly straight, conical, and sharply
pointed, and seem to have been implanted in distinct sockets,
though there may be some doubt upon this point.

The pectoral and pelvic arches are large and strong. The
fore-limbs are shorter than the hind-limbs, and each limb
bears five digits. The manus contains certainly eight, possi-
bly nine, carpal bones, five of which correspond with the meta-
carpals. The number of phalanges is exactly the same as in
most existing Lacertilia (2, 3, 4, 5, 3). In the pes, again, the
number of the phalanges is characteristically Lacertilian (2, 3j
4, 5, 4), and so is the form of the fifth metatarsal, but the two
proximal tarsal bones appear to have been less closely connect-
ed together than in existing Lacertilia^ and there were, at
fewest, three distal tarsal bones with w^hich the metatarsals
articulated, and by which they were completely separated
from the proximal tarsals. Among existing Lacertilia an ar-
rangement similar to this is met with only in the Ascalabota.

5-9. The great majority of existing Lacertilia belong to
the procoelous Kionocrania,, with not more than nine cervical
vertebrae, and they deviate but little in their osteology from
the general type of organization which has been described.

The skull in the Platynota^ or Monitors of the Old World,
with the American genus Heloderraa^ differs from that of any
other Lacertilia in the circumstance that the nasal bones are
represented by a single narrow ossification.

In the genus Lacerta the bones of the roof of the skull
become continued into dermal ossifications, which roof over
the supra-temporal fossas. In the Chalcidea and Scincoidea,
in which the body sometimes becomes elongated and snake-
like, and the limbs rudimentary, the supra- and infra-temporal
arcades are apt to be ligamentous, and the post-frontals and
squamosals small.

10. The Dolicliosauria. — A very singular Lacertilian found
in the Chalk, and resembling an eel in form and size, has been

THE MOSASAURIA. I97

described by Prof. Owen under the name of JDoliGhoscncrus.
It possesses an exceedingly elongated body, but is provided
with limbs and with a distinct sacrum, consisting of two ver-
tebrae. Its most remarkable peculiarity, however, lies in the
number of its cervical vertebrse, which were not fewer than
seventeen.

11. The 3fosasanria. — The cretaceous rocks of Europe
and America have yielded another remarkable long-bodied
marine Lacertilian, which attained a great size. This is the
genus Mosasaurus^ remains of which were first obtained from
the Chalk near Maestricht.

Eighty-seven vertebroe belonging to one individual of this
genus have been discovered, and when put together had a
length of thirteen and a half feet. But there were certainly
many more vertebras than these, as those of the end of the
tail are wanting, and there are gaps in the series of the rest.
The centres of all these vertebras are concave in front and
convex behind ; but the concavities and convexities are less
marked in the posterior, than in the anterior, vertebrae. The
atlas and axis are not well preserved in this series of vertebras,
but the nine following all have inferior spinous processes,
which become shorter in the posterior vertebras, and, in the
last two, are represented only by a pair of low elevations.
They have short transverse processes, each terminated by a
simple costal facet. It is probable that these are cervical
vertebras. In the dorsal vertebrae, of which there must have
been at fewest twenty-four, the transverse processes, which
are strong in the anterior, gradually diminish in size in the
posterior, vertebrae. There are no inferior processes. All the
vertebrae which have been mentioned hitherto have the circum-
ference of the centrum rounded, and are articulated to one
another by zygapophyses. But a series of eleven, which fol-
low them, have no zygapophyses, and the centra assume a
more or less triangular prismatic form. The transverse pro-
cesses of these are Ions:, thin, and bent a little downward and
backward. These seem to have been lumbar vertebrae. No
sacrum has been discovered, but there are numerous caudal
vertebrae with transverse processes, pentagonally prismatic
centres, and chevron-bones attached to the middle of the
under-surface of each. In the nine posterior of these caudal
vertebrae the bodies are cylindrical, the transverse processes
are obsolete, and the chevron-bones, anchylosed to the under-
sides of the centra, are long, inclined backward, and overlap

198 THE ANATOMY OF VERTEBKATED ANIMALS.

one another. And, in the hindermost caudals, the spinous
processes and the chevron-bones disappear.

There were strong" ribs, but nothing is knoAvn with cer-
tainty of the sternum, limb-arches, or other bones.

The very complete specimens of the skull that have been
discovered prove that its structure was very similar to that of
the Old World Monitors in the large size of the nasal aper-
tures, and the fusion of the nasals into a narrow bone. 13ut
sharp recurved teeth are anchylosed by their bases, not only
to the premaxillary, maxillarj^, and dentary bones, but also to
the pterygoid bones ; and these pterygoid bones are unlike
those of other Lacertilia^ not only in form, but because they
articulate together in the middle line for a considerable dis-
tance behind the posterior nasal aperture.

12. The Ampliishoenoida. — These lizards have completely
snake-like bodies ; one genus of the group ( Chirotes) has a
pair of small pectoral members, but the rest are apodal. The
integument of the body is not scaly, but its surface is divided
into small rectangular arose arranged in transverse rows. The
tail is exceedingly short, so that the v^ent is close to the end
of the body.

The numerous procoelous vertebrre have less elliptical
articular faces than those of the typical Lacertilia. There is
no sacrum, and all the precaudal vertebrae, except the one or
two of the most anterior, have ribs. The representatives of
the chevron-bones in the tail are firmly united with the centra
of the vertebrae. The vertebrae have no zygantrum nor zygo-
sphene. Ampliisboena has no sternum. Chirotes has a ster-
num, but it is not united with the ribs.

The skull, unlike that of Lacertilia in general, develops no
interorbital septum. In this respect, and in the complete
closure of its anterolateral walls by bone, it resembles the
Ophidian cranium. There is no columella. Post-frontals are
absent, and the squamosal is very small. The quadrate bone
is small, and inclined not only downward, but forward, in a
manner unknown in other Lacertilia. The two rami of the
mandible are firmly united by suture.

In A.mphisbmna the premaxillge bear two rows of teeth,
one behind the other, and one tootli lies upon the symphysis
of the premaxillai.

13. The Chawceleonida. — The Chamasleons are distin-
guished from the I^ionocrarda not only by the negative

THE CnAMJELEONIDA. I99

character of the absence of the columella, which they share
with the preceding group, but by a number of very important
positive features. Among these I may mention the soft and
tuberculated skin, with its changing hues ; the absence of any
tympanum ; the prehensile tail ; and the very peculiarly modi-
fied feet. The digits are arranged in bundles of two and three,
the manus having the poUex, the index, and the medius, syn-
dactylous and turned inward ; while, in the foot, it is the
hallux and index only which are thus united and turned in-
ward, the three other toes being similarly connected together
by integument as far as the ungual phalanges, and directed
outward. To these characters may be added the remarkable
tongue, capable of protrusion and retraction with almost light-
ning rapidity.

The vertebrae of the Chamoeleons are similar in their char-
acters to those of the procoelous K^ionocrania. The sacrum
is composed of only two vertebra. Only a few of the anterior
ribs are united with the sternum. A large number of the
posterior ribs, as we have already seen to be the case in the
Gecko, unite together in the mid-line, and form continuous
hoops across the ventral wall of the abdomen.

But it is in the structure of the cranium that the Chamce-
leonida depart most completely from the ordinary Lacertilian
type. The parietal bone is not movable upon the occipital,
the supra-occipital sending up a median ridge, which unites
with the base of a corresponding crest or process extending
backward for a considerable distance from the middle line of
the parietal bone. The summit of this sagittal crest is joined
by two curved prolongations of the squamosal, the three
giving the occipital region of the Chamreleon its remarkable
casque-like form. The frontal bone is comparatively small and
single, and the nasals are very narrow, and do not bound any
part of the anterior nasal ajDertures. These apertures, in fact,
are situated upon the sides of the fore-part of the skull, and are
separated from the nasal bones, in part, by a membrane which
stretches outward from the nasal bones ; and external to this
by a prolongation forward of the prefrontal bone, which unites
with the maxilla, and in some specimens of Chamaeleons is
prolonged forward into a great osseous horn, projecting from
the sides of the front part of the snout.

The orbit is closed behind by the ascending process of the
^jugal bone, but there is no quadrato-jugal. The quadrate
bone itself is not, as in most other LacertiUa^ movable upon
the sides of the skull, but is firmly anchylosed with the bones

200 THE ANATOMY OF YERTEBRATED ANIMALS.

which lie adjacent to its upper end. The pterygoid bones
are produced downward ; and, bj a very exceptional peculiar-
ity, do not articulate with the quadrate bones, but are con-
nected with them only by fibrous tissue. In the lower jaw,
the dentary piece takes up a very much larger proportion of
the ramus than is the case in other Lacertilia. The basal por-
tion of the hyoid is represented by a long median cylindrical
entoglossal bone, and its posterior cornua are much stronger
and longer than the anterior pair. In the pectoral arch the
scapula and coracoid are remarkably longer and narrower than
in other Lacertilia, There are no clavicles, and the inter-
clavicle is w^anting, the sternum being represented only by its
rhomboidal ossified cartilage. Again, in the pelvic arch, the
ilium is long and narrow, and its long axis is directed nearly
vertically to that of the trunk — in which respect the Chamfe-
leons differ very much from the ordinary Lacertilia. There is
no 08 cloacm.

The carpus and the tarsus have a very singular structure.
In the carpus there are two proximal bones, articulated with
the radius and the ulna respectively. A single spheroidal bone
is articulated with these, and with the five proximal constit-
uents of the digits. Besides these, there is an ossicle repre-
senting the pisiform. In the tarsus there are also four bones,
two articulated with the tibia and fibula respectively, a third
below and between them, and a fourth distal bone articulating
with the five proximal bones of the digits. In both manus
and pes the number of the phalanges, counting from the pre-
axial to the postaxial side, is 2, 3, 4, 4, 3.

IV. The Ophidia. — This order of Reptiles has been divided
as follows :

A. The palatine bones widely separated, and their long axes longitudi-

nal ; a transverse bone ; the pterygoids united with the quadrate
bones.

a. None of the maxillary teeth grooved or canaliculated.

1. Aghiphodontia.

b. Some of the posterior maxillary teeth grooved.

2. Opisihoghjphia.

c. Grooved anterior maxillary teeth succeeded by solid teeth.

5. ProteroglypMa.

d. Maxillary teeth few, canaliculated, and fanglike.

4. Soleyiogliiphia.

B. The palatine bones meet, or nearly meet, in the base of the skull, and

their long axes are transverse ; no transverse bone ; the pterygoids
are not connected with the quadrate bone.

5. Typhlopidce.

THE OPHIDIA.

201

All the Snakes possess a scaly epidermic investment, which
it usually shed in one piece, and reproduced at definite inter-
vals. As a general rule these scales are flat, and overlap one
another ; but sometimes, as in Acrochordiis^ they become
more tubercle-like, and do not overlap. In the Rattlesnakes
(Grotalus) the body is terminated by several loosely- conjoined
rings o£ horny matter, which consist of the modified epidermis
of the end of the tail.

The derm does not become ossified in the OpJiidia,

The number of the vertebra in the Snakes is always con-
isiderable, and in some cases becomes very great, amounting
to more than four hundred in some of the large Pythons. The
spinal column is divisible only into caudal and precaudal re-
gions, as there is no sacrum, nor any distinction between cer-
vical, dorsal, and lumbar vertebras. The atlas and the odon-
toid vertebra are similar to those of the Lizards, and the atlas
is the only precaudal vertebra which is devoid of ribs. The
centra have nearly hemispherical articular surfaces, and thus
differ from those of ordinary LacertiUa^ while the superadded
articular processes found only in certain Lizards attain a great
development in the Snakes. The zygapophyses are broad
and flattened, and the outer surfaces of the anterior pair are
commonly prolonged into a process. The anterior surface of

Tt.S.

FiQ. 71. — ^Anterior and posterior views of the dorsal vertebra of a Python : z. s., zygosphene ;
s. a., zygautrum ; jj. 3., prezzgapophyses ; pt. s., postgygapophyses ; t. p., transverse
processes.

the arch above the neural canal is produced into a strong
wedge-shaped zygosphene, which fits into a corresponding
zygantrum of the next preceding vertebra ; and, on the pos-
terior surface of the arch, there is a zygantrum for the zygo-
sphene of the next preceding vertebra. (Fig. 71.)

202 THE ANATOMY OF YERTEBRATED ANIMALS.

The transverse processes are short and tubercle-like, and
the heads of the ribs which articulate with them are simple.
Each rib usually gives off a short upward process at a little
distance from its head ; it is curved, usually hollow, and ter-
minates, inferiorly, in a cartilage which is always free, no
trace of a sternum existing. Strong descending processes are
given off from the undersides of many of the presacral verte-
brae. In the caudal region, elongated transverse processes
take the place of the ribs. Chevron-bones, like those of the
Lacertilia^ do not exist, but the caudal vertebrae possess bifur-
cated descending processes, which bear similar relations to
the caudal vessels.

The skull differs from the ordinary Lacertilian cranium in
the following points :

1. That vertical elevation and lateral compression of the
presphenoidal region, which give rise to the interorbital sep-
tum, are wanting ; the floor of the cranium being nearly flat,
and the vertical height of its cavity diminishing gradually in
front, so that it remains spacious between the eyes, and in the
frontal region generally. The periotic region is not produced
into parotic processes.

2. The boundary-walls of the front half of the cranial cav-
ity are as well ossified as those of its posterior moiety, and the
bones which constitute the brain-case are firmly united to-
gether.

3. On the other hand, the nasal segment is less complete-
ly ossified, and may be movable. The premaxillse are usually
represented by a single small bone, which very rarely bears
teeth. It is connected with the maxillae only by fibrous tissue.

4. The palatine bones never unite directly with the vomer,
or with the base of the skull, but they are usually connected
with the maxillae by transverse bones ; and, by the pterygoids,
with the mobile quadrate bones. Hence the connection of the
palato-maxillary apparatus with the other bones of the skull is
always less close in Ophidia than in Lacertilia^ and some-
times it is exceedingly lax.

5. The two rami of the mandible are united at the sym-
physis only by ligamentous fibres, which are often extremely
elastic.

6. The hyoidean apparatus is very rudimentary, consisting
only of a pair of cartilaginous filaments, which are united to-
gether in front, and lie parallel with one another beneath the
trachea. They have no connection with the skull.

These are the most apparent differences between the

THE OPHIDIA.

203

Ophidian and the Lacertilian skull. But there are others, of
a less obvious but more remarkable character, by which the
skulls of the Ophidian depart not only from that of the Liz-
ard, but from that of other Vertehrata. Thus the basi-sphe-
noid passes in front of the sella turcica^ into a great rostrum,
which extends forward to the ethmoidal region, and probably
results from a parasphenoidal ossification. In many adult

f s.on Ftf P^^^ ^ s^

Qu.

Pmx

Fr

vct\ W_Jl^^ so

Pmx -y-Q

f iG. 72.— The skull of a Python, viewed from the left side, and in longitudinal section : Ctn,

stapes ; Tl, tui-binal bone.

Opliidia two cartilaginous rods lie in grooves on the upper
face of this rostrum, and pass behind into the basisphenoid,
while in front they are continued into the cartilaginous ethmoi-
dal septum. These rods are the trabeculce, cranii of the foetus,
which do not become united in Snakes, as they do in all the
other abranchiate Vertehrata. The roof and side-walls of the
Ophidian skull are completed in front of the occipital segment,
by two pairs of bones, which appear to be parietals and front-
als. The " frontal " bones not only completely wall in the
sides of the frontal region, but extend inward below", and meet
in the middle line, above the basisphenoidal rostrum and the
persistent trabeculse. The " parietals " unite suturally with
the basisphenoid. These relations are not usual in true front-
als or parietals (though the latter unite with the basisphenoid
in Ghelonia.^ and the frontals unite in the middle line of the
floor of the skull in some Mammals) ; and as there are only

B04 THE ANATOMY OF VERTEBRATED ANIMALS.

two bones in the place of four in this region of the skull, it
becomes a matter for inquiry whether the two bones, on each
side, respectively represent orbitosphenoids + frontals, and
alisphenoids + parietals ; or whether they rejDresent over-
grown frontals and parietals only ; or whether, lastly, they are
the result of an excessive development of the orbitosphenoids
and alisphenoids, true frontals and parietals being absent.
According to Rathke's elaborate investigation into the devel-
opment of the skull in Coluber natrix^ the two bones on each
Bide are formed from single centres of ossification, which ap-
pear in i^atches of " cartilage," which are situated, at first, in
the superolateral regions of the skull, in the place normally
occupied by orbitosphenoids and alisphenoids, and that these
grow up and meet in the middle line. In this case the bones
in question are orbitosphenoids and alisphenoids, and Ophidia
have no true frontals or parietals ; but the existence of so
remarkable a deviation from the ordinary construction of the
vertebrate skull cannot be admitted until the development of
the Snake's skull has been carefully reexamined.

The Ophidia usually possess well-developed post-frontals,
and they have large membrane-bones in front of the orbit,
which lie upon the cartilaginous nasal chambers, and are or-
dinarily regarded as lachrymals. Large nasals lie upon the
upper surface of the nasal capsule between the lachrymals ;
and, forming the floor of the front part of the nasal chamber,
on each side, is a large concavo-convex bone {Tl^ Fig. 72),
which extends from the ethmoidal septum to the maxilla, pro-
tects the nasal gland, and is commonly termed a turbinal,
though, if it be a membrane-bone, it does not truly correspond
with the turbinals of the higher Yertehrata. The squamosals
are usually well developed. There is no jugal, or quadrato-
jugal.

Though the general conformation of the skull in the Oj^hid-
^a is that w^iich has now been described, it presents remark-
able modifications in different members of the order, especially
in the form and disposition of the bones of the jaws. In the
great majority of the Ophidia^ the elongated palatine bones
have their long axes longitudinal, lie on the outer sides of the
internal nasal apertures, and do not enter into the formation
of the posterior boundaries of those apertures. Each is con-
nected by a transverse bone with the maxilla, which lies at the
side of the oral cavity ; and the pterygoids diverge posteriorly
toward the quadrate bones, with which they are connected by
ligaments.

THE OPHIDIA.

205

^iitsc

But, in the remarkable group of the Typlilopidm^ the slen«
der palatine bones meet upon the base of the skull in the mid-
dle line, and are directed transversely, in such a manner as
to bound the posterior nasal apertures behind, as in the JBatra-
chia. There is no transverse bone. The pterygoids lie par-
allel with one another under the base of the skull, and are not
connected with the quadrate bones. The maxillse are short
j^lates of bone which are connected with the outer extremities
of the palatine bones, and are directed obliquely toward the
middle line of the oral cavity, into which their free edges,
armed with teeth, depend.

Again, the first-mentioned, or typical, form of Ophidian
skull exhibits two extreme modifications, between which lie
all intermediate gradations. At the one end of the scale are
the non-venomous Snakes, and especially Python and Tortrix
(which belong to the division Aglypliodoyitia) ; at the other
the poisonous Snakes, and especially Crotalus {^Solenoglypliia),

Thus, Python (Figs. 72 and 73) has well-marked premaxillae,
large maxillary bones, palatine bones
which are firmly united with the ptery-
goids, and transverse bones which bind
the maxillaries and palato-pterygoid
bars into one solid framework.

The maxillaries give attachment to
a long series of recurved teeth, which ^
are not very unequal in size. And Py-
thon (like Tortrix^ but unlike all other
Ophidla) possesses teeth in the premax-
illae.

The squamosal bones are very long,
and adhere to the skull, upon which
they are slightly movable, only by their
anterior ends ; and the quadrate bones
are borne upon the posterior ends of
the squamosals, and are thus, as it were,
thrust away from the walls of the skull, g^
The rami of the mandible are loosely
connected by an elastic symphysial liga-
ment. Thus, not only can these rami
be widely separated from one another,
but the squamosal and quadrate bones
constitute a kind of jointed lever, the

•strnifrhtpninrr of whioli ■n<=»rmU« of flip» ^^- T3.— Under- Wew of tb€

Btraignreumg oi wnicn permitt, ot tne left half of the skull and fa
separation of the mandibles from the <aaX\)Qiies, oi Python,

206

THE ANATOMY OF VERTEBRATED ANIMALS.

base of the skull. And all these arrangements, taken together,
allow of that immense distention of the throat which is requi-
site for the passage of the large and undivided prey of the
serpent.

In Tortrix, this mechanism does not exist, the short quad-
rate bone being directly articulated with the skull, while the
squamosal, like the post-frontal, is rudimentary. The maxillary
bones are also almost fixed to the skull.

In the Rattlesnakes ( Crotalus^ Fig. 74), the premaxillse
are very small and toothless. The maxillary bone has no
longer the form of an elongated bar, but is short, subcylindri-
cal, and hollow ; its cavity lodges the fossa formed by the in-
tegument in front of the eye, which is so conspicuous in these,
and sundry other, poisonous Snakes. The upper and inner
part of the maxilla articulates with a pulley-like surface fur-
nished to it by the lachrymal, so that the maxilla plays freely
backward and forward upon that bone. The lachrymal, again,
has a certain amount of motion upon the frontal. The upper
edge of the posterior wall of the maxilla is articulated by a
hinge-like joint with the anterior end of the transverse bone,
which has the form of an extremely elongated and flattened
bar connected posteriorly with the pterj^goid.

A^a La--

jT (J. 74.— A, the skull of Crotahts, viewed from the left side; B, a transverse secUoTi takrn
at the point B, in Fij^. A, showing' T, the persistent cartila^nous trabeculse. The niiix-
llla is supposed to be ti-anspareut, and the anterior half of the palatine bone is BOt>n
through it.

THE OPHIDIA. 207

The latter is long and stout, and, as usual, is united, be*
nind, with the distal end of the quadrate bone. In front of,
and internal to, its union with the transverse it is prolonged
forward, and becomes united, by a movable joint, with the
short palatine bone, which is flattened from side to side,
and lies on the outer side of the posterior nasal aperture. Its
anterior end is connected only by fibrous tissue with the base
of the skull. The inferior edge of the palatine bears a few
small teeth, and other sharp, recurved, solid teeth are attached
to the under-surface of the anterior moiety of the pterj^goid.

When the mouth is shut, the axis of the quadrate bone
is inclined downward and backward. The pterygoid, thrown
as far back as it can go, straightens the pterygo-palatine joint,
and causes the axes of the palatine and pterygoid bones to
coincide. The transverse, also carried back by the pterygoid,
similarly pulls the posterior part of the maxilla, and causes
its proper palatine face, to which the great channelled poison-
fano's are attached, to look backward. Hence these fano-s lie
along the roof of the mouth, concealed between folds of the
mucous membrane. But, when the animal opens its mouth
for the purpose of striking its prey, the digastric muscle, pull-
ing up the angle of the mandible, at the same time thrusts
the distal end of the quadrate bone forward. This necessitates
the pushing forward of the pterygoid, the result of which is
twofold : firstly, the bending of the pterj^go-palatine joint ;
secondly, the partial rotation of the maxillary upon its lachrj;-
mal joint, the hinder edge of the maxillary being thrust down-
ward and forward. In virtue of this rotation of the maxillary,
through about a quarter of a circle, the dentigerous face of the
maxilla looks downward, and even a little forward, instead of
backward, and the fangs are erected into a vertical position.
The snake " strikes : " by the simultaneous contraction of the
crotaphite muscle, part of which extends over the poisou-
gland, the poison is injected into the wound through the canal
of the fang ; and, this being withdrawn, the mouth is shut, all
the previous movements are reversed, and the parts return to
their first position.

No Ophidian possesses any trace of anterior extremities,
but the Typhlopidoe^ the Pythons, Boas, and Tortrices^ have
rudiments of a pelvis, and the latter Snakes even possess very
short representatives of hind-limbs terminated by claws.

The teeth of the OpTiidia are short and conical, and be-
come anchylosed to the bones by which they are supported.

208 THE ANATOMY OF YERTEBEATED ANIMALS.

They may be developed in the premaxillaries, maxillaries,
palatines, pterygoids, and the dentary piece of the mandible,
but their presence in the premaxillaries is exceptional. In
JTtopeltis and some other genera, there are no palatine teeth ;
and in the egg-eating African snake, Hachiodon^ the teeth
are small and rudimentary upon all the bones which usually
bear them. But the inferior spines of eight or nine of the
anterior vertebrse are long, and tipped, at their apices, with a
dense enamel-like substance. These project through the
dorsal wall of the oesophagus into its cavity, and the eggs,
which are swallowed whole, are thus broken in a position in
which all their contents must necessarily be saved.

In the majority of the non-venomous Snakes the teeth are
simply conical, but in the others, and in all the poisonous
Snakes, some of the maxillary teeth (which are usually longer
than the rest) become grooved in front. In the Solenoglyphia^
or Vipers and Rattlesnakes, the maxillary teeth are reduced
to two or three long fangs, the groove in the front of which
is converted into a canal open at each end, by the meeting of
its edges. The teeth of the Snakes are replaced by others
which are developed close to the bases of the old ones.

Ophidia are not known in the fossil state before the older
tertiaries.

V. The IcHTHYOSATJRiA. — In its general form Ichthyo-
saurus presents a good deal of resemblance to a Cetacean.
The head is enormous, and passes at once into the trunk, so
that there is no more appearance of a neck than in a Porpoise,
and the body tapers off behind, much as would happen in the
latter animal were it devoid of a caudal fin. Indeed, there is
some reason to suspect that the tail of Ichthyosaurus may
have been provided with a sort of fin-like expansion of the
integument. This fish-like body was propelled, like that of
the Hesiosaurus^ by four paddles ; but the anterior paddles
were placed close behind the head, and were, generally, very
much larger than the posterior ones.

Pig. 75.— a restoration oi IchihyoBamnia. The existence of the caudal fin is doubtftil

THE ICHTHYOSAURIA.

209

The spinal column is only distinguished into two regions,
caudal and precaudal, inasmuch as the ribs, beginning at the
anterior part of the neck, are continued, without being con-
nected with the sternum, to the posterior end of the body ;
and there is no sacrum. The caudal region, however, is dis

Fig. 76. — Different parts of the skeleton of IchtJiyosanrvs inter'medivs, drawn to the sam'j
scale. A, the skull; B, the fore-limb: H^ humerus; E^ radius; U^ ulna; r. i. u., radi-
ale, intermedium, ulnare; Cp, carpalia; 1,2, 3, 4, 5, di^ts ; m.i'. m.u. radial and ulnar
marginal ossicles. — C, a doi-sal vertebra, -with the ribs (i?) and ventral ossifications
{V.O).—Y>. the hind-limb: F, femiir; T, tibia; Fh, fibula; t, i,f, tibiale. Intermedium,
fibulare; Ts, tarsalia; Mt, metatarsalia ; P/i, phalanges; m, tb, tibial marginal ossicles
— E, the pectoral arch, seen from the ventral side ; F, the same aspect of the pelvic axch

210 THE ANATOilY OF YERTEBRATED ANIMALS.

tinguished by the chevron-bones which are attached beneath
its vertebrse. The vertebrae of Ichthyosauria in general have
certain characters by which the}^ differ from those of all other
Vertebrata. (Fig. 76, C.) Not only are the centra flattened
disks, very much broader and higher than they are long, and
deeply biconcave (circumstances in w^hich they resemble the
vertebrge of some Labyrinthodonts and Fishes), but the only
transverse processes they possess are tubercules, developed
from the sides of these centra; and the neural arches are
connected with two flat surfaces, one on each side of the
middle line of the upper surface of the vertebrge, by mere
synchondroses. The neural arches themselves are forked
bones, with only rudiments of zygapophyses, and in the
greater part of the body do not become articulated with one
another at all.

In the cervical region, if one ma}" call " neck " the most
anterior part of the vertebral column, the front j^art of the
lateral surface of each vertebra presents two separate eleva-
tions, or articular surfaces, which are at first situated in the
upper half of the lateral surface. Toward the posterior half
of the dorsal region they descend, and, gradually approaching
one another, coalesce into one in the caudal vertebrae. The
form of the proximal ends of the ribs corresponds with the
arrangement of these tubercles ; for, where they are separate,
the proximal end of the rib is forked. The lower fork, or
capitulum, goes to the capitular, or lower, tubercle, and the
upper branch, or tuberculum, to the upper, or tubercular,
elevation. In the caudal region, where the articular surface
is single, the proximal end of the rib is also undivided. In
the caudal region the ribs are short and straight, but in the
precaudal region they are stout and curved, and much longer
in the middle than at either end of the series. The atlas and
axis resemble the other vertebrae in their general form: but a
wedge-shaped bone is, as it were, let in between their opposed
lower edges ; and a similar bone, attached to the under-part
of the concave face of the centrum of the atlas, serves to com-
plete the cup for the occipital condyle.

The skull of Ichthyosaurus (Fig. 7G, A) is remarkable for
the great elongation and tapering form of the snout, the huge
orbits, the great supra-temporal fossse, and the closing over of
the infra-temporal fossa3 by plates of bone. Again, the two
rami of the mandible are united in a symphysis, w^hich, for
length, is comparable to that observed in the modern Gavials
and in the ancient Teleosauria. The basi-occipital bone fur-

THE ICHTHYOSAURI A. 211

nislies the round articular condyle to the first vertebra, and
becomes very stout and thick in front. It appears to have
been anchylosed neither with the basisphenoid nor with the
basi-occipital. The latter bones are adapted to its sides, and,
together with the supra-occipital, which is interposed between
them above, circumscribe the occipital foramen. The basi-
sphenoid, a deep and stout bone, is produced in front into a
iong and slender parasphenoidal rostrum. There do not ap-
pear to have been any ossified alisphenoids. The parietals re-
main separate throughout life ; and, in some species, not
merely present a great parietal foramen close to the coronal
suture, but are completely divided by a median fissure. Ossi-
fied presphenoids and orbitosphenoids appear to have been
altogether absent, and the frontal bones are relatively small.
The prootic bones are, as usual, situated in front of the ex-oc-
cipitals, and between the latter and them there may sometimes
be discerned a conical bone with a broad base, which appears
to be fitted in between the ex-occipital and the prootic. If
this bone were not so large, it miglit well be regarded as a
stapes, but it is possible that, as Cuvier suggests, it answers
to the separate opisthotic of the Chelonia,
. In the naso-premaxillary segment, the nasal bones, con-
tinuing the direction of the frontals, attain considerable size,
but the premaxillng make up by far the greater part of the
snout. The maxillae are reduced, as in birds, to comparatively
small and slender rod-like bones, bounding only a fraction of
the gape. The vomers are elongated, and situated in the
middle line on the underside of the snout.

The nostrils are small apertures close to the orbits,
bounded by the nasal, lachrymal, and premaxillary bones.

On each side of the frontal there is a large prefrontal,
which passes back above to meet the post-frontal, and thus
bound the orbit. Below, the maxilla is connected with a
jugal. From the post-frontal to the jugal, the posterior mar-
gin of the orbit is constituted by a distinct, curved, postorbi-
tal bone (Fig. 76, A, I^i. 0). A broad and flat quadrato-jugal
( Q:h) passes from the end of the jugal to the lower end of the
quadrate, and covers in the lower and posterior part of the
infra-temporal fossa. The space between this bone, the post-
orbital, the post-frontal and the squamosal, is occupied by
another flattened bone (Fig. 76, A, St.)^ which Cuvier calls
the temporal, but which does not appear to have any precise
homologue among other Reptilia. The squamosal bone is
very large and stout, and forms the postero-external angle of

212 THE ANATOMY OF VEETEBRATED ANIMALS.

the skull. From this point it sends a process forward to meet
the post-frontal, inward to unite with the parietal, and down-
ward to become connected with the pterygoid. A strong and
stout quadrate bone is connected wdth the exterior of the
skull, and presents a pulley-like surface to the articular piece
of the mandible.

On the under-surface of the skull the long and slender
palatine bones are seen, bounding the posterior nares, which
are situated far forward. Behind, and separated by an inter-
val traversed by the rostrum of the basisphenoid bone, the
very large pterygoids commence, by slender and pointed ends,
w^hich lie on the inner side of the palatine bones at the level
of the posterior nares. They then widen, and passing back-
ward with a slight outward curvature, on each side of the
sphenoidal rostrum, end in three processes — one which con-
nects itself with the basisphenoid, another passes outward and
backward to the quadrate, while the third runs upward to the
squamosal bone.

The lower jaw is composed of two rami, which unite,
anteriorly, in a very long symphysis. Each ramus is com-
posed of the normal six pieces, the splenial being remarkably
long, and entering extensivel}^ into the symphysis.

We have no very clear knowledge of the structure of the
hyoidean apparatus in this reptile.

The pectoral arch (Fig. 76, E) consists, upon each side, of
a narrow scapula ('S'c), having the direction usual in Lacer-
tilia^ and a broad coracoid (Co.), the inner edge of which does
not overlap its fellow, but meets it throughout in the middle
line, as in Plesiosaurus j so that, in this genus also, the rhom-
boiclal part of the sternum appears to have been absent or
/ery small.

But there is a very distinct T-shaped interclavicle [I. Cl.),
the backward prolongation of which is received between the
anterior ends of the coracoids, while its horizontal bar is very
closely united with the inner ends of two stout curved clav-
icles ( CI.), the outer extremities of which abut against, and
are no less closely connected with, the upper part of the an-
terior edge of each scapula. This arrangement of the clav-
icles and interclavicle presents interesting conditions inter-
mediate between those observed in JVbthosatD^cs, on the one
hand, and those common in the Lacertllla, on the other.

The scapula and coracoid give rise by their junction to a
glenoidal cavity, into which the tliick head of the very short
prismatic humerus (Fig. 70, B, TI) is received. The distal

THE ICHTHYOSAURIA, 213

end of the humerus presents two facets, which articulate with
a couple of short flattened polygonal bones, which represent
tlie radius and the ulna (7?, U). To these succeed two rows
of smaller polygonal ossicles in the place of a carpus : three,
representing the radiale, inter medimn^ and ulnar e (r. i. ii.)^
lie in the proximal row, and three or four carpalia ( Q:>.) in
the distal row. With the distal carpal bones are connected,
by means of the metacarpal ossicles [Wc), longitudinal series
of very numerous polygonal bones, adapted together by their
edges, and becoming gradually smaller toward the distal ex-
tremity of each series. The number of complete series does
not exceed five, and may be reduced to three — so that the
paddle may be pentadactyle, tetradactyle, or tridactyle. An
apparent multiplication of the number of digits arises from
two causes : First, the occasional bifurcation of some of the
digits ; secondly, the superaddition of marginal hones * to the
radial and to the ulnar edges of the manus [in.i/., m.r.). There
is thus formed a paddle, which is unlike either that of a Ce-
tacean, or that of a Plesiosaiirus^ or that of a Turtle — depart-
ing more than any of these structures from the ordinary form
of vertebrate limb.

There is no trace of any sternum behind the pectoral arch,
but the abdominal walls were strengthened by a number of
transverse arcuated bones, similar to those observed in the
Plesiosauria^ though not so strong. Each is composed of a
median piece with pointed ends, and of some three, or more,
lateral pieces, overlapping each other's ends, on each side,

(Fig. 76, C, Y'^') .

The pelvis (Fig. 76, F) is not connected by bone with the
vertebral column. It consists of an ilium (jT/.), an ischium
(J^.), and a pubis {JPh.)^ uniting together to form an acetabu-
lum, while the pubis and ischium of each side meet in the mid-
dle line. The ischium is a narrow and almost rod-like bone, the
pubis is somewhat broader, especially at its symphysial end.

The hind-limb (Fig. 76, D) has substantially the same
structure as the fore-limb, but is always smaller, and generally
of much less size.

The only other bony structure apiDertaining to IchtJiyosau-
nis that need be noticed, is a circle of plates developed in the
sclerotic of the enormous eye, which is frequently met with in
a very perfect state of preservation.

* 1 leave open the question whether these series of marginal ossicles are
remains of the digits of a pel} dactyle manus, such as exists in the Elasmo*
branch fishes.

214 THE ANATOMY OF VERTEBRATED ANIMALS.

It is possible that the Ichthyosauria occur in the Trias ;
they abound in the Lias and in other rocks of Mesozoic date,
up to, and includin!Xj the Chalk.

Some attain gigantic dimensions, and many species have
been founded by the differences in form and proportion of the
body and of the teeth ; but no one form is sufficiently different
from the rest to justify its separation as a distinct genus.
They may be roughly grouped into such as have relatively
short snouts and short paddles, with four carpalia {I. inter'
medius, communis^ etc.) ; and such as have longer snouts, long
paddles, and three carpalia {I. longlrostris, tenuirostris^ pla-
tyodon).

VI. The Crocodilia. — Crocodiles, the highest living Rep-
tilla, are Lacertilian in form, with long tails and four well-de-
veloped limbs, the anterior pair being the shorter, and pos-
sessing five complete digits, while the hind-feet are four-toed.
With a single exception, the living species have nails on the
three preaxial (radial and tibial) digits, so that two digits are
without nails on the fore-foot, and one on the hind-foot. The
feet are webbed, but the degree to w4iich the web is developed
varies greatly. The nostrils are situated at the end of the
long snout, and can be closed. The tympanic membranes are
exposed, but a cutaneous valve, or earlid, lies above each, and
can be shut down over it. All are partially aquatic in habit,
and some (the Ga vials) are completely so. None of the exist-
ing genera are marine, though many ancient Crocodilia inhab-
ited the sea.

The dermal armor is composed of scutes covered by epi-
dermic scales of corresponding form. When the armor is
complete — as in Caiman and Jacare alone among existing
Crocodilia, in Teleosaurus and Stagonolejns among extinct
forms — it consists of transverse rows of quadrate bony plates,
disposed so as to form a distinct dorsal and ventral shield,
separated by soft integument, in the trunk, but united into
continuous rinses on the tail. The scutes of the same row are
united suturally ; those of each row overlap their successors,
which present smooth facets to receive their under-surfaces.
In existing Crocodilia, in the extinct Crocodilus Hasting sloe,
and in Stagonolepis, each ventral scute consists of two pieces,
a small anterior and a large posterior, united by a suture.
The scutes always exhibit a pitted sculpture, and those of the
dorsal region are ridged longitudinally, while the ventral
scales are always flat. More or fewer dorsal scutes exist in

THE CROCODILIA. 216

all crocodiles, and those upon the neck sometimes form dis-
tinct " nuchal " and " cervical " groups, distinct from the dor-
sal shield. The dorsal scutes do not always overlap, and the
ventral scutes are absent, or incompletely ossified, in most ex-
istino; Crocodilia.

In these reptiles the vertebral column is always thoroughly
ossified, and marked out into distinct cervical, dorsal, lumbar,
sacral, and caudal regions. The number of the presacral ver-
tebrae is twenty-four; that of the sacral, tw^o, in all the recent
forms, and probably in the extinct genera also. The number
of the caudal vertebrae varies, but is not less than thirty-five.
The number of the cervical, dorsal, and lumbar vertebrae varies ;
but there are usually nine of the first, eleven or twelve of the
second, and four, or three, of the third description.

In existing Crocodilia all the vertebrae, except the atlas
and axis, the two sacrals, and the first caudal, are procoelous.
The majority of the pre-cretaceous Crocodilia have the corre-
sponding vertebrae amphicoelous, the concavities of the centra
being very shallow. One genus, Streptosj^ondylus, which is
perhaps Crocodilian, has the anterior vertebrae opisthocoelous.
It is characteristic of the Crocodilia^ that the centra of the
vertebrae are united by fibro-cartilages, and that the neurocen-
tral sutures persist for a long time, or throughout life.

The atlas is composed of four pieces, an upper median
piece — which is sometimes divided into two, and is developed
in membrane apart from the rest — being added to the three
pieces found in Lacertilia and Chelonia. A large odontoid
bone is closely united to, but not anchylosed with, the anterior
flat face of the second vertebra. A pair of elongated, single-
headed ribs are attached to the inferior piece of the atlas, and
another similar pair to the os odontoidum and to the second
vertebra, by distinct capitular and tubercular processes. The
other cervical vertebrae all possess ribs with distinct and long
capitula and tubercula — the latter attached above the neuro-
central suture to the neural arch, the former to the centrum
below the neurocentral suture. The body of each cervical
rib, after the second, and as far as the seventh or eighth, is
short, and prolonged in front of, as wxU as behind, the junction
of the capitulum wnth the tuberculum ; and the several ribs
lie nearly parallel with the vertebral column, and overlap one
another. The ribs of the eighth and ninth cervical vertebrae
are longer, and take on more the character of the dorsal ribs,
the ninth having a terminal cartilage.

The points to which the capitula and tubercula of the riba

216 THE ANATOMY OF YERTEBRATED ANIMALS.

are attached are raised into tubercles ; and, by degrees, these
become elongated into distinct capitular and tubercular pro-
cesses, between which, in the third to the ninth vertebrse, the
neurocentral suture passes. But in the tenth and in the elev-
enth vertebrse, the capitular process, which lies nearer the
neurocentral suture in the posterior than in the anterior cervi-
cal vertebrae, rises upon the body of the vertebra to the level
of the neurocentral suture, bv which it is traversed, and the
tubercular process becomes longer than it. (See Fig. 5, p. 19.)
The terminal cartilage is united with the sternum by a sternal
rib, which may become more or less completely converted into
a cartilage-bone, and is articulated with the vertebral rib.

In the twelfth vertebra a sudden change in the character
of the transverse processes takes place. There is no longer a
capitular, distinct from a tubercular, process, but one long
" transverse process " takes the place of both. A sort of step
in the base of this process bears the capitulum of the rib, and
answers to the capitular process of the cervical vertebrse, Avhile
the outer end of the process articulates with the tuberculum
of the rib, and represents the tubercular process. The neuro-
central suture, in this and the succeeding dorsal vertebrae, lies
below the root of the transverse process, which, therefore, is
w^hoUy a product of the neural arch. Neither the capitular
processes, nor that part of the dorsal transverse process which
represents them, have distinct centres of ossification.*

In the succeeding dorsal vertebrse the " step " of the trans-
verse process gradually moves outward, until at length it be-
comes confounded with the tubercular facet, and a correspond-
ing change takes place in the proximal ends of the ribs, in the
hindermost of w^hich the distinction between capitulum and
tuberculum is lost.

The lumbar vertebrae have long transverse processes which
arise from the neural arches, i. e., above the neurocentral su-
ture.

The centra of the two sacral vertebrse have their applied
and firmly-united faces flat, their free faces concave ; conse-
quently, the first has the anterior face concave and the poste-
rior flat, w^hile the second has the anterior surface flat and the
posterior concave. Each sacral vertebra has a strong rib ex-
panded at its distal end ; and wedged in at its proximal end,

* Thus, if it be apart of tlie definition of a '-'• parajyopliyds^'' tliat it is anto-
eenous, there are no parapophyses in the vertebras ot the Crocodilia ; and if it
be part of the definition of a " parapophysis " that it arises from the centrum,
the dorjjal vertebraR of the Crocodilia nave no parapophyses.

THE CKOCODILIA. 217

between rougH sutural surfaces furnished by the neural arch
above and the centrum below.

The first caudal vertebra is biconvex, but all the others are
procoelous ; those of the anterior moiety of the tail have long
ribs fixed in between the neural arches and centra, as in the
sacrum, and becoming anchylosed in that position. Chevron-
bones are attached to the posterior edges of the centra of the
vertebrae, except that of the first, and those of the posterior
part of the tail.

From seven to nine of the anterior dorsal ribs are united
with the sternum by sternal ribs, the form of which varies a
good deal in different GrocodlUa^ being sometimes narrow,
sometimes broad and flattened. An elongated plate of carti-
lage, which may be partially converted into cartilage-bone, is
attached to the hinder margin of several of the most anterior
ribs, above the junction between the ossified and the cartilagi-
nous part of the vertebral rib. (Fig. 5, P.u.) These are the
so-called " uncinate processes," which also exist in Hatteria^
and reappear in Birds.

The sternum consists of a rhomboidal plate of cartilage-
bone, with the posterolateral edges of which two pairs of
sternal ribs articulate. The posterior angle of the plate is con-
tinued into a median prolongation, which, at length, divides
into two curved divergent cornua. From five to seven pairs
of sternal ribs are united with the prolongation and its cornua.
A long and slender interclavicle lies in a groove of the middle
of the ventral face of the rhomboidal part of the sternum.

In the ventral wall of the abdomen, superficial to the recti
muscles, lie seven transverse series of membrane-bones, which
are termed " abdominal ribs ; " though it must be recollected
that they are quite distinct from true ribs, and rather corre-
spond with the dermal ossicles of the Lahyrinthodonta. Each
series is composed of four elongated and more or less curved
ossicles, pointed at each end, and so disposed that inner ends
of the inner pair meet at an angle, open backward in the
middle line, while their outer ends overlap the inner ends of
the outer pair. The most posterior of these ossicles are
stronger than the others, and are closely connected with the
pubic cartilages.

In the Crocodilian skull the following are the chief pecu-
liarities which are worthy of especial notice :

1. There is an interorbital septum, and the presphenoidal
and orbitosphenoidal regions remain cartilaginous, or verT
incompletely ossified.
10

218

THE ANATOMY OF YERTEBRATED ANIMALS.

I'N

Fig. 77.— Longitudinal and vertical section of the hinder part of the skull of a CrotXfdila
Eu^ Eustachian tube : P jV, posterior nares ; P, pituitary fossa.

2. All the bones of tlie skull (except the mandible, stapes,
and hyoid) are firmly united by sutures, which persist through-
out life.

3. There are large parotic processes. Both the upper and
the lower temporal arcades are completely ossified, and formed
by post-frontal, squamosal, jugal, and quadrate- jugal bones;
supra-temporal, lateral-temporal, and post-temporal fossa3 are
formed, as in the Lacert'dia^ though their relative sizes are
very different.

4. The maxillary and the palatine bones develop palatine
plates, which unite suturally in the middle line, and separate
the nasal passages from the cavity of the mouth, as in Mam-
9nalia / and in all existing Crocodiles, but not in IHeosauriis
or JBelodon^ the pterygoids are also modified in tlie same way
(as in Mymercophaga among Mammals), so that the posterior
nares are situated very far back beneath the base of the skull.

5. In consequence of the development of these palatine
plates of the maxillary and palatine bones, the two vomers
are, in most Crocodiles, invisible upon the under-surface of
the bony roof of the mouth.

THE CROCODILIA. 219

6. There are larger alispbenoids, but the orbitosphenoids
are absent or nidimentarj.

7. There is no parietal foramen.

8. The quadrate bone is very large, and fixed immovably
to the walls of the skull, as in the Ghelonia ; and, as in the
latter, the pterygoid bone is firmly connected with the base
of the skull, and united only with the upper and inner surface
of the quadrate bone.

9. The pterj^goid sends down a large free process, against
the broad outer edge of which the inner surface of the mandi-
ble plays.

10. The tympanic cavity is completely bounded by bone.
The pro5tic and opisthotic (which is united with the ex-oc-
cipital) form its inner walls, the quadrate its outer wall, the
squamosal and post-trontal its roof, and the quadrate, the basi-
occipital, and basisphenoid its floor. The two tympana are
placed in communication with the cavity of the mouth by three
canals — one large, opening in the middle line ; and two smaller
ones at the sides, on the base of the skull, behind the posterior
nares. The large canal passes up between the basisphenoid
and basi-occipital, and divides between those bones into a
right and left lateral canal. Each lateral canal subdivides
into an anterior branch, which traverses the basisphenoid, and
a posterior, which passes up in the basi-occipital. The
posterior branch receives the narrow lateral canal of its side
(which runs vertically up to it), and then opens into the
posterior part of the floor of the tympanum. The anterior
branch opens into its anterior wall.

The tympanic cavities of embryonic Crocodiles communi-
cate with the mouth by wide and simple apertures, and the
complicated arrangement of canals just described results from
the great downward development of the basisphenoid and basi-
occipital, and their encroachment upon these apertures on the
inner side, while the quadrate bone narrows them on the outer.

In adult Grocodllia^ air-passages extend from each tym-
panum to that of the opposite side, through the bones which
form the roof of the posterior region of the skull. On the
other hand, they excavate the quadrate bone, whence the
air passes through a membranous tube into the hollow ar-
ticular piece of the mandible. The hyoidean apparatus is
greatly simplified, consisting only of a broad plate of cartilage,
which may become partially ossified, and of two ossified
cornua which are not directly connected with the skull. A
minute styliform cartilage, which lies in close proximity with

220 THE ANATOMY OF YERTEBRATED ANIMALS.

the port to dura, on the upper part of the posterior face of the
quadrate bone, represents the stylohyal, or proximal end of
the hyoidean arch.

The pectoral arch has no clavicle, and the coracoid has no
distinct epicoracoidal element, nor any fontanelle. The carpus
consists proximally of two elongated and somewhat hour-glass-
shaped bones, articulated respectively with the radius and the
ulna. The radial is the larger, and is partially articulated
with the ulna. Behind these, and directed transversely, lies
another curved ossification, the upper concave face of which
articulates with the ulna. It is united with the latter bone
on the one hand, and with the fifth metacarpal, on the other,
by strong ligaments, and represents a pisiform bone. Distally,
there lies on the ulnar side the so-called lenticular bone, an
oval ossicle interposed between the ulnar proximal carpal and
the second, third, fourth, and fifth metacarpals, the last three
of which it supports altogether. On the radial side, a disk
of cartilage, which never becomes completely ossified, is con-
nected by ligament with the lenticulare, and is interposed
between the radial proximal bone and the head of the meta-
carpal of the pollex. From the ulnar side of the head of this
bone a cartilaginous ligamentous band proceeds, over the head
of the second metacarpal, to the radial side of the lentlculare.

The three radial digits are much stronger than the two
ulnar, and the numbers of the phalanges are 2, 3, 4, 4, 3,
countino' from the radial to the ulnar side.

The pelvis (Fig. 78, C) possesses large ilia, which are firmly
united with the expanded ends of the strong ribs of the sacrum.
Tiie ischium unites with its fellow in a median ventral symphysis,
and, with the ilium, forms almost the whole of the acetabulum.

The pubes take hardly any share in the formation of the
latter cavity in the adult. Their axes are directed forward
and inward, and they coalesce in the middle line ; but as the
inner, or median, moiety of each jDubis remains cartilaginous,
or imperfectly ossified, the bones, in imperfectly prepared
skeletons, appear as if they formed no symphysis.

Tlie tarsus presents, proximally, an astragalo-navicular
bone and a calcaneum, which are less closely united than in
the Lizards. The latter bone has a large calcaneal process on
Its posterior face, the Crocodile being the only Sauropsid verte-
brate in which such a process is developed (Fig. 78, C Ca,).

Two rounded distal tarsal bones, of which the fibular is
much the larorer, lie between the calcaneum and the third,
fourth, and rudimentary fifth, metatarsals. A thin plate of

THE CROCODILIA. 221

cartilage is interposed between the distal end of the astragalo-
navicular and the second metatarsal, and unites with the head
of the first metatai'sal.

As in the manus, the three, pre-axial, clawed, digits are
stronger than the others. The fifth is represented only by an
im23erfect metatarsal. The numbers of the phalanges are
2, 3, 4, 4, counting from the tibial to the fibular side.

In the Crocodilla the teeth are confined to the premaxillfe,
maxillas, and dentary part of the mandible. They are simple
in structure, have large pulp-cavities, are lodged in distinct
alveoli, and are replaced b}'' others developed upon their inner
sides. The development of the new tooth causes absorption
of the inner wall of the base of the old one, and the replacing
tooth thus comes to lie within the pulp-cavity of its predeces-
sor. The teeth vary much in shape, having either long, curved,
and acute, or short and obtuse, or almost globular and straight,
crowns. Very often they possess sharp anterior and posterior
edges, which may be finely serrated.

The Crocodllia are to be found in the rivers of all con-
tinents and the larger islands in the hotter parts of the world.
None of the existing species are truly marine, though many
of the extinct species were. They are first known to occur in
strata of Triassic age, and abound, under forms which differ
but little from some of those which now exist, in the Mesozoic
^nd Cainozoic formations.

They may be divided into the following groups :

A. With procoelous presacral vertebrae, and posterior nares bounded
below by the pterygoids. (All existing Crocodilia, and the fossil
forms of cretaceous and later formations, are included in this division.)

a. The nasals enter into the formation of the nasal aperture.

a. The head short and broad. The teeth very unequal ; the first

and fourth of the mandibles biting into pits of the upper
jaw. The premaxillo-maxillary suture straight or convex
forward. The mandibular symphysis not extending beyond
the fifth tooth, and the splenial element not entering into it.
The cervical scutes distinct from the tergal.

1. Alligatoridoe.

Alligator. Caiman. Jacare.

b, The head longer. The teeth unequal. The first mandibular

tooth biting into a fossa ; the fourth, into a groove, at the
side of the upper jaw. The premaxillo-maxillary suture
straight or convex backward. The mandibular symphysis
not extending beyond the eighth tooth, and not involving
the splenial elements. The cervical scutes sometimes dis-
tinct from the tergal, sometimes united with them.

2. Crocodilidce.

Crocodilus. Jfecistops.

222 THE ANATOMY OF VERTEB RATED ANIMALS.

b. The nasals are excluded from the external nasal aperture. The head
very long; the teeth subequal. Both the first and the fourth
mandibular teeth bite into gi'ooves in the margin of the upper jaw.
The premaxillo-maxillary suture acutely angulated backward. The
mandibular symphysis extends to at least the foui'teenth tooth, and
the splenials enter into it. The cervical and tergal scutes form a
continuous series.

3. Gavialidce.

Rhynchosuclius. Gavialis.

B. With the presacral vertebrae amphicoelous (the anterior vertebrae
sometimes opisthocoelous (?) ); and the posterior nares bounded by
the palatines, the pterygoids not being united below. (All these
Crocodiles are extinct and pre-cretaceous.)

a. "With the external nares terminal.

4. Teleosauridce.

Teleosawus. Goiiiopholis.

Sly^eptospondylus. Stagonolcpis. Galesanrus (?).

b. With the external nares on the upper part of the base of the snout

near the orbits.

5. BelodontidcB.

Belodon.

There is a large number of extinct Heptilia which resemble
the CrocodUla in the characters of their pre-sacral vertebrjs,
but differ from them, and resemble Laceriilla Chelonia, or
Birds, in other respects.

These are the Dlcynodontia^ the Ornithoscellda^ and the
J^erosauricL

VII. The DiCY]sroDO]srTiA. — Dicynodon and Oudenodon
are lacertiform animals, sometimes of large size, with crocodil-
ian vertebrge, four or five of which are anchjlosed together to
form a strong sacrum. The skull is massive and lacertilian in
most of its characters ; but the jaw^s are like those of the
Chelonia, and w^ere doubtless cased in a horny beak. Never-
theless, most of the species possess two great tusks, which
grow from persistent pulps, lodged in a deep alveolus of either
maxilla. The limbs appear to have been subequal and massive,
with short and stout feet. The scapula and coracoid are
simple and expanded, and there seems to have been no clav-
icle. The pelvis is very strong, with w'idely-expanded ilia,
ischia, and pubes. The two latter meet in a median ventral
symphysis, and the pubis and ischium of each side meet and
obliterate the obturator foramen. The limb-bones are lacer-
tilian in character.

Remains of these Reptiles have hitherto been found only
in strata, which probably belong to tlie Triassic formation, in
India and South Africa, and the Ural Mountains.

THE DICYNODONTIA-

Fig. T8. — ^Tlie pelvis and hind-limb of, A., DromcBUS ; B., an omithoscelid reptile, such as
Iguanodon, or Hypsilophodon ; and C, a Crocodile. The bird's limb is in its natural
position, as is that of the Omithoscelid, though the metatarsus of the latter may not, in
nature, have been so much raised. The Crocodile's limb is purposely represented in an
unnatural position. In nature, the femur would be turned out nearly at right angles to
the middle vertical plane of the body, and the metatarsus would be horizontal. The letters
are the same throughout. 7Z, ilium ; Zs, ischium ; Pb, pubis ; a, anterior process, &,
posterior process, of the ihum ; T)\ inner trochanter of the femm- ; T, tibia ; F, fibula ;
As^ astragalus ; Ca, calcaneum. /., //., ///., IV.., the digits.

VIII. The Ornithosceltda. — The very remarkable extinct
reptiles which constitute this group, present a large series of
modifications intermediate in structure between existing Hep-
tilia and Aves.

224 THE ANATOilY OF YERTEBRATED ANIMALS.

This transitional character of the Ornithoscelidan skeleton
is most marked in the pelvis and hind-limbs.

If the pelvis of any existing reptile be compared with that
of any existing bird, the following points of difference will be
observed :

1. In the reptile (Fig. 78, C), the ilium is not prolonged
in front of the acetabulum; and the acetabulum is either
wholly closed by bone, or presents only a moderate-sized
fontanelle, as in the Crocodilia.

In the bird (Fig. 78, A.), the ilium is greatly prolonged in
front of the acetabulum, and the roof of the acetabular cavity
is a wide arch, the inner wall of that cavity remaining mem-
branous. The anterior pier of the arch, or prae-acetabular pro-
cess, extends farther downward than the posterior pier, or
post-acetabular process.

But, in all the Omithoscelida, the ilium extends far in
front of the acetabulum, and furnishes only a widely-arched roof
to that cavity, as in birds. It retains a reptilian character in
the further proportional extension of the post-acetabular pro-
cess downward (Fig. 78, B.).

2. The ischium, in the reptile (Fig. 78, C), is a moderately
elongated bone, which becomes connected with the pubis in
the acetabulum, and extends downward, inward, and somewhat
backward, to unite with its fellow in a median ventral sym-
physis. The obturator space is not interrupted by any for-
ward process of the outer and anterior half of the ischium.

In all birds (Fig. 78, A.), the ischium is elongated and in-
clined backward, the backward direction being least marked
in Apteryx^ and most in Hhea. The ischia never come to-
gether directly in a median ventral symphysis, though they
unite dorsally in Hhea. The anterior edge of the external, or
acetabular, half of the ischium very generally sends off a pro-
cess which unites with the pubis, thus dividing the obturator
space.

In all the Ornitlioscelida (Fig. 78, B.), in which I have
been able to identify the bone {Thecodoiitosaurus^ Terato-
srmrifs, 3fegalosaurus^ Iguanodon^ Stenopdyx^ Hadrosaiirus^
IlypsUophodon), the ischium is greatly elongated. In Iguaii'
odon it has the obturator process characteristic of the same
bone in Birds ; and I imagine that the same process is seen in
Coinpsognathus. In Hypsilophodon there can be no mistake
'i,bout the matter, and the remarkable slenderness and prolon-
gation of the ischium give it a wonderfully ornithic character.

THE ORNITHOSCELIDA. 225

Til Iguanodon the slenderness and prolongation are even car-
ried beyond wliat are to be seen in Birds. I am disposed to
think, however, that, as was certainly the case in Hyj^silojyho-
don^ the ischia united in a median ventral symphysis in all the
Orn ith oscelida,

3. In all reptiles the pubis is inclined forward, as well as
downward, toward the ventral median line. In all, except the
Crocodile, it takes a considerable share in the formation of the
acetabulum ; and the ossified pubis unites directly with its
fellow in the middle line.

The pubes of Gomi^sognatlius are, unfortunately, obscured
by the femora. They seem to have been very slender ; and to
have been directed forward and downward, like those of Liz-
ards. Some lizards, in fact, have pubes which, if the animal were
fossilized in the same position as Compsognatlms^ would be very
similar in form and direction. Hypsilopliodon^ however, affords
unequivocal evidences of a further step toward the bird. The
pubes are not only as slender and elongated as in the most
typical bird, but they are directed downward and backward
parallel with the ischia, thus leaving only a very narrow and
elongated obturator foramen, which is divided by the obtura-
tor process.

It remains to be seen how far the hypsilophodont modi-
fication extended among the OrnitJioscelida. The remains of
Compsognathus and of &tenopelyx tend to show that it was
by no means universal.

As to the hind-limb, in existing reptiles —

1. The proximal end of the tibia has but a very small, or
quite rudimentary, cnemial crest, and it presents no ridge for
the fibula on its outer side.

2. The flattened sides of the distal end of the tibia look,
the one directly forward, or forward and inward ; and the
other backward, or backward and outward. And when the
posterior edges of the two condyles of the proximal end of the
tibia rest on a flat surface which looks forward, the long axis
of the distal end is either nearly parallel with that surface, or
is inclined obliquely from in front and without, backward and
inward.

3. There is no depression on the anterior face of the tibia
for the reception of an ascending process of the astragalus.

4. The distal end of the fibula is as large as, or larger than,
the proximal end, and articulates largely with a facet on the
outer part of the astragalus.

5. The astragalus is not depressed and flattened from above

226 THE ANATOMY OF VERTEBRATED ANIMALS.

downward, nor does it send a process upward in front of the
tibia.

6. The astragalus remains quite free from the tibia.

In all these respects, the leg of any existing bird (see
Fig. 78) is very strikingly contrasted with that of the
reptile :

1. The proximal end of the tibia is produced forward and
outward into an enormous cnemial crest, in all walking and
swimming birds (Fig. 78, A.) ; and, on the outer side, there
is a strons: rid^-e for the fibula.

2. When the posterior edges of the condyles of the tibia
rest upon a flat surface, the one flat face of the distal end of
the bone looks outward as well as forward, and the other in-
ward as well as backward. Further, the long axis of the dis-
tal end is inclined, at an angle of 45° to the flat surface, from
within and in front, backward and outward, thus exactly re-
versing the direction in the reptile.

3. There is a deep longitudinal depression on the anterior
face of the distal end of the tibia, which receives an ascendinjr
process of the astragalus.

4. The distal end of the fibula is a mere style, and does not
articulate with the astragalus.

5. The astragalus is a much-depressed bone, with a concave
proximal, and a convex, pulley-like, distal, surface. A process
ascends from its front margin in the groove on the front face
of the tibia. This process is comparatively short, and perfo-
rated by two canals for the tibialis anticus and extensor com-
tiiunis, in the Fowl ; while in the Ostrich and Emeu it is ex-
tremely long and not so perforated.

6. The astragalus becomes anchylosed with the tibia
(though it remains distinct for a long time in the Ostrich and
lihea^ and in some breeds of fowls).

In the Ornithoscelida :

1. Tlaere is a great cnemial crest and a ridge for the fibula.

2. The disposition of the distal end of the tibia is literally
that observed in the Bird.

3. There is a fossa for the reception of the ascending pro-
cess of the astragalus.

4. The distal end of the fibula is much smaller than the
proximal, though not so slender as in Aves.

5. The astragalus is altogether similar to that of a bird,
with a short ascending process.

6. The astragalus appears to have remained distinct from
the tibia throughout life in Igiianodon, Megalosaurus^ and

THE ORNITEOSCELIDA. 227

many other genera ; but it seems to liave become anchylosed
in CompsognathuSj OriiitJiotarsus^ and Euskdosaurus.

The reptiles belonging to this group are for the most part
of very large size, and some of them, as the Iguanodon^ are
among the largest of known terrestrial animals. They oc-
cur throughout the whole range of the Mesozoic formations,
being represented by Thecodooitosaurus^ JPalmosaurus^ Tera-
tosaurus^ JPlatmosaurns^ and other genera in the Trias ; by
Scelidosaums in the Lias ; by 3fegcdosauriis, Poikiloplenron^
Euskelosaurus^ Hylmosaurus^ Polacanthus^ Acanthopliolis^
Jguanodon^ Iladrosauriis^ Trachodon. and Laelaps in the
middle and upper Mesozoic strata.

There is no evidence that Megaloscmrus^ or Iguanodon^
possessed any dermal armor; but several genera (e.g., Sceli-
dosaiirus, Uglceosaurus, and Aca)itho2)holis) had osseous
dermal scutes, sometimes produced into prodigious spines.

The faces of the centra of the vertebras are slightly am-
phicoelous, or nearly flat ; but those of the anterior dorsal and
cervical regions seem, in some cases, to have been opisthocoe-
lous. The sacrum seems to have consisted of at fewest four
vertebrae, which in some [Scelidosaurus) are crocodilian, in
others {Megalosatcrus) take on a somewhat ornithic character.
The caudal region had many and long vertebrae, between
which the chevron-bones are attached. The rami of the chev-
ron-bones have their vertebral ends united by bone.

The thoracic vertebral ribs are very strong ; but the sternal
ribs and sternum are unknown. However, there is some rea-
son to think that the sternum was broad and exjDanded. Ab-
dominal dermal ribs are developed in some species, if not
in all.

The structure of the skull seems to have been intermediate,
in many respects, between the crocodilian and the lacertilian
types. In Iguanodon and Sypsilophodon^ the extremities of
the premaxilhie appear to have been edentulous and beak-like ;
and the symphysis of the mandible is excavated to receive the
beak, almost as in the mandible of a Parrot.

The teeth vary extremely, from the sharp, recurved, ser-
rated fangs of MegalosauTus^ to the broad grinders, wearing
down by mutual attrition, of Iguanodon, Their mode of im-
plantation varies, but they are not anchylosed to the jaws.

The scapula is vertically elongated, narrow, and devoid of
any acromial process ; the coracoid rounded and without fon*
tanelles or processes.

228 THE ANATOMY OF YERTEBRATED ANIMALS.

No Ornitlioscelidan is known to have possessed a clavicle.

The fore-limb is shorter, and often much shorter, than
the hind-limb. The structure of the manus is not certainly
known.

The femur usuallv has a strong^ inner trochanter : and its
distal end is particularly bird-like, in the development of a
strong ridge, which plays between the tibia and the fibula.

The metatarsals are elongated, and fit together in such a
way that they can hardly, if at all, move on one another. The
imier and outer digits are either shorter than the rest, or quite
rudimentary ; and the third digit is the longest, as in birds in
general.

The Or7iithoscelida are divisible into two sub-orders, the
Dinoscmria and the Compsognatlia. The type of the latter
division is the wonderful little extinct rej^tile, Comi^sogna-
thus^ W'hich differs from the Dmosauria in the great length
of the centra of the cervical vertebrae, and in the femur being
shorter than the tibia. It has a light bird-like head (provided
with numerous teeth), a very long neck, small anterior limbs,
and very long posterior limbs. The astragalus aj)pears to
have been anchylosed w4th the tibia, as in birds. A single
specimen only of this reptile has been obtained, in the Solen
hofen slates.

IX. The PTEEOSArpjA. — The fl}^ng Reptiles, which belong
to this group, and are commonly known as Pterodactj^ls, are,
and long have been, extinct, their remains occurring only in
Mesozoic rocks, from the Lias to the Chalk inclusively.

They are all remarkable for their proportionally long heads
and necks, and for the great size of the anterior limb, the
ulnar finger of which, enormously elongated and devoid of a
claw, appears to have supported the outer edge of an expan-
sion of the integument, like the patagium of a Bat (Fig. 79).

The vertebral column is distinctly divided into cervical,
dorsal, sacral, and caudal regions, the cervical vertebra3 being,
as in Birds, the stoutest of all. The atlas and axis are anchy-
losed together, at least in the cretaceous species. The other
cervical vertebrae, apparently not more than six or seven in
number, have low, or obsolete, spinous processes ; and, like
the vertebrae of the rest of the spine, are procoelous, and
have the neuro-central suture obliterated. The existence of
cervical ribs is doubtfuk From fourteen to sixteen vertebrae
intervene between the cervical and the sacral regions ; and
not more than one or two of the hindermost of them, if any,

TIIE FTEHOSAURiA.

229

are devoid of ribs. Tlie number of vertebraB anchylosed
together to form the sacrum, is not fewer than three, nor more
than six.

PiQ, 79. — The nearly entire sTceleton of Pterodactyliis spectaMUs (Von Mever), as shovri
by the two halves of a split block of lithographic slate, a, the left pre-pubic bone
on the right side this bone is not shown, and the ilium is exposed.

The tail is very short in Pterodactylus, and, in this genus,
all the vertebrae are movable upon one another ; but in Jthani-
phorhynchus^ it is extremely long, and the vertebrae are
immovably fixed by what appear to be ossified ligamentous
fibres.

The vertebral ribs are slender, and the anterior ones, at
any rate, have distinct capitula and tubercula. There are

230 THE ANATOMY OF VERTEBRATED ANIMALS.

ossified sternal ribs, and splint-like abdominal ribs. Tlie
sternum is broad, and, unlike that of other Reptilia^ is very
completely ossified, and bears a strong median crest on the
anterior part of its ventral surface. No median posterior pro-
longation has been observed in connection with it.

The brain-case is more rounded and bird-like than in the
other Reptilia^ and, in many other respects, the skull ap-
proaches that of birds. Thus, the occipital condyle is on the
base of the skull, not on its posterior face ; the cranial bones
anchylosed very early ; the orbits are very large, and the ex-
ternal nares are situated close to them. Tlie premaxillas are
very large, the maxilljB slender, and the dentary pieces of the
mandible are fused together into one bony mass, without any
trace of a symphysial suture.

The resemblance to birds is still further increased, in some
species, by the presence of wide lachrj^mo-nasal fossce between
the orbits and the nasal cavities, and by the prolongation of
the extremities of the premaxillse and of the symphysial part
of the mandible into sharp, beak-like processes, which appear
to have been covered vvith horny sheaths. But the reptilian
type is kept up by the presence of a distinct post-frontal, which
unites with the squamosal and thus gives rise to a supra-
temporal fossa. The post-frontal and the jugal unite behind
the orbit, in Lacertilian fashion ; and both the upper and the
lower jaws contain teeth. The sclerotic is supported by a ring
of bones, as in many other Sauropsida.

The scapula and the coracoid are wholly unlike these
structures in any other Sauropsida^ but are extremely similar
to the same parts in birds, and indeed to the shoulder-girdle
of the less reptilian Carinatm. The sca2:)ula is slender and
blade-like, and its long axis is inclined, at less than a right
angle, to that of the coracoid. The glenoidal surface is cylin-
droidal, concave from above downward, convex from side to
side. The coracoid, elongated and comparatively narrow, is
devoid of fontanelle, epicoracoid, or procoracoid.

No trace of any clavicle has been discovered.

The humerus has a great deltoid ridge or jorocess. Tlie
radius and ulna are equal in size and separate. There are
four distinct metacarpal bones, that on the ulnar side being
very much stronger, though not longer, than the others. An-
other styliform bone attached to the carpus does not appear
to have belonged to the metacarpal series. The radial meta-
carpal bears two phalanges ; the second, three ; the third, four,
BO that these represent the pollex and the succeeding digits

THE PTEROSAURIA. 231

of the Lizard's manus. The terminal phalanx of each of these
digits is strong and curved, and was doubtless ensheathed in
a horny claw. The fourth, like the corresponding digit in the
Crocodile, has four phalanges, the last of which is straight and
bears no nail. But these phalanges are enormously elongated
and of great relative strength. A strong process projects from
the dorsal side of the proximal end of the first phalanx, and
doubtless gave attachment to the tendon of a correspondingly
powerful extensor muscle. The articular surface below and
behind it is concave, and plays over the convex distal pulley
of the fourth metacarpal.

The pelvis is remarkably small. The ilia are elongated
bones, produced both anteriorly and posteriorly, as in Birds ;
but the rest of the pelvis is not at all ornithic. The flat and
broad ischia appear to be united with the pubes into wide
bony plates, which pass, at right angles with the ilia, to their
median ventral symphysis. A large spatulate bone articulates
with each pubis near the symphysis, and seems to be an exag-
geration of the pre-pubic process of Lacertilia and Chelonia.
Or it may be (though I do not think this very probable) that
the broad flat plates correspond almost altogether to the ischia,
and that the spatulate ossifications are the pubes ; in which
case the structure of the pelvis would be a sort of extreme ex-
aggeration of that observed in the Crocodilia.

The hind-limb is small compared with the fore-limb. The
fibula is imperfect, and appears to coalesce with the tibia at
its distal end. The structure of the tarsus requires further
elucidation. In some Pterosauria there seem to be only four
digits, with, perhaps, a rudiment of a fifth, in the pes ; but
others, such as Mhamphorhynchus Gemmingi^ have five digits
in the foot. Where there are only four, each digit is termi-
nated by a curved and pointed ungual phalanx, and the num-
ber of the phalanges from the tibial to the fibular side is 2, 3,
4, 5. These digits, therefore, are the hallux, and the three which
immediately follow it ; and the rudimentary digit is the
fifth.

The lon^ l,ones of the Pterosauria have thin walls, enclos-
ing a large cavity, which appears to have contained air, as in
many birds ; and pneumatic foramina are visible on the sides
of the vertebrae.

The remains of more than twenty species of Pterosauria
have been discovered. Some of them are exquisitely preserved
in the fine matrix of the lithographic stone of Solenhofen.

They are thus grouped into genera ;

232 THE ANATOMY OF VERTEBRATED ANIMALS.

A. With two joints in the ulnar digit of the manus.

Ornitkopterus.

B. "With four joints in the ulnar digit.

a. The jaws strong, pointed, and toothed to their anterior ex-

tremities. The tail very short. The metacarpus usually
longer than half the length of the antebrachium.
IHerodadylus.

b. The extremities of the jaws produced into toothless beaks>

probably ensheathed in horn. The tail very long. The meta-
carpus shorter than half the length of the antebrachium.
a. All the mandibular teeth similar.
Hhamphorhynclius.

h. The posterior teeth for the most part very short. The
anterior long,

DimorpJiodon.

I am mucli inclined to suspect that the fossil upon which
the genus OmitliopUrus has been founded, appertains to a true
Bird

CHAPTER VL

THE CLASSIFICATION AND THE OSTEOLOGY OF BIRDS.

The class Aves. — Though this class contains a great
number of specific forms, the structural modifications which
they present are of comparatively little importance ; any two
birds which can be selected difi'ering from one another far less
than the extreme types of the Lacertilia, and hardly more
than the extreme forms of the Chelonia^ do. Hence the char-
acters by which the following groups are separated appear
almost insignificant when compared with those by which the
divisions of the Reptilia are indicated.

A. The metacarpals not anchylosed together. The tail longer than the

body.

I. — SAURURiE.

1. ArchceopterygidcB.

B. The metacarpals anchylosed together. The tail considerably shortei

than the body.

k. The sternum dcYoid of a keel.

II. — Ratit^.

a. The wing with a rudimentary, or very short, humerus and
with not more than one ungual phalanx.
a. A hallux.

2. Apterygidce (The Kiwis).
i8. No hallux.

3. Dinornithidce (The Moas).

4. Casuaridce (The Cassowaries).

h. The wing with a long humerus and with two ungual
phalanges.

a. The ischia uniting immediately beneath the sacrum,
and the pubes free.

5. RheidcB (The American Ostriches).

^ i8. The ischia free and the pubes uniting in a ventral

symphysis.

6. Struthionidce (The Ostriches).
B. The sternum provided with a keel.*

* The keel is rudimentary in the singular Parrot Strigopa,

234 THE ANATOMY OF VERTEBKATED ANIMALS.

III. — Caeinat^.

a. The vomer broad beliind, and interposing between the
ptei-ygoids, the palatines, and the basisphenoidal rostrum

{DromcEognathce.')
'7. Tinamomorphce (The Tinamous).

b The vomer narrow behind ; the pterygoids and palatines
articulating largely with the basisphenoidal rostrum.

a. The maxillo-palatines free.*
i. The vomer pointed in front.

{ScliizognathcB.)

8. Charadriomorphce (The Plovers).

9. Cecomorphce (The Gulls).

10. Spheniscomorphce {The Penguins).

11. Geranomorphce (The Cranes).

12. Turnicimorpjhce (The Hemipods).

13. AlectoYomorphce (The Fowls).

14. PteroclomorphcB (The Sand-grouse),

15. Peristeromorphce (The Pigeons).
IG. Heteromorphce (The Hoazin).

ii. The vomer truncated in front.

{JEgithogn aihce. )
lY. Coracomorphce (The Passerines).

18. Cypselomorphce (The Swifts).

19. Celeomorphce (The Woodpeckers).

j8. The Maxillo-palatines united.

{DesmognaiJi<B. )

20. Aetomorphce (The Birds of Prey).

21. PsittacomorphcB (The Parrots).

22. Coccygomorphce (The Cuckoos, King-

fishers, Trogons).

23. Chenomorphce (The Anserine Birds).

24. AmpMmorphce (The Flamingoes).

25. Fdargomorphce (The Storks).

26. Dysporomorphce (The Cormorants).f

* With the exception of DicliolopJius and some species of Crax.
t The subjoined Table, which shows with which of the above groups the
i)ld orders of Birds correspond, may be useful to the student :

/. — ACCIPITBES )

or > . . . . := Aetomorphce.
Raptores )
n. — ScANsoREs =Psittacomo7p7ice, Cotcygomorphoi (in part),

"-'* P-A-SSERE3 I ^J QoracomorpTioe^ CypselomorpTice^ Celeomor-

■j. °^ i" ***'"" 1 phce^ CoccycjomorpTix (in part).

xV. — Galling (with Columb^) =Alectoromo7plim^ PeristeromorplicB, Pterodo-

morpJice,^ lurnicimorplice.

F.— CuRsoREs =Fatitce.

VJ, — GRALLJa ^GharadriomorpTioe^ Geranomorp7c<z, Amphi-

morplice^ PelargomorpJiOB.

yjj, — Palmipedes . . , i =Cecomorplice^ SplieniscomorpTicE^ Chenomor-

phoe^ Dysporomorplice,,

THE FEATHERS OF BIRDS. 235

The exoskeleton of Birds consists almost entirely of epi-
dermic structures in the form of horny sheaths, scales, plates,
or feathers. No bird possesses dermal ossifications, unless the
spurs which are developed upon the legs and wings of some
species may be regarded as such.

The feathers are of various kinds. Those which exhibit
the most complicated structure are called pennoe, or contour
feathers^ because they lie on the surface and determine the
contour of the body. In every penna the following parts are
to be distinguished : A main stem {scajms) forming the axis
of the feather, and divided into a proximal hollow cylinder,
partly imbedded in a sac of the derm, called the calamus^ or
quill ; and a distal vexillitm^ or vane, consisting of a four-sided
solid shaft, the rachis, which extends to the extremity of the
feather, and bears a number of lateral processes, the harhs.
The calamus has an inferior aperture {umbilicus mferio7-),m.io
which the vascular pulp penetrates ; and a superior aperture
{iDnhilicus sujyerior) situated on the under-surface of the
feather at the junction of the calamus with the scapus. The
barbs are narrow plates, tapering to points at their free ends,
and attached by their bases on each side of the rachis. The
edges of these barbs are directed upward and downward,
when the vexillum of the feather is horizontal. The inter-
stices between the barbs are filled up by the harhules; pointed
processes, which stand in the same relation to the barbs, as
the barbs do to the rachis. The barbules themselves may be
laterally serrated and terminated by little hooks, which inter-
lock with the hooks of the opposed barbules. In very many
birds each quill bears two vexilla; the second, called the
aftershaft [lujporachis) being attached on the under side of
the first close to the superior umbilicus. The aftershaft is
generally much smaller than the chief vexillum ; but in some
birds, as the Casuaridce^ the two are of equal size, or nearly
so. Muscles pass from the adjacent integument to the feather
sac, and by their contraction erect the feather. The other
kinds of feathers differ from the pennge, in ha^dng the barbs
soft and free from one another, when they constitute pernio-
pluiTKB^ or plumulm (down), according as the scapus is much
or little developed. When the scapus is very long, and the
vexillum very small or rudimentary, the feather is termed a
Jilopluina.

The contour feathers are distributed evenly over the body
only in a few birds, as the Hatitce^ the Penguins, and some
others. Generally, the pennse are aiTanged in definitely cir-

236 THE ANATOMY OF VERTEBRATED ANIMALS.

cumscribed patches or bands, between which the integument
is either bare, or covered only with down. These series of
contour feathers are termed ^:>^e?'y/c€^, and their interspaces,
apteria.

In some birds, such as the Herons, plumulas of a peculiar
kind, the summits of which break off into a fine dust, or pow-
der, us fast as they are formed, are develo23ed upon certain
portions of the integument, which are termed powder doion
patches.

The integument of birds is, for the most part, devoid of
glands; but many birds have a peculiar sebaceous gland
developed in the integument which covers the coccyx. This
uropygicd gland secretes an oily fluid, Avhich the bird spreads
over its feathers by the operation of "preening." The excre-
tion passes out by one or two apertures, commonly situated
upon an elevation, which may or may not be provided with a
special circlet of feathers.

In various birds (e. g., the Turkey) the integument about
the head and neck develops highlj^-vascular and sometimes
erectile processes {comhs^ wattles).

The spinal column of birds contains numerous and well-
ossified vertebrae, a considerable number of which (more than
six) are anchylosed together to form a sacrum. Of the verte-
brae which enter into the composition of this complex bone,
however, not more than from three to five can be regarded as
the homologues of the sacral vertebrjB of a Crocodilian or
Lacertilian reptile. The rest are borrowed, in front, from the
lumbar and dorsal regions ; behind, from the tail. The cervi-
cal region of the spine is always long, and its vertebrae, which
are never fewer than eight, and may be as many as twenty-
three, are, for the most part, large in proportion to those of
the rest of the hody.

The atlas is a relatively small ring-like bone; and the
transverse ligament may become ossified and divide its aper-
ture into two — an upper, for the spinal cord, and a lower for the
odontoid process of the axis vertebra. The os odontoidewn
is always anchjdosed with the second vertebra, and constitutes
a peg-like odontoid process.

The spines of the succeeding cervical vertebrae are often
obsolete, and are never very prominent in the middle region
of the neck. The anterior faces of their elongated vertebral
centra are cylindroidal, slightly excavated from above down-
ward, and convex from side to side ; while the posterior faces

THE VERTEBRA IN BIRDS. 237

are convex from above downward, and concave from side to
side. Hence, in vertical section, the centra appear procoelous ;
in horizontal section, opisthocoelous ; and this structure is ex-
ceedingly characteristic of birds. The under surfaces of the
centra frequently give off median inferior processes. In the
Matitce, it is obvious that the cervical vertebrse have short
transverse processes and ribs, disposed very much as in the
Crocodilia. For, in young birds, the anterior end of the lat-
eral face of each vertebra bears two small processes, an upper
and a lower ; and the expanded head of a styliform rib is ar-
ticulated w^ith these by two facets which represent the capitu-
lum and the tuberculum. With age, the cervical ribs may
become completely anchylosed; and then they appear like
transverse processes, perforated at the base by a canal, which,
as in the Crocodilia^ contains the vertebral artery and vein,
and the main trunk of the sympathetic nerve. The cervical
ribs and transverse processes are similarly disposed in very
young Carinatce^' but in these birds their form frequently be-
comes much modified in the adult ; and they develop pro-
longations, which extend downward and inward, and protect
the carotid artery or arteries.

The neural arches have well-developed pre- and post-
zygapophyses. The ribs of one or two of the posterior cervi-
cal vertebrse become elongated and freely movable in the
CarinatCB^ as in the JRatitoe.

The first dorsal vertebra is defined as such, by the union
of its ribs with the sternum by means of a sternal rib ; which
not only, as in the Crocodilia, becomes articulated with the
vertebral rib, but is converted into complete bone, and is con-
nected by a true articulation with the margin of the sternum.

The number of the dorsal vertebriB (reckoning under that
head all the vertebrae, after the first dorsal, which possess dis-
tinct ribs, whether they be fixed or free) varies. The centra
of the dorsal vertebrae either possess cylindroidal articular
faces, like those of the neck, as is usually the case ; or, more or
fewer of them may have these faces spheroidal, as in the Pen-
guins. In this case, the convex face is anterior, the concave,
posterior. They may, or may not, develop inferior median pro-
cesses. They usually possess well-marked spinous processes.
Sometimes they are slightly movable upon one another ; some-
times they become anchylosed together into a solid mass.

It is characteristic of the dorsal vertebrae of Birds that the
posterior, no less than the anterior, vertebrae present a facet,
or small process, on the body, or the lower part of the arch,

238

THE ANATOMY OF VERTEBRATED ANIMALS.

of the vertebra for the capitulum of the rib, while the upper
part of the neural arch gives off a more elongated transverse
process for the tuberculum. Thus the transverse processes of
all the dorsal vertebrae of a bird resemble those of the two an-
terior dorsals of a crocodile, and no part of the vertebral col-
umn of a bird presents transverse processes with a step for
head of the rib, like those of the great majority of the vertebrae
of Crocodllia, Dlnosauria^ Dicynodontia^ and JPterosauria.

The discrimination of the proper lumbar, sacral, and ante-
rior caudal vertebrae, in the anchvlosed mass which constitutes
the so-called " sacrum " of a bird, is a matter of considerable

Pig. 80. — ^The "Sacrum" of a Chick, dl., dorso-lumhar ; s., sacral; c, caudal vertebrsE,.

difficulty. The general arrangement is as follows : The most
anterior lumbar vertebra has a broad transverse process, which
corresponds in form and position with the tubercular trans-
verse process of the last dorsal. In the succeeding lumbar
vertebrae tliis process extends downward ; and, in the hinder-
most, it is continued from the centrum, as well as from the
arch of the vertebra, and forms a broad mass which abuts
against the ilium.* This process might well be taken for a
sacral rib, and its vertebra for the proper sacral vertebra.
But, in the first place, I find no distinct ossification in it ; and,
secondly, the nerves which issue from the intervertebral fora-
mina in front of and behind this vertebra enter into the lum-
bar plexus, which gives origin to the crural and obturator
nerves, and not into the sacral plexus, which is the product of
the nerves which issue from the intervertebral foramina of the
proper sacral vertebrae in other Vertehrata. Behind the last
lumbar vertebra follow, at most, five vertebrae, which have no
ribs, but their arches give off horizontal, lamellar, transverse
processes, which unite with the ilia. The nerves which issue
from the intervertebral foramina of these vertebra3 unite to

* It would be more proper to say that ossification extends into it from tho
centrum as well as from the neural arch. The process, like other processes,
exists before the centrum is dilferentiated from the arch by ossification.

THE YERTEBRJE IN BIRDS. 239

form the sacral plexus, whence the great sciatic nerve is given
off; and I take them to be the homologues of the sacral ver-
tebrae of Heptilia. The deep fossa; between the centra of these
vertebras, their transverse processes, and the ilia, are occujDied
by the middle lobes of the kidneys.

If these be the true sacral vertebras, it follows that their
successors are aijtterior caudal. They have expanded upper
transverse processes, like the proper sacral vertebras ; but, in
addition, three or four of the most anterior of these vertebrce
possess ribs which, like the proper sacral ribs of reptiles, are
suturally united, or anchylosed, proximally, with both the
neural arches and the centra of their vertebriB, while, distally,
they expand and abut against the ilium. The anchylosed
caudal vertebrse may be distinguished as urosacral. The
caudal vertebrae which succeed these may be numerous and all
distinct from one another, as in Arclimopteryx and Rhea ; but,
more generall}-, only the anterior caudal vertebrae are distinct
and movable, the rest being anchylosed into a plough-share
shaped bone, or pygostyle^ which supjDorts the tail-feathers
and the uropygial gland, and sometimes, as in the Wood-
peckers and many other birds, expands below into a broad
polygonal disk.

The centra of the movable presacral vertebras of Birds
are connected together by fibro-cartilaginous rings, which
extend from the circumference of one to that of the next.
Each ring is continued inward into a disk with free anterior
and posterior faces — the meniscus. The meniscus thins tow-
ard its centre, which is always perforated. The synovial
space between any two centra is, therefore, divided by the
meniscus into two very narrow chambers, which communicate
by the aperture of the meniscus. Sometimes the meniscus is
reduced to a rudiment ; while, in other cases, it may be united,
more or less extensively, with the faces of the centra of the
vertebrae. In the caudal region, the union is complete, and
the meniscus altogether resembles an ordinary intervertebral
cartilaofe.

A ligament traverses the centre of the aperture in the
meniscus ; and, in the chick, contains the intervertebral por-
tion of the notochord. As Jitger * has shown, it is the homo-
logue of the odontoid ligament in the cranio-spinal articula-
tion ; and of the pulpy central part of the intervertebral fibro-
cartilages in 3fa77imaUa,

*"Da9 "Wirbclkorpergelenk der Vogel." SitzungsLericlite der Wiener
Akademie, 1858.

240 THE ANATOMY OF VERTEBRATED ANIMALS.

All the vertebral ribs m the dorsal region, excej)t, perhaps,
the very last free ribs, have widelj-separated capitula and
tubercula. More or fewer have well-ossified uncinate processes
attached to their posterior margins, as in the Crocodilia,
The vertebral ribs are completely ossified up to their junction
with the sternal ribs. The sternum, in birds, is a broad plate
of cartilage, which is always more or less completely I'eplaced
in the adult by membrane-bone.* It begins to ossify' by, at
fewest, two centres, one on each side, as in the Hatitce. In
the Carinatce it usually begins to ossify by five centres, of
which one is median for the keel, and two are in pairs, for the
lateral parts of the sternum. Thus the sternum of a chicken
is at one time separable into five distinct bones, of which the
central keel-bearing ossification (r. to on. x. in Fig. 81) is termed
the lophosteon^ the antero-lateral piece which articulates with
the ribs, ^9^ewro5?eo?^ (79/. o.), and the posterolateral bifurcated
piece, metosteon.

Though the sternum, in most birds, seems to differ very
much in form from that of the JReptiUa^ it is rhomboidal in
the Casuaridce^ where it diflers from the reptilian sternum
chiefly in the greater proportional length of its posterior sides,
the absence of median backward prolongations, and the con«
vexity of its ventral surface. But in other birds, and notably
in many Carinatoe^ the antero-lateral edges, which are grooved
to receive the coracoids, form a much more open