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ANATOMY OF VERTEBRATED
ANIMALS.

BY

THOMAS H. HUXLEY, LL.D., F.RBS.,

AUTHOR OF ‘*“‘LAY SERMONS,” ‘‘MAN’S PLACE IN NATURE,”’ ‘‘ ORIGIN OF SPECIES,”
ELC; ELC.

NEW YORE:
eae PLETON AND. COMPANY,
1, 8, AnD 5 BOND STREET.
1886.

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Pita: vO a

Pan Ee AC: lic

TuE 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 hold 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, Carus, Dugés, Flower, Gegenbaur,
Hyrtl, Von Meyer, Miller, 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
Gegenbaur.

Lonpor, September, 1871.

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

*

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CON TENTS:

Cuap I.—A GrneERAL VIEW OF THE ORGANIZATION OF THE VERTEBRATA—
THE VERTEBRATE SKELETON, . : : : :

IJ.—Tue Mvscies AND THE VISCERA—A GENERAL VIEW OF THE

PAGH

~T

ORGANIZATION OF THE VERTEBRATA, . ; . : . 44

Ti].—Tue Provinces oF THE VERTEBRATA—THE Ciass Pisces, . 100
IV.—Tue Ciass AMPHIBIA, . é ; ‘ : : ; . 149
Y.—THE CLASSIFICATION AND THE OSTEOLOGY OF THE REpTILIA, . 167
VI.—TuHE CLASSIFICATION AND THE OsTEOLOGY oF Birps, . . 238
VII.—TuHE MuscLes AND THE VISCERA OF THE SAUROPSIDA, . . 256
Vill.—Tae CLASSIFICATION AND ORGANIZATION OF THE MamMatta, . 278

uf ea yy )
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THE ANATOMY

oF

VERTEBRATED ANIMALS.

CHAPTER I.

4 GENERAL VIEW OF THE ORGANIZATION OF THE VERTE-
BRATA-——THE VERTEBRATE SKELETON.

The Distinctive Characters of the Vertebrata.—The Verte-
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-spinal
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
the development and union of outgrowths of the blastoderm,
which are not formed in the Jnvertebrata.*

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

* It is possible that an exception to this rule may be found in the Ascid-
ians. The tails of the larve 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 Amphioxus.

B THE ANATOMY OF VERTEBRATED ANIMALS.

ceral tubes, certain structures, which 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 Vertebrata; 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 Vertebrata, 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, temporarily or permanently, in communication
with the exterior. Nothing corresponding with these arches
and clefts is known in the Jnvertebrata.

A vertebrated animal may be devoid of articulated limbs,
and it never possesses more than two pairs. These are always
provided 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 m 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
with the exterior—recalling, in the latter case, the atrial cavi-
ties of Mollusca.

In all Vertebrata, except Amphioxus, there is a single
valvular heart, and all possess an hepatic portal system ; the
blood of the alimentary canal never being wholly 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 VERTEBRATA. 9

The Development of the Vertebrata.—The ova of Verte-
brata have the same primary composition as those of other
animals, consisting of a germinal vesicle, containing one or
many germinal spots, 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.

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Fic. 1.—Diagrammatie section of the pregnant uterus of a decidnate placental mammal
(Homo): u, uterus; 2, Fallopian tube; c, neck of the uterus; du, uterine decidua; da,
decidua serotina; dr, decidua reflera; 2,2,’ villi; ch, chorion; @ amnion; 76,
umbilical vesicle; a, allantois.

Impregnation may take place, either subsequently to the
extrusion of the egg, when, of course, the whole development
of the young goes on outside the body of the oviparous
parent; or it may occur before the extrusion of the egg. In
the latter case, the development of the egg in the interior of
the bedy may go no further than the formation of a patch of
primary tissue; as in birds, where the so-called cicatricula, or
“tread,” which is observable in the new-laid egg, is of this
nature. Or, the development of the young may be 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 ovoviviparous. Or, the young
may receive nourishment from its viviparous parent, before
birth, by the 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 placenta, 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 repiaced 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 mi/k, 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-masses, 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 cleavagé-masses eventually be-
come very small, and are called embryo-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 (hypoblast), which gives
rise to the epithelium of the alimentary tract; and an outer,
the serous stratum (epiblast), from which the epidermis and
the cerebro-spinal nervous centres are evolved. 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

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12 THE ANATOMY OF VERTEBRATED ANIMALS.

the substance of the mesoblast along each side of this groove
grows up, carrying with it the superjacent epiblast. Thus are
produced the two dorsal lamine, 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 lines this, cut off from the rest,
becomes thickened, and takes on the structure of the brain, or
Encephaion, 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 laminz forms the ventral lamine ; 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 laminz 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 ina kind of bag. This bag is the
first-formed and the most constant of the temporary, or foetal,
appendages of the young vertebrate, the wmbilical vesicle.

While 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 two lamelle@. One of these, the visceral
lamella, remains closely adherent to the hypoblast, forming
with it the splanchnopleure, and eventually becomes the proper
wall of the enteric canal ; while the other, the parietal lamella,
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 wmbilicus.

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

The Fetal Appendages of the Vertebrata—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, posterior:y, and laterally, over the body
of the embryo. The free margins of this fold gradually ap-
proack one another, and, ultimately uniting, the inner layer
of the fold becomes converted into a sac filled with a clear

THE FETAL APPENDAGES. 13

fluid, the Amnion ; while the outer layer either disappears or
coalesces with the vitelline membrane, to form the Chorion
(Fig. 3\.

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Fic. 8.—Later stages of the development of the body of a Fowl than those represented in
Fig. 2.—E, embryo at the third day of incubation; g, heart; h, eye; 7, ear; %, visceral
arches and clefts ; 7, m, anterior and posterior folds of the amnion which have not yet
united over the body; 1, 2, 3, first, second, and third cerebral vesicles; 1a, vesicle of the
third ventricle—F, embryo at the fifth day of incubation. The letters as before, except
m, 0, rudiments of the anterior and posterior extremities; Am, amnion; Ad/ (the allan-
tois, hanging down from its pedicle); Um, umbilical vesicle-—G, under-view of the head
of the foregoing, the first visceral arch 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
single or double outgrowth from the under surface of the meso-

14 THE ANATOMY OF VERTEBRATED ANIMALS.

blast, behind the alimentary tract; but soon takes the form
of a vesicle, and receives the ducts of the primordial kidneys,
or Wolffian bodies. It is supplied with blood by two arteries,
called hypogastric, which spring from the aorta; and it varies
very much in its development. It may become so large as to
invest all the rest of the embryo, in the respiratory, or nutri-
tive, processes of which it then takes an important share.

The splitting of the ventral laminz, 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 Amphibia 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 egg 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 wrachus, 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
Amphibia remain open throughout life; and the visceral
arches of all fishes (except Amphioxus), and of all Amphibia,
throw out filamentous or lamellar processes, which receive
branches from the aortic arches, and, as branchiw, subserve
respiration. In other Vertebrata all the visceral clefts become
closed and, with the frequent exception of the first, obliterated ;
and no branchiz 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
exoskeleton, or endoskeleton.

The Vertebrate Endoskeleton.—This consists of connective
tissue, to which 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 endoskeleton usually consists of two systems of

THE VERTEBRATE ENDOSKELETON. 15

skeletal parts, the spinal 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 lamin 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 anterior 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 hinder enlargement, or
the posterior cerebral vesicle, behind that extremity (Fig. 4, D
and Ek). 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 indifferent
tissues which ensheath the notochord passing without 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 effected by the appearance of the proto-
vertebree. At regular intervals, commencing at the anterior
part of the cervical region, and gradually extending backward,
the indifferent 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).
Kach 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 protovertebra.

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

16 THE ANATOMY OF VERTEBRATED ANIMALS.

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

ha. 4.—Successive stages of the development of the 4ead of a Chick. I, II, III, first, see-
ond, and third cerebral vesicles; Za, vesicle of the cerebral hemisphere; Jd, vesicle of
the third ventricle; a, rudiments of the eyes and optic nerves; 0, of the ears; g. of the
olfactory organs; d, the infundibulum; e, the pineal gland; ¢c, protovertebre; A, noto-
chord; 1, 2, 3, 4, 5, visceral arches; V, VII, VIII, the trigeminal, portio dura, and ninth
and tenth pairs of cranial nerves; %, the nasal process; /, the maxillary process; @, the
first visceral cleft. A,B, upper and under views of the head of a Chick at the end of
the second day. ©, side-view at the third day. D, side-view at seventy-five hours.
side-view of the head of a Chick at the fifth day, which has been subjected to slight press-
ure. F, head of a Chick at the sixth day, viewed from below.

OSSIFICATION OF THE VERTEBRA. 17

The Spinal System.—The protovertebre 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—tfrom its superficial layer, a segment of the
dorsal muscles, are produced.

Chondrification extends upward into the walls of the dorsal
tube, to produce the newral arch and spine 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 vertebre are
usually ossified, in great measure, from ringlike deposits which
closely 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, with or without 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 vertebre
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.

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

18 THE ANATOMY OF VERTEBRATED ANIMALS.

In the Mammalia, the centra of the vertebre 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 vertebree may be united together by
synovial joints, or by ligamentous fibres—the intervertebral
ligaments. The arches are connected by ligaments, and gen-
erally, in addition, by overlapping articular processes called
zygapophyses, or oblique processes,

In a great many Vertebrata, the first and second cervical,
or atlas and axis, vertebre 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 odontoideum, or anchylosing with the body
of the axis, and becoming the so-called odontoid process of
this vertebra.

In Vertebrata with well-developed hind-limbs, one or more
vertebra, 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-
tebre are artificially classed as cervical, dorsal, and lumbar.
The 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. Vertebrz without distinct ribs,
between the last dorsal and the sacrum, are Zumbar, . Ver-
tebre, with or without ribs, in front of the first dorsal are
cervical,

The vertebrae which lie behind the sacrum are caudal or
coecygeal, Very frequently, downward processes of these
vertebra enclose the backward continuation of the aorta, and
may be separately ossified as swbcaudal, 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 (C),
united with which by the newrocentrai suture is the neural
urch, which rises into the neural spine (VN. 8.). Two pro-
cesses, the prezygapophyses (Z), extend from the front part of
the arch, and have flat 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 postzygapophyses (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

eessor or successor in the series. The transverse processes are
two on each side, one superior and one inferior, ‘The former
(Zt) articulates with the ¢uberculum of the rib, the latter
( Cp.t) with its eapitulum. They may, therefore, be called ca-
pitular and tubcrewlar transverse processes respectively. Hach

SE SEY

Fic. 5.—A segment of the endoskeleton in the anterior thoracic region of the body of a croc-
odile.—0, the centrum or body of the vertebra; N.S. the neural spine; Z, the prezy-
gapophysis; 7, the postzygapophysis; 7.t, the transverse process which articulates
with the tuberculum of the rib (¢); Cp.¢, that which articulates with the capitulum of
the rib (Cp); V.7, the ossified vertebral rib; V.7’, the part of the vertebral rib which
remains cartilaginous; Sé.r, the sternal rib; S¢, an artificially-separated segment of the
sternum ; ?.u, the uncinate process.

rib is divided by an articulation into a vertebral ( V.r) and a
sternal (St.7) part. The former remains unossified for a con-
siderable distance at its distal end ( V.r’); 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 (S¢).
A cartilaginous, or partly ossified, uncinate process (P.u.) 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 Vertebrata, the caudal vertebrae
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-vertebre, 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-

THE ANATOMY OF VERTEBRATED ANIMALS.

20

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Band. ©
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retains the same direction as the

of a fish, it occasionally

so as to form

trunk part, but is far more generally bent up,

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AN

THE CRANIAL SKELETON. © 21

an obtuse angle with the latter. 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 diphycercal (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 hypwral 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 homocereal fish,
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, Perch, 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 wurostyle.

Fie. 7.—The cartilaginous cranium of a Fow] at the sixth day of incubation, viewed from be-
low.—P, the pituitary space; tr, the trabecule, uniting in front, in the bifurcated eth-
movomerine plate; Qu, the quadrate cartilage; Sc, the semicircular canals; Co, the
cochlea; i, the notochord imbedded in the basilar plate.

The Cranial System.—As has been stated, no protover-
tebrz appear on the floor of the skull; nor is there any cra-
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 VERTEBRATED 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 trabecule cranii. In
front of the fossa, the trabeculz 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 may be devel-
oped in the more anterior parts of the skull do not ordinarily
reach its roof, but leave a wide, 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 turbinals.

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

THE CRANIAL SKELETON. 23

The first visceral arch bounds the cavity of the mouth be-
hind, and marks the position of the mandible or lower jaw.
The cartilage which it contains is termed Meckel’s cartilage.

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

a
iw

4
Wy
NUH)
NTT ih
Hit
WIN TIIE
tit I
1 |
fn

Fic. 8.—Under-v:ew of the head of a Fow] at the seventh day of incubation.—Ja, the cere
bral hemispheres causing the integument to bulge; a, the eyes; g, the olfactory sacs
k, the fronto-nasal process; 7, the maxillary process; 1, 2, the first and second viscer
arches; @, 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 (Vig. 4, F; Fig. 8, 7), bounds the mouth on
each side, and is called the mawillary 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 a fronto-nasai process (Fig. 4, F; Fig. 8, 4).
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 VERTEBRATED 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-
pterygoid 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
Vertebrata, 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.—W hen 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 basi-
occipital bone; that which takes place in the floor of the pitu-
itary fossa becomes the basisphenoid ; 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 swpra-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 may
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
vrbitosphenoidal ossifications may appear and unite below
with the presphenoid.

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

THE TYPICAL BONY SKULL. 25

segments of which the basisphenoid and presphenoid form the
basal parts, are membrane bones, and are disposed in twa
pairs. The posterior are the parietals, the anterior the fron-
tals ; and the segments which they complete are respectively

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26 THE ANATOMY OF VERTEBRATED ANIMAIS.

called parietal and frontal. Thus the walls of the cranial cav-
ity in the typical ossified skull are divisible into three segments
—I. Occipital, 11. Parietal, II]. 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., I1., V., and x.), in the manner shown in the
diagram * on the preceding page.

The cartilaginous cases of the organs of hearing, or the
periotic 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 ossif-
cations of its own. ‘The one in front is the prodtic ; 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.
These three ossifications may coalesce into one, as when they
constitute the petrosal and mastoid 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 prodtic distinct. The prodtic 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, pterotic ossification, is added to the three
already mentioned. It lies on the upper and outer part of the
ear-capsule between the prodtic and the epiotic (see the fig-
ure of the cartilaginous cranium of the Pike, infrd). Bax

In some Vertebrata the base of the skull exhibits a long
and distinct splint-like membrane bone t—the parasphenoid,

* The names of the purely membrane bones in this diagram are in large
eapitals, as PARIETAL; while those of the bones which are preformed in
cartilage are in smaller type, as BAsIsPHENOID.

+ Bones may be formed in two ways. They may be 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 ossifie deposit may take place, from the
first, in indifferent, or rudimentary connective, tissue. In this case the bone
is not prefigured by cartilage. In the skulls of Elasmobranch fishes, and in
the sternum and epicoracoid of Lizards, the bony matter is simply ossified ear-
tilage, or cartilage bone. The parietal or frontal bones, on the other hand,
= always devoid of cartilaginous rudiments, or, in other words, are membrane

Ones.

In the higher Vertebrata the cartilage bones rarely, if ever, remain as such 3
but the primitive ossified cartilage becomes, in great measure, absorbed an
replaced by membrane bone, derived from the perichondrium.

THE BONES OF THE FACE. 27

which underlies it from the basi-occipital to the pre-sphenoidal
region. In ordinary fishes and Amphibia, this bone appears
to replace the basisphenoid and presphenoid functionally,
while in the higher Vertebrata 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
bone may be developed in the prefrontal region of the nasal
capsule, and bound the exit of, the olfactory nerve externally.

A postfrontal bone may appear behind the orbit above the
alisphenoid. Sometimes it seems to be a mere dismember-
ment of that bone; but,in 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 sguamosal, 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.

The Osseous Facial Apparatus.—The 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 premazille 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 ap-
pearance in the same process. The chief of these is the maa-
lla, which commonly unites, in front, with the premaxilla.
Behind the maxilla there may be a second, the jugal ; and
occasionally behind this les a third, the guadratozjugal.

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-orbital and post-orbital ossifications
inay be connected with the bony boundaries of the orbit.

When these and the postfrontal membrane bone are si-
multaneously developed, they 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 guadrate
bone, or mandibular suspensorium. 'The lower series (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 JIchthy-
osauria, Chelonia, Crocodilia, and some Lacertilia, exhibit
this double series of bones most completely.

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 the 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 with 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 poste-
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 qguadrate bone found
in most vertebrates, the malleus 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
time, but does not ossify. It becomes surrounded by bone,
arising from one or several centres, in the adjacent membrane,
and the ramus of the mandible 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 Vertebrata. In birds and reptiles,

U
MN

Ds

\ “Oi

TH Ili, ZI

N ~ IN ri

‘a el \ Ran Ques
{pu Ss SS fy
ae 3

ante
caine

Fig. 9.—The head of a fetal Lamb dissected so as to show Meckel’s cartilage, J/; the
malleus, m,; the incus, 7; the tympanic, 77; the hyoid, 7; the squamosal, Sq;
pterygoid, P¢; palatine, p2; lachrymal, Z; premaxilla, yma; nasalsac, V; Eustachian
tube, Hu.

the proximal end of the quadrate bone articulates directly
(with a merely apparent exception in Ophidia), and indepen-
dently 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 hyomandibular, which 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,
ealled columella auris, or stapes, the inner end of which, in
the higner Vertebrata, 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 VERTEBRATED ANIMALS.

chial clefts; within this is developed a series of raylike mem-
brane bones, termed opercular and branchiostegal, which be-
come closely connected with the hyoidean arch. A corre-
sponding process of the skin is developed in the Batrachian
Tadpole, and grows backward over the branchix. 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.

a The branchial skeleton bears
the same relation to the posterior
visceral arches that the hyoidean
Eth! does to the second. When fully
/ developed, it exhibits ossified lat-
} | eral arches, connected by median
Pr pieces, and, frequently, provided
I with radiating appendages which
give support to the branchial mu-
cous membrane. It is only found
in those Vertebrata which breathe
by gills—the classes Pisces 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
Cetacea, the bones about the re-
gion of the nose are unequally
developed, and the skull becomes
asymmetrical, In the Flatfishes
(Pleuronectide), the skull be-
Fic. 10.—The skull of a Plaice ( Platessa wertcaeees completely distorted, that

vulgaris), viewed from above. The the two eyes lie on one side of
dotted line a, b, is the true morpho- the body, which is, in Some cases
logical median line; Or, Or, the po- J? : ? : ’
sition of the two eyes in their orbits; the left, and, in others, the right
doth, cthinold 5, Pry, prefrontal: be side. In certain of these fishes,
parictal; SO, supra-occipital; #p.0, the rest of the skull and facial
epiotic. .
bones, the spine, and even the
limbs, partake in this asymmetry. The base of the skull and

THE CARPUS AND THE TARSUS. 3i

its occipital region are comparatively little affected ; but, in the
interorbital region, the frontal bones and the subjacent carti-.
iaginous, 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 brachium in the fore-limbs, femur in the hind; the
middle is antebrachium, or crus; the distal is manus, or pes.
Hach of these divisions has its proper skeleton, composed of
cartilage and bone. The proximal division, normally, con-
tains only one bone, os humert, or humerus, in the brachium,
and os femoris, or 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. Hach
digit has a proximal basi-digital (metacarpal or metatarsal)
bone, upon which follows a linear series of phalanges. It is
convenient always to count the digits in the same way, com-
mencing 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, ili, 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 inarrangement. 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 severai metacar-
pal or metatarsal bones; while, on its proximal side, are
three bones—one radiale or tibiale, articulating with the radi-
us or tibia; one wlnare or fibulare, with the ulna or fibula;
and one intermedium, 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,

:
i}
.

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

Proximal carpa! bones: 7, radiale; 2, intermedium; w, ulnare; the centrale is the middle
unlettered bone.

Proximal tarsal bones; #, tibiale; 7, intermedium; /, fibulare; ¢, centrale; 1, 2,8,4,8
distal carpalia and tarsalia; 1, 11, In, IV, V, digits.

commonly, the typical arrangement is disturbed by the sup-
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 ulnaris,
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 wnciforme. 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 eudboides.

The Position of the Limbs.—In their primitive position,
the limbs are straight, and are directed outward, at right
angles to the axis of the body; but, as development proceeds,
they become bent in sucha 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
division. Thus the ventral aspects of the antebrachium and
erus come to look inwardly, and the dorsal aspects outwardly ;
while the ventral aspects of the manus and pes 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 antebrachium, 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 twec
pre-axial, or radial, or tibial digits; and two post-axial, ot
ulnar, or fibular digits, in each limb. The most anterior of the
digits (i) is called pollex, in the manus; and Aallux in the pes.
The second digit (ii) is the index; the third (iii) the medius ;
the fourth (iv) the annelaris ; and the fifth (v) the minimus.

In many Amphibia and Reptilia, 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 brachium is turned backward and the
thigh 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.

34 THE ANATOMY OF VERTEBRATED ANIMAIS.

_ In Bats, a line drawn from the acetabulum 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
the excess, or defect, in the development of particular digits,
and from the manner in which the digits are connected wita
one another, and with the carpus or tarsus. In the Lcehthyo-
sauria and Plesiosauria, the Turtles, the Cetacea 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 Péerosauria, and the
four ulnar digits in the 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 digits themselves are enclosed in a common integu-
mentary sheath; the third invariably, and the second usually,
is devoid of aclaw. 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.

Among terrestrial mammals, the most striking changes 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 (Rhinoceros), two (most Ruminantia), or
one (Liyuide).

i

The Pectoral and Pelvic Arches.—The proximal skeletal
elements of each pair of limbs (humert or femora) are sup-
ported by a primitively cartilaginous, pectoral, or. pelvic
girdle, which lies external to the costal elements of the verte-
bral skeleton. This girdle may consist of a simple cartilagi-
nous are (as in the Sharks and Rays), or it may be complicated
by subdivisions and additions.

The pectoral arch may be connected with the 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-
bree by the intermediation of ribs. At first, it consists of one

THE PECTORAL ARCH. 35

continuous cartilage, on each side of the body, 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 differences in the mode of ossification of the various
parts, and by other changes, that region of the primitively

Fic. 12.—Side-view of the pectoral arch and sternum of a Lizard (guana tuberculata).—-
Sc, scapula; s.sc, supra-scapula; e7, coracoid; g/, glenoidal cavity; S¢, sternum; «.st,
xiphisternum; 72.sc, mesoscapula; p.cr, precoracoid; m.c7, mesocoracoid; ¢€.c7’, epi-
coracoid ; ¢/, clavicle; z.cl, interclavicle.

cartilaginous pectoral arch which lies above the glenoidal
cavity may be ultimately divided into a scapula and a supra-
scapula ; while 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 Vertebrata 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 scapula
and coracoid, but takes no part in the formation of the
glenoid cavity, and is usually, if not always, a membrane
bone. In many Vertebrata, the inner ends of the clavicles

36 THE ANATOMY OF VERTEBRATED ANIMALS.

are connected with, and supported by, a median membrane
bone which is closely connected with the ventral face of the
sternum. This is the interclavicula, frequently called epister-
num

FL SC,

Fic. 13.—-Ventral view of the sternum and pectoral arches of Jguana tuberculata. 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 Vertebrata
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-
tilaze—one in the dorsal, and two in the ventral, moiety.
Hence, the pelvic arch eventually consists of a dorsal portion,
called the iliuwm, and of two ventral elements, the pubis ante-
riorly, and the zschiwm posteriorly. All these generally enter
into the composition of the acetabulum.

The ilium corresponds with the scapula. In the higher
Vertebrata the outer surface of the latter bone becomes di-
vided by a ridge into two fossz. The ridge, called the spine
of the scapula, frequently ends in a prominent process termed
the acromion, and with this, in Mammalia, the clavicle artic
ulates, In like manner, the outer surface of the ilium be:-

THE PELVIC ARCH. 39

zomes divided by a ridge which 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 the epicoracoid.

The pelvis possesses no osseous element corresponding
with the clavicle, but a strong ligament, the so-called Pow
part’s ligament, stretches from the ilium to the pubis in many
Vertebrata and takes its place. (Fig. 14, Pp.)

Fie. 14.—Side-view of the left Os innominatum of Man: 77, ilium; Js, ischium 3; P& pubis
A, acetabulum; Pp, Poupart’s ligament.

On the other hand, the marsupial bones 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 same 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 Limbs of Fishes.—The limbs of Fishes have an endo-
skeleton which only imperfectly corresponds with that of the
higher Vertebrates. For while homologues of the cartilagi-

58 THE ANATOMY OF VERTEBRATED ANIMALS.

nous, and even of the bony, constituents of the 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 way,
with the limb-bones, or cartilages, of the other Vertebrata.

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 Elasmobranchii possess three basal
cartilages which articulate with the pectoral arch, and are
called, respectively, from before backward—propterygial, me-
sopterygial, and metapterygial basalia. 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 Klasmobranchii ; but the pro-
pterygial, mesopterygial, and metapterygial basalia, are more
or less ossified, and are succeeded by a series of elongated
redialia, which are also, for the most part, ossified. Beyond

mn

Fte@ 16.---The right pectoral member of the Monkfisn (Squatina): %, propterygiam, ma,
mesopterygium; m/, metapterygium,

THE LIMBS OF FISHES. 39

these follow some small additional radialia, 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 mesopterygial 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 Zeleoste/,
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 hehind 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.) % / 97,

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 swpra-clavicular and 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 under 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 Kzxoskeleton never at-
tains, in vertebrated animals, the functional importance which
it so frequently possesses among the Jnvertebrata, and it va-
ries very greatly in the degree of its development.

The integument consists of two layers—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 cf more or less completely-

40 THE ANATOMY OF VERTEBRATED ANIMALS.

formed connective tissue. An exoskeleton may 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, arez, or processes, of the dermis. When the
latter are overlapping folds, the horny epidermic investment
is called a scale, sguama. 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 or a 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 under
surface, and then spreads out into a flat vane, subdivided into
barbs, barbules, etc., by a further process of splitting of the
primary horny cone.

The epidermis remains soft and delicate in Fishes and
Amphibia. In Reptilia it sometimes takes the form of plates,
which attain a great size in many Chelonia ; sometimes, that
of overlapping scales, as in Ophidia and many Lacertilia ;
but, sometimes, it remains soft, as in some Chelonia and in the
Chameleons. 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 Feptilia. Corni-
fied epidermié 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 with scales, the
Armadillos with plates, and most terrestrial mammals with a
thick 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 papillee of the dermis extend
into it. These papilla, however, are comparable to the ridges
of the bed of the nail, not to the papillze of the hairs.

THE EXOSKELETON. 4]

The dermal exoskeleton arises from the hardening of the
dermis ; in the majority of cases by the deposit of bone-earth,
in more or Jess 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 (Zsor), to show the fins: P, pectoral; V, ventral; A, anal;
C, caudal; D, dorsal, fins. Op., operculum; P.Op., preoperculum ; 67, branchiostegal
rays.—B, scales of the dermal exoskeleton of the same fish.

No dermal exoskeleton (except that of the fin-rays) is found
in the lowest fishes, Amphioxus and the Marsipobranchit. In
most Zeleostei, the integument is raised up into overlapping
folds; and, in these, calcification takes place in laminz, 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 Zéleoste?. 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 petrosa, 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

42 THE ANATOMY OF VERTEBRATED ANIMALS.

in the dorsal region, 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 simple at the base, but become jointed transversely, and
split up longitudinally, toward their extremities (Fig. 6).
Hach fin-ray consists of two nearly equal and similar parts,
_ which cohere by 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 interspinous cartilages, or bones,
which lie between the fin-rays and the superior or inferior
spines of the vertebrze. In the paired fins, they are radial or
basal, cartilaginous or osseous, elements of the endoskeleton.

The Amphibia in general are devoid of dermal exoskeleton,
but the Cecilie have scales like those of fishes. Ceratophrys
has plates of bone developed in the dorsal integument, which
seem to foreshadow the plates of the carapace of the Chelonia;
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 Crocodilia 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 Téleosauria, 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 Chelonia,
and will be particularly described under the head of that order.

In the Mammalia the development of a dermal exoskeleton
is exceptional, and occurs only in the loricated dentata, 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 intezument may be men-
tioned. Integumentary glands do not appear to exist in
Fishes, but they attain an immense development in some of
the Amphibia, as the Frog. Among Septilia, Lizards fre-
quently present such glands in the femoral and cloacal regions ;
and, in Crocodiles, integumentary glands, which secrete a
musky substance, lie beneath the jaw. In Birds they attain a
considerable size in the uropygial gland; and, in Mammalia,
acquire a large development in connection with the sacs of the

THE EXOSKELETON. 43

hairs, or as independent organs, in the 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 ‘listinct
chromatophores, as in the Chameleon.

CHAPTER ff.

THE MUSCLES AND THE VISCERA—A GENERAL VIEW OF THE
ORGANIZATION OF THE VERTEBRATA.

THE muscular system of the Vertebrata 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 Muscular System of the Trunk and Head.—This con-
sists of two portions, which differ fundamentally in their
origin, and in their relations to the endoskeleton. The one
takes its origin in the protovertebre ; each protovertebra be-
coming differentiated, as we have seen, into three parts; a
spinal ganglion 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 only by the endoskeleton of the trunk (or
the vertebre and their prolongations, the ribs), but by the
ventral branches of the spinal nerves.

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

.
a4
:
a
a
,
.
.
4
:

EPISKELETAL AND HYPOSKELETAL MUSCLES. 45

In the lowest Vertebrata—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 vertebre.
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 hyoidean 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 Vertebrata, 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 by the
superior caudal muscles, and by the erector spine ; which, as
it splits up, anteriorly, and becomes attached to the vertebre,
and to the ribs, and to the skull, acquires the names of sp7-
nalis, semispinalis, longissimus dorsi, sacrolumbalis, inter-
transversalis, levatores costarum, complexus, splenius, recti
postici, and recti laterales.

The ventro-lateral division of the fish’s lateral muscle 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 abdominis, extend-
ing from the pelvis to the sternum—the sterno-hyoidet, 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 obliqui externi of the abdomen

stretching from the first rib to the clavicle; the scalent from
the anterior dorsal ribs to the cervical ribs and transverse
processes, and the sterno- and cleido-mastoidei from the ster-
num and clavicle to the skull.

The fibres of all these oblique 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 Vertebrata.

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

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, which 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 vertebree 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 obliquus in-
ternus 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 internt
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 Cetacea.

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, which proceed (usually in two
layers) obliquely, from the clavicle and supraclavicle to the
fin-rays. Tne pectoral and pelvic arches themselves are im-
bedded in the lateral muscles.

In the Amphibia and all the higher Vertebrata, the muscles
of the limbs are divisible into—intrinsic, or those which 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 ventral aspect, with an anterior, or pre-axial, and a pos
terior, or post-axial, side.

THE MUSCLES OF THE LIMBS, 47

In the Vertebrata above fishes, the following muscles, which
occur in Man, are very generally represented :

Extrinsic muscles attached to the pectoral and pelvic arches,
on the dorsal aspect.—In the fore-limb, the cleidomastoideus,
from the posterolateral region of the skull to the clavicle ; the
trapezius, from the skull and spines of many of the vertebrze
to the scapula and clavicle; the rhomboidez, from the spines
of vertebrz to the vertebral edge of the scapula, beneath the
foregoing. Sometimes there is a tracheloacromialis, from the
transverse processes of the cervical vertebrze to the scapula.

On the ventral aspect, the subclavius, which 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 anguli scapulee ; 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 with the foregoing. So far, however, as the
rectt abdominis, the obliquus externus, and the fibres of the
erector spine, 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 arch,
retractors, though, owing to the relative fixity of the pelvis,
they act in protracting, or flexing, the caudal region.

The psoas minor, 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 homolegue in the fore-limb.

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

In the hind-lim», the glutceus maximus, so far as it arises
from the sacral and coccygeal vertebra, and is inserted into
the femur, repeats the relations of the latisstmus dorst. In
the absence of any thing corresponding with the sternum, or
the ribs, no exact homologue of the pectoralis major can be
said to exist, though the pectineus comes near it. The psoas

48 THE ANATOMY OF VERTEBRATED ANIMALS.

major, passing from posterior dorsal or lumbar vertebraa—the
pyriformis from sacral vertebraee—the femoro-coccygeus (when
it exists) from caudal vertebraa—to the femur, are all hypo-
skeletal muscles, without homologues in the anterior extremity.

All the other muscles of the limbs are intrinsic, taking
their origins from the pectoral or peivic arches, or from some
of the more proximal segments of the Jimb-skeleton, and hav-
ing their insertion in the more distal segments. They are
thus arranged in Man and the higher Mammalia:

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-axtal side of the spine
of the scapula; the infra-spinatus, 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 humerus.

In the hind-limb, the tensor vagine 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 gluteus maximus, which,
at first sight, would seem to be the homologue of that muscle.

The zliaeus, proceeding from the inner surface of the crest
of the ilium to the smaller trochanter, answers to the supra-
spinatus ; the gluteus medius and minimus, which arise from
the outer surface of the ilium, to the 7fra-spinatus and teres,

In the fore-limb, a muscle, the subscapularis, 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 aspect in the fore-limb, the coracobrachialis
passes from the coracoid to the humerus. In tlre 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 pectineus, and the great ab-
ductors of the femur; with the obturator externus, from the
outer side of the ischiopubic fontanelle, or obturator membrane.
The gemelli and tne quadratus femoris take their origin from
the ischium.

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

THE MUSCLES OF THE LIMBS. 49

the hind-limb. On the other hand, a muscle, the obturator
internus, 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 coracobrachialis, which arises from the inner surface
of the coracoid in many Sauropsida.

Muscles of the Antebrachium and Crus.— On the dorsal
aspect of the fore-limb, as of the hind-lmb, certain muscles
wrise 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 ; in the
hind-limb, the quadriceps extensor.

There is this difference between these two homologous
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 swpinator
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 guadriceps, 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 supinator 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 sz-
pinator longus. Corresponding with the brachialis anticus
is the short head of the biceps femoris, arising from the femur,
and inserted into the post-axial bone of the leg, the fibula.
The long head of the biceps femoris, 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

4

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 popliteus,
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 MMarsupialia and Leptilia,
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-

letely 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 digit of the manus, or little finger, im Man and the higher
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 minimi digiti. Thirdly, entering the same
expansion is one tendon of the extensor communis digitorum.

On the ventral aspect there are: first, attached to the base
of the metacarpal, the tendon of a distinct muscle, the jlexor
carpi ulnaris ; secondly, arising from the sides and ventral face
of the metacarpal, and inserted into either side of the base of
the proximal phalanx, two muscles, the interossei ; thirdly,
inserted into the sides of the middle phalanx by two slips, a
tendon of the flewor perforatus ; and fourthly, passing be-
tween these two slips, and inserted into the base of the distal
phalanx, a tendon of the jlexor 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. Jor the ten-
dons of the eatensor communis and extensor minimi dig giti are
attached to the middle and the proximal phalanges; and the
distal phalanx is specially elevated by the 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, namely:

et ie | a’,

THE MUSCLES OF THE LIMBS. 51

On the dorsal aspect: first, the peroncus tertius 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 digitorum longus.

Fie. 17.—Part of the middle digit of the manus of an Orang with the flexors and extensors
of the phalanges: mep., metacarpal bone; Ph. 1, Ph. 2, Ph. 3, the three phalanges;
xt. 1, the deep long extensor tendon from the eatensor indicis; Heat. 2, the supertfi-
cial long extensor tendon from the extensor communis ; TI. e., the interosseous short ex-
tensor; J.7:, the interosseous short flexor; F’. pns., the deep long flexor (perforans) ; &.
pis., the superiicial long flexor (perforatus).

On the ventral aspect: first, the peroncus brevis, attached
to the base of the metatarsal; secondly, two interossez ;
thirdly, a perforated flexor; and fourthly, a perforating flexor,
like those of the manus. The divisions of the ¢énterosse?,
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 interosse?, arising within the
manus or pes, and inserted into opposite sides of the proximal
phalanx; and an opponens, a muscle attached to the ventral
face of the carpus or the tarsus, and inserted into the post-
axial edge of the shaft of the metacarpal or metatarsal.

Finally, a @mbricalis 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 often regarded as muscles special to man,
such as the extensor proprius indicis and extensor minimé
digiti, 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 digits
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
interossez) 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-linb. Nevertheless, several of the muscles correspond
very closely. Thus, on the dorsal aspect, the extensor ossis
metacarpt pollicis 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 metacarpt
pollicis ; 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 the 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 radialis lon-
gus to the base of the second metacarpal; the extensor carpr
radialis brevis to the base of the third metacarpal; the exten-
sor communis digitorum to the four ulnar digits; the exten-
sor minimi digiti to the fifth digit; the extensor carpi ul

* T have seen an opponens in the hailux cf an Orang.

THE MUSCLES OF THE LIMBS. 53

naris to the base of the fifth metacarpal. In the hind-limb,
there 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
peroncus tertius,* passing from the dorsal face of the fibula
to the fifth metatarsal, is the only representative of the exten-
sor carpi ulnaris,

On the ventral aspect of the human fore-limb, two deep
flexors arise from the radius, ulna, and interosseous membrane,
and run parallel with one another, though disconnected, to
the digits. These are, on the pre-axial side—the flexor polli-
cis longus, to the distal phalanx of the pollex; and the flexor
digitorum perforans, to the distal phalanges of the other
digits.

“In the hind-limb, two homologous muscles, the flexor hal-
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 the flexor carpi radialis to the base
of the second metacarpal; the palmaris longus to the fascia
of the palm; the flexor perforatus digitorum to the middle
phalanges of the four ulnar digits; the flexor carpi ulnaris 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 plantaris ; 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 palmaris 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 achillis, and divides into slips, whick
become the perforated tendons of more or fewer of the digits.

* This muscle, which lies altogether on the dorsal face of the hind-limb,
and which J have seen only in Man, should not be confounded, as it often is,
with one or more muscles, the peronwé 8tii, 4ti, et 5t¢ digiti, which are very
often developed in other Mammalia, but arise on the ventral face of the fibula,
and send their tendons below the external malleolus to the extensor sheaths
of the fiftd:, urth and even third digits,

54 THE ANATOMY OF VERTEBRATED ANIMALS.

The flexor carpi radialis 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 may be closely connected with the tendons of the
plantaris. The peroncus brevis represents the flexor carpé
ulnaris by its insertion, but it arises no higher than the fibula,
and has no sesamoid.

Two most important muscles yet 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 gastrocnemius),
and two from the tibia and fibula (called soleus). The other
muscle is the peroncus longus, 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 soleus may pos-
sibly represent the crural part of the perforated flexor, since,
in many of the Vertebrata, 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 transversalis
pedis, 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 Zorpedo (among the Elasmobranchii), Gymnotus, Ma-
lapterurus, 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 always composed of
nearly parallel lamella of connective tissue, enclosing small
chambers, in which lie what are termed the electrical plates.
These 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 lamella are disposed parallel to the

THE ELECTRICAL ORGANS. 55

upper and under surfaces of the body; posterior in Gymno-
tws, and anterior in Malapterurus, the lamellz 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.

Fig. 18.—The Torpedo, with its electrical apparatus displayed.—d, branchia; ¢, brain; 6
electric organ; g, cranium; me, spinal cord; », nerves to the pectoral fins; nl, nerv
laterales ; np, branches of the pneumogastric nerves going to the electric organ; 0,

eye.

In 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 Malapte-
rurus, 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 Nervous System: the Encephalon.—In all verte-
brated animals except Amphioxus, the brain exhibits that
separation into a fore-brain, mid-brain, and hind-brain, which

56 THE ANATOMY OF VERTEBRATED ANIMALS.

results from its embryonic division, by two constrictions, into
the three thin-walled vesicles—the anterior, middle, and poss
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
thickening of their sides and floors. The cavity of the ante-
rior vesicle is, in the adult human brain, represented by the
so-called third ventricle ; that of the middle vesicle, bv the
iter a tertio ad quartum ventriculum ; 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.

ya &
bY,

4 _o7,

a OS
vy)
A
A i
4
Fx. a
YY
4)
CO)

Yih WY
Y
3 Y}
I. Pn-G Z

YY ~<-----

LE.

LAY

fia. 19.—Diagrammatic horizontal section of a Vertebrate brain. The following letters
serve for both this figure and Fig. 20: Jb, Mid-brain. What lies in front of this is the
fore-brain, and what lies behind, the hind-brain. JZ. #%.,the lamina terminalis; O77, the
olfactory lobes; ZZmp, the hemispheres; 7%. #, the thalamencephalon; Pn, the pineal
gland; Py, the pituitary body; Jf, the foramen of Munro; CS, the corpus striatum ;
Th, the optic thalamus; CQ, the corpora quadrigemina; CC, the crura cerebri; Cb, the
cerebellum; PV, the pons varolii; 170, the medulla oblongata; J, olfactorii; ZZ, optici;
ITT, point of exit from the brain of the motores oculorum; JV, of the pathetici; VJ, of
the abducentes; V-XVJZ, origins of the other cerebral nerves. 1, olfactory ventricle ;
2, lateral ventricle; 3, third ventricle; 4, fourth ventricle; +, ter a tertio ad quartum
nentiiculum.

THE ENCEPHALON. 57

The posterior part of the roof is not converted into nervous
matter, but remains thin and attenuated; the ependyma, or
lining of the cerebral cavity, and the arachnoid, or serous
membrane which 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 pons
varolit, 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
myelencephaton) behind, and the cerebellum with the pons
varolii (which together constitute the metencephalon) in
front. :
The floor of the middle cerebral vesicle thickens and
becomes converted into two great bundles of longitudinal
fibres, the crura cerebri, Its roof, Givided into two, or four,
convexities by a single longitudinal, or a crucial, depression,
is converted into the “optic lobes,” corpora bigemina or
gquadrigemina. 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 ¢ter a

tiq. 20.—A longitudinal and vertical section of a Vertebrate brain-—The letters as before
The lamina terminaiis is represented by the strong black line between #2 and 3.

tertio ad quartum ventriculum), are the components of the
mid-brain or mesencephalon.
The anterior cerebral vesicle undergoes much greater

58 THE ANATJMY OF VERTEBRATED ANIMALS.

changes than 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 lobe (or rhinencephalon). By
the development of these processes the anterior vesicle

ecomes 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 infundibulum, the blind end of which is
connected with the pituitary body, or hypophysis cerebri. Tts
sides thicken greatly, acquire a ganglionic structure, and
become the optic thalami. 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 optic thalamus. The line of demar-
cation between the two corresponds with the lower lip (tenia
semicircularis) of the aperture of communication (called the
foramen of Munro) between the third ventricle and the
cavity of the cerebral hemisphere, which is now termed the
lateral ventricle. Inthe 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 THE BRAIN, 59

teriorly, these longitudinal fibres are continued backward and
downward along the inner wall of the cerebral hemisphere,
following the junction 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
hippocampus 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 forntx. Behind this union the bands
receive the name of the posterior pillars of the fornix.

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

In the Mammalia, a structure, which is absent in other
Vertebrata, makes its appearance ; and, in the higher members
of that class, this corpus callosum is the greatest and most im-
portant mass of commissural fibres. IJ¢ 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 lucidum, with
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 Mammalia, they extend forward
over the olfactory lobes, and backward over the optic lobes
an1 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 carpus striatum, and it becomes distinguished into regions,
or lobes, which are not separated by any very sharp lines of
demarcation. These regions are named the frontal, parietal,

60 THE ANATOMY OF 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 ventricles are prolonged
into the frontal, occipital, and temporal lobes, and acquire
what are termed their anterior, posterior, and descending
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 (B), and tem-
poral ((’), 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 gyrus in the
higher Mammalia, 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-
bellum when the brain is viewed from above. What in the
Rabbit 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 angular, gyrus. ‘Two other sets
of gyri, more or less parallel with this, are visible upon the
outer surface of the hemispkere; and at the entrance of the

THE MODIFICATION OF THE BRAIN. 61

Ta, 21.—Lateral views of the brains of a Rabbit, a Pig, and a Chimpanzee, drawn of nearly»

the same absolutesize. The Rabbit's brain is at the top; the Pig’s, in the middle, the
Chimpanzee’s, lowest.— OJ, the olfactory lobe; A., the frontal lobe; B., the occipital
lobe; @., the temporal lobe; Sy., the Sylvian fissure; Jn., the insula; S.Or., supra-
orbital; S.F., IfF., I.F., superior, middle, and inferior frontal gyri; A.P., antero-pari-
etal; P.P., postero-parietal gyri; #, sulcus of Rolando; P.//, postero-parietal lobule ;
O.Pf., external perpendicular or occipito-temporal sulcus; An, angular gyrus; 2, 3, 4,
annectent gyri; A.7., “.7., P.T., the three temporal, and S.0e., M.Oc., I.Oc., the three

occipital gyri.

62 THE ANATOMY OF VERTEBRATED ANIMALS.

Sylvian fissure, at Jn, there is an elevation which answers to
the tnsula, 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 (substantee perforativ) are completely
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 Mammalia. The
fissure of Rolando (#2) divides the antero-parietal gyrus (A. P)
from the postero-parietal (P,P). These two gyri, with the
postero-parietal lobule (P./.), and part of the angular gyrus
(An), constitute the Parietal lobe. The frontal lobe, which
lies anterior to this, the occipital lobe, which lies behind it,
and the temporal lobe, which lies below it, each present three
tiers of gyri, which, in the case of the frontal and occipital
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
(S. Or.), presents many small sulci and gyri.

_ On the inner face of the cerebral hemisphere (Fig. 22) the
oly sulcus presented by the Rabbit’s brain is that deep and
broad depression (/Z) 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 (#) is much narrower and less conspicuous; and a
marginal (M) and a calossal (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 (Lp). The calcarine suicus (Ca)
causes a projection into the floor of the posterior cornu,
which is the hippocampus minor ; while the collateral sulcus
(Coll) gives rise to the eminence of that name in both the
posterior and descer.ding cornua. The hippocampal sulcus
(ZZ) is relatively insignificant, and the lower edge of the tem-
poral lobe is formed by the posterior temporal gyrus.

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

THE MODIFICATION OF THE BRAIN. 63

wa

€13. 22.—Inner views of the cerebral hemispheres of the Rabbit, Pig, and Chimpanzes,
drawn as before, and placed in the same order. O2J., olfactory lobe; C.c., corpus callo-
sum; A.c., anterior commissure; H., hippocampal sulcus; Un., uncinate; J/., mar-
ginal; (., callosal gyri; Z.p., internal perpenuicular; Ca., calcarine; Coll., collateral
sulci; 2’, fornix.

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

64 THE ANATOMY OF VERTEBRATED ANIMALS.

larger, more horizontal, and possesses more of a rostrum in
the Chimpanzee, it is still larger, somewhat deflexed, 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 mammillare, 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
jlocculi, 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 arez, the so-called corpora trapezoidea.

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 Chim-
panzee, the relatively still smaller cerebellum is completely
covered; the vermis is very 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
differs far less from that of the Chimpanzee than that of the
latter does from the Pig’s brain.

The Myelon.—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, which 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-
vous 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 i» an an-
terior (or ventral) and a posterior (or dorsal) horn. Nerve-

|
f

THE MYELON. 65

FIG 23.—A diagrammatic view of the Chief Trunks of the Cerebro-spinal and Sympathetie

Nervous Systems of Rana esculenta seen from below (twice the size of nature).—I. The
olfactory nerves. N. The olfactory sac. II. The optic nerve. O. The eye. ZL. op.
The optic lobes. Za. Optic tracts passing from the optic lobes to the chiasma, behind
which lies the pituitary body. Ill. Oculomotorius. IV. Patheticus. V-. The tri-
geminal, with which the adducens (VI.), facialis (VII.), and the upper end of the sym-
pathetic (VS.), are closely connected. Branches of this nervous plexus are V.a, the
nasal and ophthalmic branches of the fifth and the abducens. V, 6, c, d, the palatine,
maxillary, and mandibular branches of the fifth. V, e, the tympanic branch into whick
the proper facial nerve (VII.) enters, and, with a branch of the vagus, forms the so-
called facial nerve of the Frog, #. VIII. The auditory nerve. X., with its branches
X1, X2, X3, X4, represents the glossopharyngeal and the vagus. The medulla ob
longata (Myelencephalon) ends, and the medulla spinalis (J/ye/on) begins, about the
region marked by the letter J/, J£1-10, the spinal nerves. V2, the brachial nerves,
M 7, 8, 9, the ischiatic plexus, from which proceed the crural (N. ¢.) and ischiatic (N. 7.)
nerves. S. The trunk of the sympathetic.. S.M. The communicating branches with
the spinal ganglia. S 1-10. The sympathetie ganglia.

65 THE ANATOMY 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
vertebre through, or between, which they pass out (Fig. 23).
Each nerve has two roots, one from the dorsal, and one from
the ventral, region of its half of the cord. The former roct
has a ganglionic enlargement, and only contains sensory
fibres; the 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 own 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” (olfactoriz) 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” (optici) are the second pair of cere-
bral nerves. In the Lampreys and Hags (Marsipobranchii)
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 (TZé/eostei), or are fused together into a chiasma
‘Ganoidei, Elasmobranchii, and all the higher Vertebrata).
In the higher Vertebrata, again, the fibres of the optic nerve
become connected chiefly with the mesencephalon.

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

The third (motores oculorum) and fourth (pathetic?) pairs
of nerves are distributed to the muscles of the eye; the third
to the majority of these muscles, the fourth to the superior

* Amphioxus appears to be an exception to this, as to most other, rules of
Vertebrate anatomy.

THE CEREBRAL NERVES. 67

oblique muscles. The third pair of nerves 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 Valve 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
Jith 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 orbito-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 has
two very distinct roots, a dorsal sensory, provided 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 (e7Jiary) ; the superior maxillary
another (sphenopalatine or Meckelian), 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 supplies the external straight muscles of
the eye; with the muscles of the nictitating membrane, and
the retructor bulbi, or musculus choanoides, when such mus-
cles exist.

The seventh pair ( faciales) supplies the superficial facial

68 THE ANATOMY OF VERTEBRATED 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 Myxinoid fishes
there are no motor nerves of the eyeball; but, in the Lamprey,
the rectus externus and inferior, and the obliquus 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 obliquus 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, Hlasmobranchii, 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 Amphibia, 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, a palatine, 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 Meckelian, 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 with
the inferior maxillary division of the fifth nerve.

The eighth pair (auditoriz) is formed by, the nerves of the
organ of hearing.

The ninth pair (glossopharynge’) is especially distributed to
the pharyngeal and lingual regions of the alimentary canal,
and, primarily, supplies the boundaries of the second visceral
cleft.

The tenth pair ( pneumogastrici or vagi) consists of very

*T am greatly 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, which 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 Lchthyopsida they give
off, in addition, long /atera/ nerves to the integuments of the
sides of the body. In the higher Vertebrata, 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 (accessorit) 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 vertebree, and are inserted into the pec-
toral arch. 2

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

The twelfth and last pair (hypoglosst) are the motor nerves
of the tongue, and of some retractor muscles of the hyoidean
apparatus,

In the Ichihyopsida the first cervical nerve supplies the
distributional area of the hypoglossal; but in all the abran-
chiate Vertebrata 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 Vertebrata, 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
cranium 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 alisphe
noid, |

70 THE ANATOMY OF VERTEBRATED ANIMALS.

e. 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 prodtic.

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, 0, c, d, when surrounded by bone, and
well defined, are called respectively : a, the olfactory foramen ;
6, the optic foramen ; c, the foramen ovale ; d, the foramen
lacerum posterius. '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
change.

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 seventh
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 enclosing the first visceral cleft. In like man-
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
third and fourth arches and to the third cleft; and, in bran-
chiate Vertebrata, the other anterior branches of the pneumo-
gastric are similarly distributed to the successive branchial
arches, the two divisions of each branch enclosing a branchiai
cleft.

The second and the third divisions of the trigeminal 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-palatine
process, and the outer side of the trabecula eranii—the orbite
nasal fissure representing the cleft between the two.

Considerations of this kind suggest that the trabeculz and
the maxillo-palatine processes may represent pre-oral visceral
arches, which are bent forward; and, in the case of the fra-
becul, coalesce with one another. Such an hypothesis would
enable us to understand the signification of the naso-palatine

THE SYMPATHETIC NERVES. +B hae

canal of the Myxinoid fishes, which would be simply the in-
terspace, or passage, between the trabeculae (which must have
originally existed if ever they were distinct visceral arches)
not yet filled up; and the anomalous process of the roof of the
‘ oral cavity, which extends toward the pituitary body in the!
embryos of the Vertebrata 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 hyoidean, 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
rae 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 Vertebrata except Aimphioxus and
the Marsipobranchii. 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 sympathetic 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 Marsipobranchii, the place of the sympathetic ap-
pears to be taken, to a great extent, by the pneumogastric;

72 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’
already 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 Apparatus acquires no higher complication
than this, being either a single sac (Amphioxus (?) 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 Mammalia, are
sometimes closed by the mucous membranes of the nasal and
oral cavities, and sometimes not. In the latter case they are
the canals of Stenson, 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. They are called,
after their discoverer, the “ organs of Jacobson.”

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 cavity 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 7v/s. The integument around the cor

THE EYE. 73

nea, growing out into a fold above and below, results in the
formation of the eyelids, and the segregation of the integu-
ment which they enclose, as the soft and vascular conjunctiva,
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
membrane, moved by a proper muscle or muscles. Special
zlands —the lachrymal externally, and the Hurderian 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 eye has a totally distinct ori-
gin, Very early, that part of the anterior cerebral vesicle
_ which eventua.ly 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,
surrounding itself with a strong 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 Vertebrata 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 Myzxine, 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 Myzxine, this rudimentary eye
is hidden by muscles and integument. It appears doubtful

+

74 THE ANATOMY OF .VERTEBRATED 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 (Amblyopsis) and the
Mole, they have no functional importance. In the Jchthy-
opsida and Sauropsida, but not in Mammalia, the sclerotic
is often partially ossified, the cssification 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 rect?. The other two are connected with
the upper and the lower margins of the orbit respectively, and
pass thence to the outer side of the bulb. These are the szpe-
rior and the inferior obliquz. In many Reptiles and Mam-
mals a continuous funnel-shaped sheet of muscle, the muscu-
lus choanoides, lies within the four rect/, and is attached to
the circumference of the posterior moiety of the ball ofthe eye.
It would appear, from the distribution of the nerves, which
has already been described, that the musculus choanoides,
the external rectus, and the nictitating muscle, constitute
a group of eye-muscles morphologically distinct from the other
three recti, the obliqui, and the levator palpebre superioris,
In many Reptiles, and in the higher Vertebrata, the eyelids
are closed by circular muscular fibres, constituting an orbicu-
laris palpebrarum, and are separated by straight fibres pro-
ceeding from the back of the orbit, usually to the upper eye-
lid only, as the levator palpebre superioris ; but sometimes to
both lids, when the lower muscle is a depr essor palpebree infe-
rioris,

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

In Lacertilia, Crocodilia, 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,
und usually becomes connected with the capsule of the lens,
This is the pecten, or marsupium.

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

THE EAR. 15

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 semicircular canals—the anterior
and posterior vertical, and the external or horizontal canals
of the membranous labyrinth. ‘The body of the sac remains,
tor the most part, as the vestibule ; but a cecal process, which
eventually becomes shut off from the vestibule, is given off
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, Amphioxus, no ear has yet
been discovered. The Hag (Myzine) 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 labyrinth, externally, and present no merely
membranous gaps, or fenestra, toward the first visceral cleft,
or the space which represents if.

But in higher Vertebrata (Amphibia, Sauropsida, Mam-
malia), 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 areze, which consequently appear like windows with
membranous panes, and are termed the fenestra ovalis and the
Senestra rotunda.

The fenestra ovalis is situated in that part of the periotic
mass which bounds the chamber containing the membranous
vestibule externally ; and it isalways 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 ovalis is situated in the line of junction of these two
bones. The fenestra rotunda, on the other hand, is below
the fenestra ovalis, and lies altogether in the opisthotic. It
forms part of the outer wall of the cavity in which the mem-
branous cochlea is lodged.

In the Sauropsida and Mammalia, this membranous coch-
lea, become flattened and bandlike, and its communication
with the vestibule obliterated, is lodged in a conical cavity, in
such a manner as to divide that cavity into two. portions,
calied scale, which only communicate at their apices. The
base of the one scala, called scala vestibuli, opens into the

76 THE ANATOMY OF VERTEBRATED ANIMALS.

cavity which contains the membranous vestibule: that of the
other, scala tympant, abuts against, and is as it were stopped
by, the membrane of the fenestra rotunda. The cavity of the
membranous cochlea stretched between, and helping to divide,
these two scale, 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 Mammaiia, it becomes coiled in a flat or conical
spiral of one and a half (Cetacea, Hrinaceus) to five (Celo-
genys Paca) 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 scale
vestibuli 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 difference 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 of Vertebrata 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 membrana 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 Hustachian 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 fenestre ; 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 the fenestra ovalis become mechanically
connected. In all these animals the mandible is connected
with the skull by the intermediation of an os guadratum.

But, in the Mammatia, the mandible is articulated directly
with the squamosal, and the guzdratum is converted into one

THE EAR. "4
of the so-called ossicula auditds, and named the malleus. The
malleus becomes attached to the membrana tympani, by a
special process ; while its other extremity, which was continu-
ous with Meckel’s cartilage in the embryo, is converted into
the processus gracilis, or Holianus, 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 quadratum. Thus the stapes
stands out at right angles to the hyoid cornu, and the latter
becomes divisibie into a supra-stapedial part, and a part which
lies below the stapes, and answers to the styloid process, or
stylohyal, of the Mammalia. The supra-stapedial part is rep-
resented by cartilage, or ligament, in other Sauropsida, but
seems not to ossify. In the Mammalia (B, Fig. 24), the su-
pra-stapedial part ossifies, becomes the incus, and its proximal
end is usually articulated by a synovial joint with the madleus
(= quadratum). A distinct ossification, the os orbiculare,
usually arises at that part of the hyoidean cartilage in which
the stapes and the incus unite. That part of the hyoidean
cartilage which is converted into the styloid process is gen-
erally connected with the orbiculare by muscular tibres, which
constitute the stapedius muscle. On the other hand, the pos

Pe.
Msn.

Fic. 24.—Diagram of the skeleton of the first and second visceral arches in a Lizard (A),
Mammal (B), and an Osseous Fish (C).

The skeleton of the first visceral arch is shaded, that of the second is left nearly unshaded.
J. First visceral arch. Mck. Meckel’s cartilage. Art. Articulare. Qu. Quadratum.
Mpt. Metapterygoid; If. Malleus; p.g., Processus gracilis. JJ. Second viscerel arch.
Hy. Wyoidean cornu. Sé¢. H. Stylohyal. S. Stapedius. Stp. Stapes. S&. Stp. Supra-
stapedial. 4M. Hyomandibular. The arrow indicates the first visceral cleft. Pe. The
periotic capsule. Lig. The pterygoid.

terior, or short process of the incus, is connected by hgament
with that part of the periotic mass into which the styloid pro-

78 THE ANATOMY OF VERTEBRATED ANIMALS.

cess is directly continued, and it is hard to say whether the
styloid part of the hyoid is continued into the incus by these
ligaments or by the stapedius. But, however this may be, the
malleus 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 Chimera, Dipnoi, and
many Amphibia, into a single cartilaginous plate.

In the Mammalia, and to some extent in Aves, osseous
matter is deposited in the fibrous tissue which surrounds the
sides and base of the tympanic membrane, and gives rise to a
special tympanic 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 that’lining the fauces. When the sense is well de-
veloped, the mucous membrane is raised into numerous papillz
of various forms, and is well supplied with filaments from the
glossopharyngeal nerve.

The sense of Zouch is diffused over the integument 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 Vertebrata, the
nervous papille, containing “ tactile corpuscles,” and the long
facial hairs, the papillze of which are well supplied with nerves,
termed vibrisse, 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. ,The walls of the sacs, or canals,
are abundantly supplied with nerves, and the terminations of
the latter enter rounded papilla, which project into the gelati-
nous contents, These sensory organs are known as the “ or.

THE LIVER AND THE TEETH. ng
gans of the lateral line,” or “mucous canals ;” and they
were formerly supposed to be the secretory glands of the
slimy matter which coats the bodies of fishes, and which is
really modified epidermis.

The Alimentary Cana!.—This part of vertebrate organi-
zation always exhibits a differentiation into mouth, pharynx,
cesophagus, 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 ce@ca@ are
frequently developed trom the former.

The stomach and intestine are invested by a peritoneal
membrane, and connected, by mesogastric and mesenteric 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
Amphioxus, Myxine, and the Leptocephalidce) developed in
close proximity to the stomach. A pancreatic gland very
generally pours its secretion into the anterior end of the intes-
tine. Salivary glands very commonly open into the mouth;
and, in the higher Vertebrata, anal glands are not unusually

eveloped 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 always
ultimately resolvable into czecal 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 Vertebrata 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. -Amphioxus stands
alone among vertebrated animals, in having a cxcal diverticu-
lum of the intestine for a liver.

The Teeth.—Teeth, in Mollusca and Annulosa, are always

80 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 bétween 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 “baleen” 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 by
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 papilla of the mucous mem-
brane, which may be exposed, but are more usually sunk in a
fold or pit, the roof of which 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 milk dentition, and a second, or permanent dentition.
The deciduous dentition, when most completely developed, con-
sists of incisor, canine, and molar teeth. ‘The incisors are
distinguished from the rest by the lodgment of the upper set
in the premaxillz, 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 formula is a convenient combination
of letters and figures for making the number and disposition
of the teeth obvious. Thus, let di, dc, 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 cach side of each jaw, we shall have the dental

DENTAL FORMULE. 81

furmula of a given animal. The dental formula of a child
D) ns

over two years of age is thus—di. - de. a

which means that the child shouid have two incisors, one

canine, and two molars on each side of each jaw.

The neck of the sac of each deciduous tooth gives of a
diverticulum, in which 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 d, are used for the
permanent incisors and canines;- but the permanent teeth,
which replace the deciduous molars, are called premolars,
and have the symbol ym. 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 symbol m. Thus the
formula of the permanent dentition in Man is written:
a Bee ae pin ee m geo there being two incisors
ett 22 38 :
one canine, two premolars, and three molars on each side
above and below. It is a rule of very general application
among the Mammalia, 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 wear 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 follows 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 vertebrae into the cesophagus,
And, in the highest. Vertebrata, teeth are confined to the pre-
maxilla, maxille, and mandible.

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

B2 THE ANATOMY OF VERTEBRATED ANIMALS.
passes into a cardiac aortic trunk, while the posterior end is
continuous with the great veins which bring back blood from
the umbilical vesicle—the omphalomeseraic 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 its
fellow, to the hinder part of the body, as a primitive subverte-
bral aorta. The two primitive aorte very soon coalesce
throughout the greater part of their length into one trunk,
the definitive 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-
brata, and more in the lower, are successively developed,
behind the first, in the other visceral arches, and further con-
nect the cardiac and subvertebral aorteze.

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,
(Hie 25, A, B,C, D, E.)

in the higher AmpAzbia, which, though branchiate in the
young state, become entirely air-breathers in the adult con-
dition, such as the Batrachia (Fig. 25, F) and Cecilia, 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 Batrachia,
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 ZLacer-
tilia ; or to one pair, as in other Septilia ; or to a single
arch, as in Aves and Mammalia. The aortic arches thus
retained are, in the Lizards in question, the third and the
fourth pairs in 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 give 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 subvertebral 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.

7 Mn. Hy. Bri Br? Br Pea Se ap Br: ° Br?

| OOOCORCAm

TS Ve OV VAC Vi We Pe

AD.

E.

Phewe Mea aw

Fic, 25.—A diagram intended to show the manner in which the aortic arches become modi-
fied in the series of the Vertebrata.

A. A hypothetically perfect series of aortic arches, corresponding with the nine postoral yis-
ceral arches, of which evidence is to be found in some Sharks and Mar sipobranchit.
AC. Cardiac aorta; AD. Dorsal or subvertebral aorta. 1-1x the aortic arches corre-
sponding with J/m., the mandibular; Hy., the hyoidean, and &r.'—#r.7, the seven
branchial visceral arches. 1, 0, I, Iv, V, VI, Vil, the seven branchial clefts. Te tirst

84 THE ANATOMY OF VERTEBRATED ANIMALS.

wisceral 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 Heptanchus, which has seven
branchial clefts. Sp. The remains of the first visceral cleft as the spiracle. Branchix
are developed on all the arches.

C. Lepidosiren.—The first arch has disappeared as such, and the first visceral cleft is ob-
literated. Internal branchize are developed in connection with the second, fifth, sixth,
and seventh aortic arches; external branchiz in connection with the fourth, fifth, and
sixth. A.—The pulmonary artery. The posterior two visceral clefts are obliterated.

D. A Teleostean Fish.—The first aortic arch and first visceral cleft are obliterated as before.
The second aortic arch bears the pseudo-branchia (Ps.£.), whence issues the ophthalmic
artery, to terminate in the choroid gland (C/.). ‘The next four arches bear gills. The
seventh and eighth arches haye been observed in the embryo, but not the ninth, and
the included clefts are absent in the adult,

E. The Axolotl (Sivedon), a perennibranchiate amphibian. The third, fourth, fifth, and
sixth aortic arches, and the anterior four branchial clefts, persist. The first visceral
cleft is obliterated.

F The Frog.—The three anterior aortic arches are obliterated 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 obliterated in the adult.

The embryonic aorta gives off omphalomeseraic branches
(Fig. 26, 0) to the umbilical vesicle ; and ends, at first, in the
hypogastric arteries (which are distributed to the allantois in
the abranchiate Vertebrata), and a median caudal continuation.
The blood from the umbilical vesicle is brought back, as before
mentioned, by the omphalomeseraic veins (Fig. 26, 0’), which
unite in a dilatation close to the head; the dilatation (sinus
venosus) receives, on each side, a short transverse venous
trunk, the ductus Cuviert (Fig. 26, DC), which 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 wmbilical
vein, or veins (Fig. 26, «), 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 vena 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, which is not only the
vein of the umbilical sac but also that of the intestine, and
converts it into a meshwork of canals, which communicate, on
one side, with the cardiac part of the vein, and, on the other
side, with its intestinal part. The latter is thus converted into
the vena porte (Fig. 26, vp), distributing the blood of the
stomach and intestines to the liver; while the former becomes

THE DEVELOPMENT OF THE VASCULAR SYSTEM. 85

the hepatic vein (vh), 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, Dv).

Fro. 26.—Diagram of the arrangement of the principal vessels in a human feetus.—/7, the
heart; ZA, the aortic trunk or cardiac aorta; c, the common carotid; ¢’, the external
carotid; c/’, the internal carotid; s, subclavian; v, vertebral artery; 1, 2, 3, 4, 5, ths
aortic arches—the persistent left aortic arch is hidden. A’, subvertebral aorta; 0, om-
phalomeseraic artery, going to the umbilical vesicle v, with its vitelline duct dv; 0, om-
phalomeseraic vein ; wp, the vena porte; Z, the liver; ww, the hypogastric or umbilical
arteries, with their placental ramifications, w/’ w/’; w/, the umbilical vein; Do, the ductus
venosus; wh, the hepatic vein; cv, the vena cava inferior; vil, the iliac veins; a2, a vena
azygos; vc’, a vena cardinalis posterior; DC, a ductus Cuvieri; 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 porte. 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.

86 THE ANATOMY OF VERTEBRATED ANIMALS.

Of the three veins which 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 sw-
perior cave. Or, as very often happens in the higher Verte-
brata, the left ductus Cuvieri becomes more or less obliterated ;
the veins which properly open into it acquiring a connection
with the right ductus, which then remains as the sole superior
eava. ‘The posterior cardinal veins give off anastomosing
branches, which are converted into the venw azygos ; the an-
terior cardinal veins become metamorphosed into the external
jugular veins and vence innominate.

In Fishes, the sinus venosus and the cardinal veins persist
throughout life; but the anterior cardinal veins, which bring
back the blood from the head and from the anterior extremi-
ties, are called venw jugulares.

The caudal veins are either directly continued into the
cardinal veins, as in Marsipobranchii and Hlasmobranchii, or
branch out into the kidneys, as in many Zéleoste?. 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 Amphioxus and Myxine
the vein is rhythmically contractile, and forms a portal heart.

In most Amphibia and Reptilia 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 VEnce Cave.

The vena 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 by 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 porte in the substance of the kidneys. This
renal portal system is less developed in Feptilia than in Am-
phibia. 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 the abdominal cavity, either as
two trunks, or united into one. These vene abdominales an-
teriores are eventually distributed to the liver, along with the
branches of the proper venc porte.

In Birds, the sinus venosus is not distinct from the right
auricle, and there are two anterior venw cave. 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 two 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 cave are frequently reduced to
one, the right. The vena 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 composed
exclusively of radicles proceeding from the chylopoietic
viscera.

Many of the veins of Amphioxus, the portal vein of Myz-
ine, dilatations of the caudal vein in the Hel, the venze cave
and the iliac and axillary veins of many Amphibia, 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 Vertebrata 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
mirabilia.

Modifications of the Heart.—Great changes go on in the
structure of the heart, pari passu with the modifications of the

88 THE ANATOMY OF VERTEBRATED 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 two, so that a right auricle and
right ventricle become separated from a left auricle and left
ventricle. A similar longitudinal division is effected 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 the circulation is determined.
The septum between the auricles remains incomplete for a
much longer period than that between the ventricles—and
the aperture by which the auricles communicate is called the
foramen ovale.

In the adult state of Aves and Mammalia, 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 Crocodilia, 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 Leptilia,
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 Chelonia), and the blood of the
left auricle tows 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 cavum pulmonale); the ostium of the pulmonary artery
being farthest from, and that of the right aortic arch nearest
to, the cavum arteriosum.

In all Amphibia, the spongy interior of the ventricle is
andivided, and the heart is trilocular, though the auricular
zeptum is sometimes small and incomplete. In all Pisces, ex-
cept Lepidosiren, there is no auricular septum. In Amphé-

THE MODIFICATIONS OF THE HEART. 89

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

In the Ganoide?, the Hlasmobranchit, and the Amphibia,
the walls of the enlarged commencement of the cardiac aorta,
called the bulbus aortw, contain striped muscular fibre, and
are rhythmically contractile.

The Ganoidet and Llasmobranchit 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 Vertebrata 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 which, 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
laryngeal, which 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 inte
the thorax.

The Blood- Corpuscles.—Corpuscles are contained in the
blood of all Vertebrata. In Amphioxus they are all of one
kind, colorless and nucleated. The genus Leptocephalus,
among the 7Zeéleostez, is said to possess the same peculiarity ;

BO THE ANATOMY OF VERTEBRATED ANIMALS.

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

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

In Mammalia, 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 Mammalia are spheroidal, and
exhibit amzeboid movements; the red corpuscles are flattened,
usually circular, but sometimes oval ( Camelide) disks, devoid
of contractility.

The Lymphatic System.—This system of vessels consists,
chiefly, of one or two principal trunks, the thoracic duct, or
ducts, which underlie the vertebral column, and communicate,
anteriorly, with the superior vense cave, or with the veins
which open into them.

From these trunks, branches are given off, which ramify
through all parts of the body, except the bulb of the eye, the
cartilages, and the bones. In the higher Vertebrata, 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-system.

The lymphatics open into other parts of the venous sys-
tem besides the affluents of the superior cave. In Fishes
there are, usually, two caudal lymphatic sinuses which open
into the commencement of the caudal vein. In the Frog, four
such sinuses communicate with the veins, two in the coccy-
geal, 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 Lymphatic hearts. 'The posterior pair of
these hearts, or non-pulsating sinuses corresponding with
them, are met with in Aepétilia and Aves.

THE RESPIRATORY ORGANS. 91

Accumulations of indifferent tissue in the walls of some of
the lymphatic sinuses are to be met with in Fishes; but it is
only in the Crocodilia, among Reptilia, that an accumulation
of such tissue, traversed by lymphatic canals and blood-vessels,
is apparent, as a Lymphatic gland, in the mesentery. Birds
possess a few glands in the cervical region; and, in MMam-
malia, they are found, not only in the mesentery, but in many
parts of the body.

The Spleen is substantially a lymphatic gland. The Zhy-
mus—a glandular mass with an internal cavity, but devoid of
any duct—which is found inall Vertebrata except Amphiozus,
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 lower Vertebrata, but single in Mammalia.

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 well 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 Lymph 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 branchic 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 branchic 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-
chize of some fishes) even to the mandibular arch. The bran-
chize are always supplied with blood by the divisions of the
cardiac aorta; and the different trunks which carry the aérated
blood away, unite to form the subvertebral aorta, so that all
vertebrated animals with exclusively branchial respiration
have the heart filled with venous blood.

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

2 THE ANATOMY OF VERTEBRATED ANIMALS.

chi project freely from the visceral arches to which they are
attached, on the exterior of the body; and in some Amphibia,
such as the Axolotl (Stredon), they retain their form of eater-
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 Amphibia, the branchiz 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, with which 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 pharynx, cesophagus, or stomach. But
such air-sacs—even when they remain permanently connected
with the exterior by an open passage or pneumatic 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 cf
the posterior end may retain the smooth condition of the em-
bryonic lung. In Chelonia and Crocodilia, 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, which 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 Amphibia, such as Proteus, part of the 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 Chamceleonide, and the principal bronchial tubes termi-
nate in large air-sacs in Aves.

The Larynx and the Syringz.—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 cartilage 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 reéntering angle of the thyroid cartilage, and
between them lies a slit-like passage, the glottis. This is cov-
ered by a cartilage, the epiglotiis, attached to the reéntering
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 ligaments. The in-
ner surfaces of these end below in the false vocal cords, be-
tween which and the true chord vocales lie recesses of the
mucous membrane, the ventricles of the laryux.

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

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

The Mechanism of Respiration.—The mechanism by which
the aérating 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 vzall
of the Ascidians. Most Fishes breathe by taking aérated wa-
ter in at the mouth, and then shutting the oral aperture, and
forcing the water through the branchial clefts, when 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

54 THE ANATOMY OF VERTEBRATED ANIMALS.

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

In most Reptilia, and in all Aves and Mammatia, 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 feptilia, 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 lungs, into the very 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 Reptilia (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 /a-
titce, or struthious 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 Mammalia, there are two equally-important
respiratory pumps, the one sterno-costal, the other diaphrag-
matic. The diaphragm, tiough 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 Organs.—The higher Vertebrata 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 Wolfian bodies, the latter the true
Kidneys.

THE REPRODUCTIVE ORGANS. 95

The Wolffian bodies make their appearance very early, on
each side of the ventral aspect of the spinal region of the em-
bryo, 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, ana precedes
the tubuli.

The Aidneys appear behind the Wolffian bodies, and, ap-
parently, independently of them; their ducts, the wreters, 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 off from the rest by the constriction
and obliteration of the cavity of an intermediate part, and its
conversion into the urachus, that gives rise to the urinary
bladder. The ultimate secreting tubuli of both the Wolffian
body and the kidney, are alike remarkable for ending in dila-
tations which embrace convoluted capillaries—the so-called
Malpighian tufts. Neither Wolffian bodies nor kidneys have
been observed in Amphioxus. It is doubtful whether true
kidneys are developed in Jchthyopsida, 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, which place that cavity in direct communi-
cation with the exterior. In many fishes, the Ovaries become
tubular glands, provided with continuous ducts, which open
externally, above and behind the anus. But, in all other Ver-
tebrata, 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 A/tillerian ducts.

The Millerian 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 le close to the ovary, and become open and
dilated to form the so-called ostia. Beyond 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 Miillerian ducts undergo no
further modification of any great morphological importance ;
but, in the monodelphous Mammalia, 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 Miillerian ducts are primarily converted into a single
vagina with two wert opening into it; but, in most of the
Monodelphia, the two uteri also more or less completely coa-
lesce, until both Miillerian ducts are represented by a single
vagina, a single uterus, and two Fallopian tubes. ‘The didel-
phous ‘Mammalia have two vagine which may, 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 Miillerian 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 Amphiowus and in the Marsipo-
branchii, this tissue appears to pass directly into spermatozoa ;
but, in most Vertebrata, 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
body, certain of the tubuli of which become 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 seminalis is a

THE REPRODUCTIVE ORGANS. 97

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

We MM

Wwe mM a a
bj cc) i
Sj

| =)

3 a
ial cat

|

| See

q it

eee

\I] frei!

Bt |) ae

oe i pa

J iE:

A
sa

‘.
Me,

‘
*
TT NS

WA Csp

Fic. 27.—Diagram exhibiting the relations of the female (the left-hand figure, ¢) and of the
male (the right-hand figure, ¢) reproductive organs to the general plan (the middle fig-
ure) of these orgaus in the higher Vertebrata.

Cl, the cloaca; #, the rectum; Bi, the urinary bladder; U, the ureter; K, the kid-
ney; Uh, the urethra; G, the genital gland, ovary, or testis; W, the Wolffian body;
Wd, the Wolffian duct; J, the Miillerian duct; Pst, prostate gland; Cp, Cowper's
gland; Csp, the corpus spongiosum; Cc, the corpus cayernosum.

In the female, V, the vagina; Ué, uterus; Fp, the Fallopian tube; G¢, Gaertner’s
duct; P.v, the parovarium; A, the anus; Cc, C.sp, the clitoris. In the male, Csp, Ce,
the penis; U7, the uterus masculinus; Vs, vesicula seminalis; Vd, 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-
fian 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 Téleoste?. In all other Vertebrata
there is either a cloaca, or common chamber, into which the
rectum, genital, and urinary organs open; or, the anus isa

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 perineum.

These conditions of adult Vertebrata 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 Miillerian 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 anws, 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 Aves, 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,
where the bladder passes into it, by a peculiar gland, the pros-
tate. It thus becomes converted into what are termed the
Sundus, and neck of the bladder, with the prostatic and mem-
branous portions of the urethra. Concomitantly with these
changes, a process of the ventral wall of the cloaca makes its
appearance, and is the rudiment of the intromittent organ, or
penis. Peculiar erectile vascular tissue, developed within
this body, gives rise to the median corpus spongiosum and
the lateral corpora cavernosa. The penis gradually 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 ischia. The under, or pos-
terior, surface of the penis is, at first, simply grooved; by de-
zrees 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
frequently dilated into the so-called bulbus urethree, glands,
galled Cowper’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 definitive
urethra is finally formed.

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

MODIFICATIONS OF THE REPRODUCTIVE ORGANS. 99

dition of a process of the 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 the penial urethra and gen-
ito-urinary sinus are united into one tube, but the corpora
cavernosa are not directly attached to the ischium.

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

In the female sex, the homologue of a penis frequently
makes its appearance asa 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
Lemuride), 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 peritonzeum,
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 cremaster.
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 labia majora represent the scro-
tal, the labia 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 Verte-
brata. Among these may be reckoned the integumentary
pouches, in which the young are sheltered during their devel-
opment in the male Pipefish (Syngnathus), in some female
Amphibia (Notodelphys, Pipa), and Marsupialia ; together
with the mammary glands of the Mammalia.

CHAPTER IIT.
THE FROVINCHS OF THE VERTEBRATA—THE CLASS PISCES,

Tue Vertebrata are divisible into three primary groups or
provinces: the Lchthyopsida, the Sauropsida, and the Mam-
malia.

I.—The Ichthyopsida

1. Have the epidermic exoskeleton 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 vertebrz are dis-
tinct, their centra have no epiphyses.

3. The skull may be incomplete 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 only 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. .

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

|
|

THE SAUROPSIDA. 101

8. There are never fewer than two aortic arches in the
adult.

9. Respiration takes place by. branchiz 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
never 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 vertebrz 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 prodtic is always 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 always 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 Mam-
malia, but between the proximal and the distal divisions of
the tarsus.

6. The alimentary canal terminates in a cloaca.

%. 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 belongs to the right side.

9. Respiration is never effected by means of branchiz, 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
_ acomplete partition between the thoracic and the abdominal
viscera.

L102 THE ANATOMY OF VERTEBRATED ANIMALS.

11. The Wolffian 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.

16. There are no mammary glands.

IJ.—The Mammalia

1. Always possess an epidermic exoskeleton in the form of
hairs.

2. The vertebree are ossified, and (except in the ornitho-
delphia) their centra have terminal epiphyses.

3. All the segments of the brain-case are completely ossi-
fied. No distinct parasphenoid exists in the adult. The prodtic
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 with 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 auditis.

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

%. 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 branchiz, but,
after birth, is performed by lungs.

10. There is a complete diaphragm.

11. The Wolffian bodies are replaced 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.

ee)

THE CLASS PISCES. 103

14. The embryo has an amnion and allantois,
15. Mammary glands supply the young with nourishment,

The Ichthyopsida.—Class I.—PIisczs.

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 (supra, p.79 ), is highly charac-
teristic of Fishes, though these organs cannot be said to exist
in 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-
brata. The heart is a simple tube, and the liver is saccular. (Lepro-

carpia. Haeckel.)
I.—Pharyngobranchii.

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. (Pacuy-
carpIa. Hck.)

a. The nasal sac is single, and has a median external aperture. Neither
mandibles nor limb arches are developed. (Monorhina. Hck.)

Il.—Warsipobranchii.

b. There are two nasal sacs with separate apertures. Mandibles and
limb arches are developed. (Amphirhina. Hck.)
a. 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.

Il.—Hlasmobranchii.
8. Membrane bones are developed in relation with the skull.
1. The optic nerves form 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,

6, The nasal passages communicate with the oral cavity. There
are lungs, and the heart has two auricles.

VI—Dipnoi.

104 THE ANATOMY OF VERTEBRATED ANIMALS.

I. The PHaryncosrancuu.—tThis order contains but one
species of fish, the remarkable Lancelet, or Amphioxus lanceo-
latus, which lives in sand, at moderate depths in the sea, in
many parts of the 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
hes 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, f,g). 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.—Amphiorus lanceolatus.—a, mouth; 0, pharyngobranchial chamber; c, anus;
d, liver; ¢, abdominal pore.—B, the head enlarged; a, the notochord; 0, the represent-
atives of neural spines, or fin-rays; ¢, the jointed oralring; d, the filamentary append-
ages of the mouth; @, the ciliated lobes of the pharynx; /, g, part of the branchial sac;
h, the spinal cord.

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

THE PHARYNGOBRANCHI. 105

straight intestine, ending in the anal aperture, which is situ-
ated at the root of the tail at a little 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) isa saccular diverticulum of the
ntestine, the apex of which is turned forward.

— WT < = — :
Ch i TA i NT : ‘ TANCE Tp ae
ail ue HI Mi HAIN WU N

Wig. 29.—Anterior end of the body of Amphioxus.—Ch, notochord; My, myelon, or spinal
chord; @, position of olfactory (?) sac; 6, optic nerve; c¢, fifth (?) pair; d, spinal nerves;
é, representatives of neural spines, or fin-rays; 7, g, 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 which it possesses
in the earliest embryonic stage only, in other Vertebrata.
The blood brought back from the body and from the ali-

106 THE ANATOMY OF VERTEBRATED ANIMALS.

mentary canal enters a pulsatile cardiac trunk, which 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 pharynx the blood is poured, by the two anterior
trunks, and by the branchial veins which carry away the
aérated 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, 6). Neither is there a trace of any distinct skull, jaws,
or hyoidean apparatus; and, indeed, the neural chamber, which
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 myelon 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, 0, c).

According to M. Kowalewsky,* who has recently studied

* “Mémoires de l’Académie Impériale des Sciences de St. Petersburg,”
i867,

THE PHARYNGOBRANCHII. 107

the development of Amphioxus, 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 were, 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 acquires 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. Kowalewsky points out the resemblance, amounting almost
to identity, of the embryo at this stage with that of many
Invertebrata.

One face of the spheroidal blastoderm becomes flattened,
and gives rise to damince 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 pore 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 whicd grow over the bran-
chize 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
branchize and alimentary canal; and in the extension of the
notochord forward to the anterior end of the body—Amphi-
oxus differs 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 Pachycardia, comprising all other Verteorata,
The great peculiarities in the development of Amphiozus,
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 Amphioxus is known.

II, The Marsrpoprancui.—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 skull 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-

‘ ill tae :
t

|

SS
LSS]S=———

fia. 30.—A, the skull of a Lamprey, viewed from the side; B, from above :—a, the ethmovo-
merine plate; &, the olfactory capsule; ¢, the auditory capsule; d@, the neural arches of
the spinal column; e, the palatopterygoid portion; 7, probably, the metapterygoid, or
superior quadrate, portion, and g, the inferior quadrate portion, of the subocular areb; h,
stylohyal process; 7, lingual cartilage; x, inferior, / lateral, prolongation of the cranial
cartilage; 1, 2, 8, accessory labial cartilages; m, branchial skeleton. The spaces ov
either side of 1 are closed by menibrane.

THE MARSIPOBRANCHIL. 109

amn. There are no jaws; but the palatopterygoid, the quad-
rate, the hyomandibular, and the hyoidean apparatus of higher
Vertebrata, are imperfectly represented (Fig. 30, f, 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 Marsipobranchii 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 Vertebrata.

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 peritonzeum.

In Myzxine 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, with 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
cesophagus ana 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 Myzine 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 VERTEBRATED ANIMALS.

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

Fic. 81.—Side and upper views of the brain of Petromyzon Jlwwiatilis, 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 the
rhinencephalon (A); B, the prosencephalon; C, the thalamencephalon; D, 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; IL., the optic; III., the oculo-
motorius ; IY., the patheticus; V., the trigeminal; VI., the abducens ; VIL., the facial, and
the auditory; VIII., the glosso-pharyngeal and pneumogastric; IX.,the hypoglossal
nerves; 1, 1’, 2, 2’, sensory and motor roots of the first two spinal nerves. In the figure
of the membranous labyrinth: %, the auditory nerve; a, the vestibule; c¢, the two semi-
circular canals, which correspond with the anterior and posterior vertical canals of other
Vertebrata; d, their union and common opening into the vestibule; b, the ampulle.

blindly below and behind, but in the Hags (Myzine), it opens
into the pharynx. Inno other fishes, except Lepidosiren, does
the olfactory apparatus communicate with the cavity of the
mouth.

The reproductive organs of the Marsipobranchii are solid
plates suspended beneath the spinal column, and they have na

THE ELASMOBRANCHII. TEL

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

Fie %2.--Vertical and longitudinal section of the anterior part of the body of a Lamprey
\Petromizon marinus): A, the cranium with its contained brain; @, section of the
edge of the cartiluge marked a, in Fig. 30; O//, entrance into the olfactory chamber,
which is prolonged into the cecal pouch, 0; Ph, the pharynx; Pr, the branchial chan-
nel, with the inner apertures of the branchial sacs; J/, the cavity of the mouth, with its
horny teeth ; 2, the carvilage which supports the tongue; 3, the oral ring.

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

The Marsipobranchii 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 perishableness of
their bodies; though horny teeth, like those of the Lampreys,
might have been preserved under favorable circumstances.

III. The Erasmosrancuit.—This order contains the Sharks,
the Rays, and the Chimera.

The integument may be naked, and it never possesses scales
like those of ordinary fishes; but, very commonly, it is devel-
oped into papille, 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 exoskeleton ;”

112 THE ANATOMY OF VERTEBRATED 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-
ing, 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 Marsipobranchii, 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, lamella 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 wrostyle. 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
which 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 diphycercal (p. 21). The Monkfish
(Squatina) and many other Hlasmobranchit 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 Hlasmobranch 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 premaxillze nor maxille are present, the “ jaws”

THE ELASMOBRANCHIL 113

of an Elasmobranch 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 Chimera (Fig. 33), by the anterior
portion (B, DY) 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
movably articulated in front with the fore-part of the skull;
and, posteriorly, 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 (/) and with the mandibular or Meckelian cartilage
(dm). This cartilaginous suspensorium represents the hyo-

ae
oe

\

Vie. 33.—Vertical section of the skull of Chimcra monstrosa, without the labial and nasul]
cartilages: A, the basi-occipital region; P, the pituitary fossa; Va, partition between
the olfactory sacs; B, alveolus for the anterior upper-jaw tooth; C, D, the region of the
triangular cartilage which answers to the hyomandibular and quadrate; D, B, that
which answers to the quadrate, pterygoid, and palatine; J/n, the mandible; J O7, the
interorbital septum; asc and psc, the anterior and posterior semicircular canals; L., IL.,
Y., VIIL, exits of the olfactory, optic, fifth and eighth pairs of nerves.

mandibular and the symplectic bones of the TZeleoste?, and
gives attachment to the hyoidean apparatus (Hy). The lat.

114 THE 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 Hlasmobranchii, the apertures of the
gill-sacs are completely exposed. But in one group, the
Chimera, 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 Llasmobranchii. (Figs. 34 and
35, 7, &, L.)

The pectoral arch consists of a single cartilage on each
side. The two become closely 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 they are always numerous, and their crowns
are usually triangular and sharp, with or without serrations
and lateral cusps. Asa rule, the anterior teeth on each side
have more acute, the posterior more obtuse crowns. In the
Port Jackson shark (Cestracion), 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 Myliobates, the middle teeth have transversely-elongated,

115

THE ELASMOBRANCHII.

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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 VERTEBRATED ANIMALS.

Aetobatis only the middle transversely elongated teeth remain,
In the Sharks and Rays the teeth are developed from papilla,
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 Chimera.

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 Chimcera, 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 cesoph-
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 dilatas
tion separated from the stomach by a pyloric valve. This
duodenal segment of the intestine is usually known as the
Bursa Entiana. Mt 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 abdominal 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 ELASMCBRANCHII. 117

In a good many Hlasmobranchii there is a spiracle, or
aperture leading into the cavity of the mouth, on the upper
side of the head, in front of the suspensorium. From this
aperture (which, according to the observations of Prof. Wy-

Fig. 86.—The aortic bulb of a Shark (Zamna), laid open to show the three rows of valves,
v, v, ©, and the thick muscular wall, am.

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 Chz-
mera), or under-surface (Rays), of the neck, and, by internal
apertures, into the pharynx.

The anterior wall of the anterior sac is supported by 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 laminz; 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
interposed 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 aérated 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 Hlasmobranchii 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 restiformida) 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

iia. 37.—The brain of the Skate (Raia batis). A. From above; B. A portion of the ven:
tral aspect enlarged: s, the olfactory bulbs; @, the cerebral hemispheres which are nnited
in the middle line; %, the thalamencephalon; ¢, the mesencephalon; d, the cerebellum ;
aa, the plaited bands formed by the corpora restiformia; IL. II., 1V., V., the cerebral
nerves of the corresponding pairs; 7, the medulla oblongata; 2, a blood-vessel. In B. :
ch, the chiasma of the optic nerves; /, the pituitary body; 2 and »v, vessels connected
with it; %, the saceus vasculosus ; B, the pyramids of the medulla oblongata.

THE ELASMOBRANCSII. 119

ventricle, The third ventricle itself is a relatively wide and
short cavity, which sends a prolongation forward, on each side,
mto a large, single, transversely-elongated mass (Fig. 37, a),
which is usually regarded as the result of the coalescence of
the cerebral hemispheres, 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 differentiated. The large olfactory lobes are usually
prolonged into pedicles, which dilate into great ganglionic
masses where thev come into contact with the olfactory sacs
(Fig. 37, A.,s). The latter always 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 Vertebrata. The opticnerves fuse into a complete
chiasma (Fig. 37, B., ch), as in the higher Vertebrata. 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 somewliat 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 Chimera, the labyrinth is completely enclosed
in cartilage. In the Rays, the anterior and posterior “ semi-
circular ” canals are circular, and open by distinct narrow ducts
into the vestibular sac. In the other Hlasmobranchii 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 Vertebrata. 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.

£30 THE ANATOMY OF VERTEBRATED ANIMALS.

The eggs are very large, and comparatively few.

The Dogfishes, the Rays, and the Chimera, are oviparous,
and lay eggs, enclosed in hard, leathery cases; the others are
viviparous, and, in certain species of Mustelus (levis) 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
periphery 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 Hlasmobranchii are divided into two groups, the Holo-
cephali and the Plagiostomi.

In the Holocephali, the palato-quadrate and suspensorial
cartilages are united with one another and with the skull into
a continuous cartilaginous plate; the branchial clefts are coy-
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 differ in
structure from those of the Plagiostomi. 'This sub-order con-
tains the living Chimera and Callorhynchus, the extinct
Mesozoic Ldaphodon 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 usually numerous,

The Plagivstomi are again subdivided into the Sharks
(Selachit or Squali), 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 (aje), 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 Llasmobranchii 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 Mesozoie
rocks. In the Palaeozoic epoch, dermal defences and teeth of
Llasmobranchit abound in the Permian and Carboniferous

THE GANOIDEI. 12]

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

IV. The Ganorper.—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, Amia, Ac-
cipenser, Scapirhynchus, and Spatularia, 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 Hlasmobranchii, and others with the Téleostez,
Thus:

a. The buldus aorte is rhythmically contractile, and pro-
vided with several rows of valves, as in the Hlasmobranchit,

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

c. There is a well-developed spiral valve in the intestine,
as in the Hlasmobranchii, 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, which extends beyond
them, as in the Hlasmobranchii ; but their extremities project
freely beyond the edge of the septum which separates each
pair of branchial clefts, as in the Zéeleostei ; and, as in the
Teleoste?, they are covered by a bony operculum.

b. There is a large air-bladder connected by a permanently
open pneumatic duct with the cesophagus, as in many Téleoste?.

ce. Asin the Teleoste?, 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 EKlasmobranch, 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 ; Ama is covered with overlapping cycloid scales ; Lepi-
dosteus and Polypterus have solid, rhnomboidal, enamelled scales,

122 THE ANATOMY OF VERTEBRATED ANIMALS.

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

Fig. 38.—The brain of Lepidosteus semiradiatus. A. From above; B. From below: f,
the medulla oblongata; d, the cerebellum; ¢, the optic lobes of the mesencephalon; g,
the cerebral hemispheres; h, the pituitary bedy; ¢, the lobi inferiores. (Oh, the chias-
ma; I., olfactory; LI., 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 Spatwlaria,
Scapirhynchus, and Accipenser have a persistent notochord,
in the sheath of which mere cartilaginous rudiments of the
arches of vertebrae appear. The ribs, when present, are par-
tially ossified. Polypterus and Amia have fully ossified ver-
tebree, the centra of which are amphiccelous. Lepidosteus also
has fully-ossified vertebrae; 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 vertebre, or their cartilagi-
nous representatives, are united with one another, and with
the posterior part of the skull. And the cranium may consist
principally of cartilage, membrane bones being superadded ;
or the primordial cartilage may be largely superseded by bone,
as in the Zeleoste?.

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. 193

beak, which, 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
Texeostean fishes, are developed ; and, in that of its roof, ossi-
‘fications, which represent the parietals, frontals, and other
membrane bones of the Zeleostet, appear.

The framework of the jaws in Spatudaria is very similar
to that in the Hlasmobranchii. There is a partly cartilagi-
nous, and partly ossified, suspensorial cartilage (A, B, Fig. 39),
which gives attachment below, directly, to the hyoidean arch
(Hy), and, indirectly, to the jaws. The latter consist of a

~
~~

™

OS RRO SI Rel aE elon nn) Mi V) fe:
heer AAA y
Mn f EPs =A Z

Kia. 39.—Side-view of the skull of Spatularia, with the beak cut away, and the anterior
(asc), and posterior ( psc), semicircular canals exposed: Aw, auditory chamber; 07,
the orbit with the eye; N, the nasal sac; Hy, the hyoidean apparatus; £7, the repre-
sentatives of the branchiostegal rays; Op, operculum; J/n, mandible; A, B, suspenso-
rium; J, palato-quadrate cartilage; #, maxilla.

palato-quadrate cartilage ()) united by ligament with its fel-
low, and with the prefrontal region of the skull at / ; 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, B, corresponds with the hyomandibular, or
suspensorial, cartilage in the Sharks and Rays; YD, 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 (Op) is attached
to the hyomandibular; and a branchiostegal ray (Br) to the
more strictly hyoidean part of the skeleton of the second vis-
ceral arch; while a membrane bone (/) representing tha
maxilla, and another (J/n) the dentary, of the lower jaw in
Teleostet, are developed in connection with the palato-oaadrate
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 Spatularia,
and large dermal bones (£ A, Z) are united with them, to

Fre. 40.—The cartilaginous 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 vertebre; 0, 6, lateral winglike pro-
cesses; ¢, rostrum; Aw, position of the auditory organ; 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, B, of the epiotics; #, of the ethmoid; G, G, of the postfrontals;
H, H, of the prefrontals; C, C, the parietals; D, D, are the frontals, and ¥, F, the squa-
mosals; X, the anterior dermal scute; J, Z, and Z, Z, dermal ossifications connecting the
rectoral arch with the skull.

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

Fie. 41.—Side-view of the cartilaginous cranium of Accipenser: a, rostrum; b, nasal
chamber; O7, orbit; ¢, auditory region; d@, coalesced anterior vertebre; ¢, ribs; 7, g, A,
suspensorium ; *%, palato-maxillary apparatus; Jf, 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 Amia, the skull presents
not only membrane bones, but, in addition, basi-occipital, ex-
occipital, and prodtic ossifications of the primordial cartilage,
to which others may be added. The vomers are double, as in
the Amphibia (? Polypterus). The apparatus of the jaws has
become modified in accordance with the Teleostean type of

THE GANOIDEI. 125

structure. The suspensorium consists of two ossifications
united by a cartilaginous intermediate portion. The upper—
broad, and movably articulated with the periotic capsule—is
the hyomandibular ; 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 Lepidosteus, or more closely united
with it, as in the other genera.

In Lepidosteus and Amia,a strong and long membrane
bone, the preoperculum, 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 Lepidosteus. The proximal end of the man-
dibular cartilage ossifies, and becomes a distinct articulare. A
dentary element is added on the outer, and a splenial one
upon the inner side of the cartilage; and in Lepidosteus, 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 single jugular plate is developed between the rami of the
mandible in Ama, and there are two such plates in Polypterus,
which may possibly represent branchiostegal rays.

In Accipenser, Spatularia, and Amia, the pectoral arch
presents two constituents: one, internal and cartilaginous,
answers to the cartilaginous pectoral arch of the Elasmo-
branchit, and to the scapula and coracoid of the higher Ver-
tebrata ; the other, external, consists of membrane bones rep-
resenting the clavicular, supra-clavicular, and post-clavicular
bones of the Zéleostet. 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 Polypterus comes
nearest to the Hlasmobranchii 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
scaly integument is continued to the bases of the fin-rays,

L126 THE ANATOMY OF VERTEBRATED ANIMALS.

which thus seem to fringe a lobe of the integument. Hence
the fin is said to be lobate. 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 Ganotdei are intermediate between the
Elasmobranchit and the Zeleostet.

In certain Ganoids, as Lepidosteus, 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 Accipenser and Polypterus,

\» i * es spiracula, or openings which com-

x £7 municate with the mouth, lie on the

top of the head, in front of the sus-

pensorium, as in many Elasmo-
branchs.

Lepidosteus, Accipenser, and Sca-
pirhynchus, have branchie attached
to the hyoidean arch, as in the Elas-
mobranchit. ‘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 cesophagus. 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
Fic. 42—The female reproductive male and female reproductive organs

preans of Amia calea: % are. (continuous wath. those *podies:

the open ends of the genital ‘
ag Oe Boone and each duct opens into the dilated
ig e . °4 ;
urinary bladder; e, ¢, the open- ureter of its side. In the other Ga-
mgs of the ureters into the blad- noids the proximal ends of the gem.
der; 7, the anus; g, g, the ab- é .
dominal pores; /, the urogenital tal ducts, in both sexes, open widely
ab ar into the abdominal cavity. In Po-
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 GANOIDEL. 127

When the fossil, as well as the existing Ganoidet, are
taken into account, they form a large order, divisible into the
following sub-orders: 1 Amiadc, 2. Lepidosteide, 3. Crosso-
prerygidce, 4, Chondrosteide, all of which have living repre-
sentatives ; while the other three—viz., 5. Cephalaspide, 6.
Placodermi, and 77. Acanthodide—have been extinct since
the Palzeozoic epoch, and are only ranged among the Ganoids
provisionally, inasmuch as we have no knowledge of their in-
ternal anatomy.

1. The Amiade have a single living representative in the
rivers of North America—Amia 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 Lepidosteide 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 Lepidosteus ; in the Mesozoic rocks, by a great variety of
genera— Lepidotus, Gchmodus, Dapedius, etc.; and, in the
Paleozoic epoch, by Paleoniseus in the Carboniferous, and
probably by Chetrolepis, in the Devonian, formation.

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

NY ae
*) R an

Fic. 43.—Restoration of Holoptychius.

rhomboid. The dorsal fins are either two in number, or, if
single, very long, or multifid. The pectoral fins, and usuall ly
the ventrals, are lobate; they are sometimes rounded, as in
Pol, lyptcrus—sometimes oreatly elongated and almost filiform,
as in Holoptychius (Fig. 43). There are no branchiostegal
rays, Lvt two principal, and sometimes many smaller lateral,

128 THE ANATOMY OF VERTEBRATED ANIMALS.

jugular plates. The tail may be either diphycercal or hetero-
cercal.

The only living representatives of this sub-order are Polyp-
terus and Calamoichthys, which inhabit the rivers of North
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 Celacanthini, 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 Celacanthini also
occur in the Carboniferous formation ; and the great majority
of the Crossopterygide are found in this and the Devonian
formations ( Osteolepis, Diplopterus, Glyptolemus, Megalich-
thys, Holoptychius, Rhizodus, Dipterus, 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 Crossopterygide
that the Ganoids are especially connected with the Dipnoi,
and, through them, with the Amphibia.

4, The Chondrosteide are either naked, or have derma!
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 tailis heterocercal. There are no cartilage-bones in
the brain-case. The teeth are very small, or absent.

The Sturgeons (Accipenser)—which inhabit the northern
rivers of Europe, Asia, and America, occasionally migrating
to the sea—Spatularia, and Scapirhynchus (found in the rivers
of North America), are the recent members of this group,
which is represented, in the older Mesozoic rocks, by Chon-
drosteus.

5. The Cephalaspide are remarkable fishes, probably allied
to the Chondrosteide, 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 Cephalaspis ; the body is covered with flat bony
scales or plates, and possesses two large pectoral fins. The
characters of the body and fins of Péterapsis 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

laspide would approach the Marsipobranchii more nearly than
any of the other amphirhine fishes do.

6. The Placodermi, comprising the genera Coccosteus,
Prterichthys, 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 region was covered with small
scales in Pterichthys, while in Coccosteus it appears to have
been naked. The pectoral member of Pterichthys 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., Clarias)
in their form and arrangement, and it seems probable that the
Placodermi were annectent forms between the physostome
Teleostet and the Ganoidei.

7. The Acanthodide, on the other hand, seem to have con:
nected the Ganoidei with the Hlasmobranchii. 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 H'lasmobranchii, 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 asingle bony hoop.

The Pycnodontide, 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
vertebre. The skull is high and narrow, as in Balistes ; the
premaxillz are small, and there are no teeth in the maxille,
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, which are also
armed with 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 VERTEBRATED ANIMALS.

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

The remains of Ganoid fishes began to appear in the Upper
Silurian rocks at the same time as those of the /’lasmobranchit,
with which they constitute the oldest Vertebrata Fauna; they
abound in the Devonian formation, and constitute, with the
Elasmobranchii, the whole of the Paleozoic Fish Fauna.
We are in ignorance of the true affinities of Z’harsis and
Thrissops, and of the Hoplopleuride ; but unless some, or all,
of these are Teleosteans, Ganoids and Hlasmobranchs, alone,
constitute the Fish Fauna of the Mesozoic formations, as far
as the bottom of the Cretaceous series.

V. The Tretzosrre1.—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-
ction), the body may be encased in a complete cuirass, which is
calcified, but has not the structure of bone. Again, as in the
Filefishes (Balistes), 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 exhibit the la-
cunz 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 vertebrz are usually bi-
concave, each face presenting a deep conical hollow. In cer-
tain Eels (Symbranchus), the centra of most of the vertebrz
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 together,
and with the skull, into one mass, as in the Ganoids.

The vertebrz 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

tebree 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 the
vertebree, 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 preéxist-
ing cartilages, and lie between, and are connected with, the
spines of the vertebrae. The fin-rays may be entire and com-
pletely ossified, or they may be transversely jointed and lon-
gitudinally subdivided at their extremities. Not unfrequently,
the articulation between the fin-rays and the interspinous bone
is effected 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 vertebree. Sometimes, as in the Sal-
mon (lig. 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 body, interspinous bones are
developed between the spines of the inferior arches of the ver-

132 THE ANATOMY OF VERTEBRATED ANIMALS.

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

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

fats. See 5} yey! mE,

‘ AS. BS Pro,

Fic. 44.—The cartilaginous cranium of the Pike (Zsoa lucius), with its intrinsic ossifica-
tions; viewed, A, from above; B, from below; ©, from the left side: 2, V7, nasai fosse;
I. Or, interorbital septum; @, groove for the median ridge of the parasphenoid ; 0, canal
for the orbital muscles. Sq., wrongly so marked, is the Fterotic. V.and VIII. mark
the exits of the fifth and pneumogastric nerves; 3, 8, small ossifications of the rostrum.

fish, and only becomes partially ossified; in other cases it al-
most disappears. A basi-occipital (B. O.), ex-occipital (#2. 0.),
and supra-occipital (S. O.) bone are developed in it, and form a
complete occipital segment. The proper basi-sphenoid (BS)
bone is always a very small, and usually somewhat Y-shaped,
bone. The alisphenoids (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 anterior moiety of
the cranial cavity is consequently re-
duced to a comparatively narrow pas-
sage above the septum (Hig. 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 some-
times, as in the Pike, ossification ma
take place init. (Fig. 44, 3,3.) The
antorbital, or lateral ethmoidal, pro-
cesses of the primordial cranium os-
sify, and give rise to the prefrontal
bones (Prf.). The postorbital pro-
cesses also ossify as postfrontals (Pt7.).
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 (Zp. O.), 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 pterotic 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 proétic (Pr. 0.) is always a well-
developed bone, and occupies its regu- 5... 4s “ade lbidiial and ae
lar place, in front of the anterior Ver- tical section of a fresh Pike's
tical semicircular canal, and behind the fii ania Bere rC,
exit of the trigeminal nerve. and P.V.C., read 4.8.¢., an-
In addition to these cartilage peat aca ae
bones, the brain-case of osseous fishes _—Parasphenoid; y, the bast

: gs sphenoid; Vo, the vomer
is additionally defended by numer- _P, the pituitary fossa.

AWN ET STINTS

RI

ANH

rritrers “
Ss ee
Vo.

\

134 THE ANATOMY OF VERTEBRATED ANIMALS.

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

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

2 The large frontals (#7.), which may or may not unite
into one.

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

IW
amit - 7 or ! Saad ~ A j
Vo. Prss. Zy ae ng Sia

Fra. 46.—Side and upper views of the skull of a Pike (Zsox lucius), without the facial or
supra-orbital bones: y, the basisphenoid; 2, the alisphenoid; a, the articular facet for
the hyomandibular bone.

The under-surface of the skull possesses two membrane
bones: in front the vomer ( Vo.), and, behind, the huge para-
sphenoid (a, x), 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 (Pmz.) are attached, sometimes closely, sometimes
loosely, to the anterior extremity of the cranium; and behind
these are the maxillz (J/x.), 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 maxillz take little
or no share in the formation of the gape, which is bounded
above by the backwardly-extended premaxille.

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

THE TELEOSTEI. 135

Amia. The homologue of the suspensorium of the Alasmo-
branchii is articulated with a surface furnished to it by the
postfrontal, pterotic, and prodtic bones. Usually it moves

Ar

Fia. 47.—Side-view of the skull of a Pike (Zsox lucius): Prf, prefrontal; ZH. 1., hyoman-
dibular bone; Op, operculum; S.Op., suboperculum; J.O0p, interoperculum; Pr. Op,
preoperculum; 4rg, branchiostegal rays; Sy, symplectic; J/¢, metapterygoid; Pi,

alato-pterygoid arch; Qu, quadrate bone; A7, articular; Amn, angular; DY, dentary;
.O7r, suborbital bone.

freely upon that surface, but, in the Plectognathi, it may be
fixed. It ossifies so as to give rise to two bones: an upper
broad hyomandibular (HZ. M.), with which the operculum artic-

_ Fie. 48,—Pslato-quadrate arch, with the hyomandibular and symplectic of the Pike, viewea

from the inner side; the articular piece (A7t), of the lower jaw, and Meckel’s cartilage
(Wck.) of the Pike; seen from the inner side: @, the cartilage interposed between the
hyomandibular (7.J/,), and the symplectic (Sy.); 0, that which serves as a pedicle to
the pterygo-palatine arch; ¢, process of the hyomandibular with which the operculum
articulates ; d, head of the hyomandibular which articulates with the skull.

ulates; and a lower styliform symplectic (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 (£7.) in front, and

136 THE ANATOMY OF VERTEBRATED ANIMALS.

the quadrate (@Qu.) behind and below. Besides these there
may be three others: an external, ectopterygoid (Zcpt.), an
internal, entopterygoid (Hpt.), and a metapterygoid (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 ((Wck.) persists throughout life, but the
ossification of its proximal end gives rise to an 0s 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 (wrohyal) extends back to join the median
elements of the branchial apparatus. The cornua themselves
are usually ossified into four pieces: an upper (epihyal) and a
lower (ceratohyal) large ossification, and two small ones (basi-
hyals) 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
hypopharyngeal 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 preoperculum (P. Op.), oper-
culum (Op.), and branchiostegal rays (Br.), already met with
among the Ganoidei, are the most constant of these. Beneath
the operculum, lies a swhboperculum (S.Op.), and below this
an interoperculum (I. 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
livamentous, as in the Siluroids.

The branchiostegal rays are attached partly to the inner,
and partly to the outer, surface of the hyoidean arch, They
support a membrane, the branchiostegal membrane, which
serves as a sort of inner gill-cover.

THE TELEOSTEL. 137

Most Téleostet 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 Murcenophis.
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 (thoracic), or even in front of them (jugular).
In the asymmetrical Plewronectide one pectoral fin may be
larger than the other, or may alone remain, as in Monochirus.

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

Fra. 49.—The bones of the pectoral arch and fore-limb of the Pike (Hsom Jucius): A, a
semi-diagrammatic view of these bones, to show their relative natural position. The
clavicle (C7) is supposed to be transparent. S.cl, supra-clavicula; p.cl, post-clavicula:
ce, d, the posterior and anterior ends of the outer margin of the scapulo-coracoid.—B, the
scapulo-coracoid and limb separate and on a larger scale; Scp, scapula; (7, coracoid;
@, basal cartilages; 0, fin-rays; c, corresponds with c in the foregoing figure.

138 THE ANATOMY 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 post-clavicula (p.cl.).

Attached to the dorsal end of the clavicle, there is usually
a second much smaller bone, the supra-clavicula (S.cl.), and
this is very generally connected with the skull by a superficial
membrane bone, the post-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 mesopterygial 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 vertically. 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 premaxille of Sargus, where
they curiously simulate the form of human incisors ; and, im-
bedded in the coalesced hypopharyngeal bones, in Labrus.

3. Isolated teeth, imbedded in the substance of the bone
which supports them, The teeth and the supporting bone
wear away in front, and are replaced by new teeth developed
behind the others. This structure is seen in the coalesced
hypopharyngeal bones of the Parrotfish (Scarus).

THE THLEOSTEI. 139

4, Beak-like compound teeth, attached to the premaxilla
and dentary bones of the mandible.

These are of two kinds. In the Parrotfish (Scarus) the
beak is formed by the union of numerous separately-developed
teeth into one mass. But in the Gymnodonts (Zetrodon and
Diodon) the beak is produced by the coalescence of broad
calcified horizontal lamellz 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 Scomberesoces, 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 cxcal diverticula, the pyloric cceca.
The small intestine has no spiral valve, though the mucous
membrane 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 cesophagus, or even with the stom-
ach, as in the Herring. In other Zéleostei, the air-bladder oc-
cupies the 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 Blennii, the Pleuronectide or Flatfishes,.
the Sand-eel (Ammodytes), the Loricarini, and Symbranchii,
and some members of other families—there is no air-bladder.
In those Ze/eostet in which it is present, it may be divided into
two parts by a constriction ; or it may be prolonged into di-
verticula; or retia mirabilia may be developed in its walls.
Sometimes the air-bladder is brought 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, Cypri-
novdei, and Characini, 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 cesophageal
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 bulbus aorte, 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 toward 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, which passes forward under
the base of the skull; and this is united with its fellow by a
transverse branch—so that a complete arterial circle, the cir-
culus 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 mirabile, which lies in the inner side of the hyo-
mandibular bone, and sometimes has the form of a gill. This
is the pseudobranchia. The branches of the rete mirabile
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, the respiratory organs
are pouches, the anterior and posterior walls of which are
raised into vascular folds. The walls of adjacent pouches are
distinct and but loosely connected together ; and considerable
spaces of integument separate their rounded outer apertures.

In the ordinary Hlasmobranchit, 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 walls of
successive pouches are more closely approximated, so that they
are divided only by septa; but the vascular plaits of the sur

THE TELEOSTEI. 141

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

In Chimera, 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
eonsequently free.

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

The Zeleostei have no functional hyoidean, 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, Cyclopterus, 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, Diodon). In Mal-
thea the number is reduced to five, only the anterior series of
the third arch being developed; and in Amphipnous 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. ‘bese may take the form of arborescent appendages to
the upper ends of some of the branchial arches, as in Clarias,
Heterobranchus, and Heterotis ; 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 chanos), an accessory gill may be developed
in acurved cecal prolongation of the branchial cavity. Final-
ly, in Saccobranchus singio and in Amphipnous cuchia, the
membrane lining the branchial chamber is prolonged into sacs,
which lie at the sides of the body, and receive the blood from
the divisions of the cardiac aorta which supply the branchiz,
while they return it into the dorsal aorta.

All these fishes (except Zutodeira) 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 ANIWALS.

The kidneys of Teleostean fishes receive a great part of
their blood from the caudal vein, which ramifies inthem. They
vary greatly in length, sometimes extending along the whole
under-surface 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 Ye/eostei 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-
f___.cephalon, which has a pair of inferior
2B ~ enlargements, lobi 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
ie at to the valve of Vieussens in mammals,

}\ HAN is thrown forward into a deep fold
jh iil \ which lies above the crura cerebri,
Ey nes ape pike view. 2Hd divides (the wera tertio ad quar-
ed from above: A, the olfactory tum ventriculum from the ventricle
eee aie opie cecveas B the of the optic lobes throughout almost
cerebral hemispheres; @ the the whole extent of the latter. This
optic lobes; P, the cerebellum. F414 is the “fornix” of Gottsche. On
each side of it the floor of the ventricle of the optic 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 Vertebrata.

Hach 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 (Amblyopsis speleus), 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-

THE TELEOSTEI. 143

titating membrane, but immovable external eyelids may be
developed. The choroidal gland, mentioned above, surrounds
the optic nerve between the sclerotic and the choroid. Very
generally, a 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 fishes,
the lens is spheroidal, and the cornea flat. The sacculus of the
auditory organ contains large solid 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 either 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 TZeéleostet are ovoviviparous (e. g., Zoarces vi-
viparus), the eggs being retained in the interior of the ovary,
and hatched there. In the male Syngnathus, and other Lo-
phobranchit, 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 with external gills, nor
with spiracula.

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

1. The Physostom?.—This group contains the Siluroidet,
the Cyprinoidei, the Characini, the Cyprinodontes, the Sal-
monide, the Scopelini, the Hsocini, the Mormyri, the Galax-
te, the Clupeide, the Heteropygii, the Murcwnoidei, Sym-
branchii, and Gymnotini. The air-bladder is almost always
present, and, when it exists, has an open pneumaticduct. 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 St/urotdei) 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 Anacanthini.—The body has cycloid or ctenoid

144 THE ANATOMY OF VERTEBRATED ANIMALS.

scales, oris naked, The ventral fins, if present, are jugular in
position, The fin-raysare all articulated. The inferior pharyn-
geal bones are distinct. ( Ophidint, Gadoidei, Pleuronectide.)

The Pleuronectide 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 jugular ventral fins, entire fin-rays in some of the fins, and
distinct inferior pharyngeal bones. The Percoidei, Cata-
phracti, Sparoidei, Sciceenoidei, Labyrinthici, Mugiloidei, No-
tacanthini, Scomberoidei, Squamipennes, Tenioidei, Gobioi-
dei, Blennioidei, Pediculati, Theuthyes, and Histulares, be-
Icng to this great group.

4, The Pharyngognathi is the name given by Miller 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
eycloid 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, Pomacentridw, Chro-
mide ; or articulated, as in the Scomberesoces.

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 Lophobranchii.—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. (Pegaside, Syngnathide.)

6. The Plectognathi.—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-
maxillz and, usually, the hyomandibular, are immovably united
with the skull—a character of rare occurrence among other
fishes. (Gymnodontide, Ostraciontide, Balistide.)

The greater number of Zeleostei are marine. No Anacan-
thini, Plectognathi, or Lophobranchii, and only one family of
Pharyngognathi (the Chromide), inhabit completely fresh
water. Comparatively few Acanthopteri are fluviatile. On
the other hand, by far the greater number of the Physostomé
are, either temporarily or permanently, fresh-water fish.

If the Leptolepide (Thrissops, Leptolepis, Tharsis) are

|

THE DIPNOL. 145

Ganoids, the Zéleostei are not known before the Cretaceous
epoch, when both Physostomt and Acanthoptert make their
appearance, under forms, some of which (e. g., Beryx) are
generically identical with fish living at the present day.

VI. The Drenor.—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,

\ oS A
eg

in

\\

he

DM,

Fra. 52.—Skull of Lepidosiren annectens: A, the varieto-frontal bone; B, the supra-orbi-
tal; C, the nasal; D, the palato-pterygoid; #, tne vomerine teetn; £, O., the ex-occipi-
tal; Jf, the mandible; Hy, the hyoid; 4r, the branchisstegal rays; Op, the pete
plate; «, the parasphenoid ; y, the pharyngo-branchial; Or, the orbit; Aw, the auditory
chamber; JV, the nasal sac,

146 THE ANATOMY OF VERTEBRATED ANIMALS.

The spinal column consists of a thick notochord, invested
by a cartilaginous sheath, without any 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-rays support the median fin. The skull, the palato-
quadrate, and suspensorial apparatus, form, as in Chimera,
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

£. 0.) in the side-walls of the cranium. <A large parasphenoid
x) underlies the base of the skull. Upon its roofa great single
bone (4), 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

Fig. 53.—Longitudinal and vertical section of the skull of Lepidosiren. The cartilage ia
dotted; the membranous and bony constituents are shaded with lines. A, B, C, D, Z,
Hy, as in the preceding figure; x, 7, the parasphenoid; P, S1, cartilaginous presphenoi-
dal region; ch, notochord; Aw, situation of auditory chamber; 1, 2, first and second
vertebre; J7., V., VIII, exits of optic, trigeminal, and vagus nerves; a, q uadrato-
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
iongitudinally 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 (JY) extends from
the middle line along the upper and the under surface of the

THE DIPNOI. 144

palato-quadrate arch on each side to near the articular 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 hyoi-
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 (Br, Fig. 52).

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 aérated 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 branchiz; 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 aremarkable circumstance that, while the Dipnoz 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 IV.
THE CLASS AMPHIBIA.

Tur IcurHyorsipa.—Class I.—Ampuieia.

The only clearly diagnostic characters of this class as coms
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 Vertebrata.

Certain other structural 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 Amphibia, they
are concealed within the skin ( Cecilia, Ephippifer). In the
extinct Labyrinthodonta, 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
Menopoma.

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 vertebrae amphicelous or opiz-
thoccelous; the proximai elements of the tarsus not elongated.
A. Two or four limbs ; no scutes or scales,

I. Saurobatrachia or Urodela.

a. External branchie or gill-clefts persistent, or disappearing
only in advanced age; no eyelids ; vertebre amphiccelous;
carpus and tarsus cartilaginous.

150 THE ANATOMY OF VERTEBRATED ANIMALS.

1. Proteidea.

6. No branchiz or branchial clefts in the adult ; eyelids present;
carpus and tarsus more or less ossified; vertebrae commonly
opisthoccelous,

2. Salamandridea.

BL. Limbs absent, or al] four present. Three large pectoral osseous
plates and an armor of small scutes on the ventral surface
of the body; vertebre amphiccelous; walls of the teeth more
or less folded.

IL. “Labyrinthodonta.
B. Tail obsolete in the adult.

A, Limbs absent; numerous minute dermal scutes imbedded in

the integument of the serpentiform body.
Til. Gymnophiona,

B. Ail 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

IV. Batrachia or Anura.

The integument in most Amphibia is soft and moist, as in
the Frog, where numerous glands open upon its surface. The
Gymnophiona are exceptional, among existing Amphibia,
in possessing small, rounded, flexible scales, like the cycloid
scales of fishes, imbedded within the wrinkled integument.

In certain Batrachia (Ceratophrys dorsata, Ephippifer
aurantiacus), 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 which 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 median 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 surfazes 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, Micropholis. I have not met
with dermal ossicles in this position in other Labyrinthodonts.

THE AMPHIBIA. 151

But in Archegosaurus, Pholidogaster, Urocordylus, Kerater-
peton, Ophiderpeton, Ichthyerpeton, the integument between
the thoracic plates and the 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 Amphibia is least complete in

Archegosaurus, where the centra of the vertebre are repre-
sented only by bony rings, the ribs and the neural arches
being well ossified. In other Labyrinthodonts of the same
(Carboniferous) epoch, however, such as Anthracosaurus, the
centra of the vertebrz are completely ossified biconcave disks,
very like the centra of the vertebrae of Jchthyosaurus.
* In the existing Proteidea, and in the Gymnophiona, the
vertebral centra are amphiccelous. In the Salamandridea
they are opisthocelous. In Pipa and Bombinator they are
also opisthoccelous, but in other Batrachia they are, for the
most part, proccelous, 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 speciaily 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 Saurobatrachia, and the Laby-
rinthodonta, the number of the vertebrz in the trunk is con-
siderable, and the members of the two latter groups have long
tails. Butin the Batrachia, the total number of vertebrze
does not exceed eleven, of which eight belong to the presacral
region, one to the sacrum, and two (modified vertebrz) to the
coccygeal region. The transverse processes of some of the
presacral vertebrae are usually very long, but there are no
separately 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 Zeleostet ; 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 provtic ossification appears
to be very 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

4 ?s
SAM x
evi ee f
BR 1" be i:
Re ia ) f\
\4 bab" ‘
a
‘a 2 Ay
oi, Ns
‘

:
Eo.

Fia. 54.—The cartilaginous cranium of Rana esculenta. A, from above; B, from below;
y, the “os en ceinture,” 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

Ss

THE AMPHIBIAN SKULL. 153

other Vertebrata. Turbinal ossifications are developed in the
cartilage bounding the nasal capsules in some Amphibia.

Pua

Fig. 55.—Skull of Rana esculenta. A, from above; B, from below; C, from the left side
#, parasphenoid ; y, girdle-bone; Z, the “ temporo-mastoid.”

The membrane bones of the Amphibian skull are: 1. Front-
als and parietals, which, in the Batrachia, 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 Zeleostei and Ganoidet.
5. A membrane bone (Z), called “ temporo-mastoid ” by Du-
gés, 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 Vertebrata, in its lower
part to those of the bone /’ in Lepidosiren, to the preopercu-
lum of fishes, and to the tympanic of the higher Vertebrata.

Two premaxille are always developed. The maxille are
usually present, and may be connected, as in most Batrachia,
by quadrato-jugal ossifications with the outer side of the end
of the suspensorium, in which an ossification representing the

154 THE ANATOMY OF VERTEBRATED ANIMALS.

yuadrate bone is often developed. But the quadrato-jugals
(and even the maxillz) may be represented simply by more or
less ligamentous fibrous tissue, as is the case in the Urodela.
Pterygoid bones are developed in all Amphibia, and distinct
palatine bones in most, but not all, of the Batrachia, '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 Batrachia slopes greatly
backward ; and it undergoes the same modifications in direc-
tion, during the progress of any of the Latrachia 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 Batrachia.
The membrane-bones of the mandible are a dentary and a
splenial piece, with perhaps an angular element.

The hyoidean arch is, in most Amphibia, 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 Proteidea. In the Batrachia
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 which 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 Batrachia, the branchial arches disappear in the
adult; but in the Gymnophéona 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
Cecilia, and three of these are permanent.

Some peculiarities exhibited by the skulls of the Gymmno-
phiona, and by the Labyrinthodonta, are worthy of especial
notice.

In the former, e. g., in Ichthyophis glutinosa, the skull is
covered by 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 ta

THE LIMBS OF AMPHUIBIA. 155

answer to the bone (2) of the Frog, and to its quadrato-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 nasi. Another bone nearly encircles
the orbit, and, as a supra- and postorbital bone, has no ana-
logue among existing Amphibia. The palatine bones sur-
round the posterior and outer margins of the posterior nares,
und then extend baclt on the inner side of the maxilla, in a
manner unlike any thing observed among other existing Am-
phibia. But in the Labyrinthodonta, both this disposition
of the palatine and the complete roofing over of the skull by
bone are repeated, and there is a postorbital bone.

wT ————— —S- =
WYNUIY VN Nh SSS

AY \j i") V y WWW VWs
Jt,

vw

Ms lo

i AEARAALIAMAE MZ
N AARARAALAARAASEARAAAMRBLLEABELEEST TE
AAK \AK NS ——

=
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i.

Pmt SS

Fic. 56.—Side and upper views of the skull of Trematosawrus. 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 Ganoide?. In many Labyrinthodonts
the articular element of the lower jaw is completely ossified.

Archegosaurus possessed branchial arches when young,

156 THE ANATOMY OF VERTEBRATED ANIMALS.

and there can be little doubt that the other Labyrinthodonts
resembled it in this respect.

The limbs and their arches are completely absent in the
Gymnophiona, 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 posterior 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 Urodela 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 Salamandridea, 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 Batrachia, 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 omosternum (Fig. 57, o.st.). Behind, the coras
coids articulate with a well-developed sternum (s¢.). Distinct
ossifications arising on either side of the glenoidal cavity rep-
resent the scapula (sc.) 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 or fontanelle into a proper coracoid (e7.), 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 Protews. The pubis does not ap-
pear to be regularly represented by a distinct ossification, In
the Batrachia the applied flat faces of the expanded ventral
divisions of the pelvic arch coalesce into a disk.

Or

THE LIMBS OF AMPHIBIA. 157

In the genus Amphiuma, the limbs have each either two
or three digits. In Siren, the anterior limbs, which alone
exist, are three- or four-toed. In Proteus, the anterior limbs

Fig. 57.—The sternum and pectoral arches of a Frog, seen from above. The left supra-
scapula is removed: sc., scapula; 8.8¢., Supra-scapula; 7.8¢., prescapular process ; ¢7.,
coracoid; e.cr., epicoracoid; c7.f, coracoid fontanelle. The bar which bounds this in
front is the precoracoid, and bears the clavicle: o0.st., omosternum ; s¢., sternum; @.s?.,
xiphisternum.

are tridactyle, the posterior didactyle. Menobranchus has
tetradactyle feet, while in the other Urodela the anterior limbs
are tetradactyle, the posterior pentadactyle. The Batrachia
have four digits, with or without a rudiment of another, in the
fore-limb, and five in the hind-limb. In the perennibranchiate
Urodela, 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 Batrachia, they are for the most
part ossified.

In the Batrachia, the posterior limbs 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 two 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

[58 THE ANATOMY OF VERTEBRATED ANIMALS.

son with the size of the body. In the genera Archegosaurus,
Keraterpeton, Urocordylus, Lepterpeton, each foot possessed
five digits, and the carpus and tarsus were unossified.

The Amphibia usually possess teeth on the vomers, pre-
maxillz, maxille, 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 larvee of the Batrachia, and in Siren, the premaxillze 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; JMenobranchus and
Siredon have pterygoid teeth. Many of the Labyrinthodonts
possess palatine teeth. In some Gymnophiona 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 Amphibia 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
Ganoideit. In many of the Labyrinthodonts, again, two of
the anterior mandibular teeth take on the form of long tusks,
which are received into fossee, or foramina, of the upper jaw,
as in most existing Crocodilia. 'The tongue is fixed to the
floor of the mouth in Urodela and Gymnophiona, and remains
undeveloped in the genera Pipa and Dactylethra, which have
thence been termed Aglossa. In other Batrachia, 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 Batrachia 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 larvze (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

bulbus 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, Menobran-
chus, and Siren, the septum of the auricles is less complete
than in the other Amphibia, 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. Valves 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
off 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 two 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, which ascend upon the branchial
arches. The two anterior pairs of aortic trunks pass directly
into the roots of the 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 (v1.) gives off the
pulmonary arteries, the three next (V., Iv., UI.) supply the ex-
ternal branchize; and the anterior trunk passes, above, intv an
artery which divides into hyoidean and carotid branches.

In Salamandra 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 Botalli, The fourth
trunk gives off the pulmonary artery; some twigs for the
cesophagus, and a few cardiac branches, next arise from it;

160 THE ANATOMY OF VERTEBRATED ANIMALS.

and it then 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 Salamandra, in a ca-
rotid gland and ductus Botalli ; carotid, hyoidean, and oral
branches being given off from the former. The hindermosé,
or pulino-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 cceliaco-
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 isa valvular fold open toward the hear

THE RESPIRATORY ORGANS OF AMPHIBIA. 161

in each 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 gradually

Fie. 58.—The Axolotl (Siredor).

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
m the carotid passages. Hence the latter fill, and send arteri-
alized blood to the head.

The organs of respiration of the Amphibia, in the adult

162 THE ANATOMY OF VERTEBRATED ANIMALS.

state, are either external branchiw, combined with lungs, as
in the perennibranchiate Urodela; or lungs only, as in the
other Urodela, the Batrachia, the Gymnophiona, and, prob-
ably, the majority of the Labyrinthodonta.

In the perennibranchiate Urodela, 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 Amphiwma) 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 Batrachia
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 cesophagus, opens into a
short laryngo-tracheal chamber with which two
pulmonary sacs are connected, either directly,
or by the intermediation of bronchi (as in the
Aglossa), or by a trachea (as in the Gymno-
4 ,. phiona). The walls of the pulmonary sacs
j~ “are more or less sacculated. In most Asm-
phibia the lungs are equal in size; but in the
! snake-like Gymnophiona, the right is much

f smaller than the left. In Proteus, the pul-
monary blood is not all returned to the heart,
=) *™ some of it entering the veins of the trunk.

ad | i Aérial respiration is effected, in the Amphibia,

wi. by pumping the air from the oral cavity into

Eig. 50 The brain of the lungs. To this end the mouth is kept
Rana esculenta, =

from, above, magni- Shut, and ingress and egress to the air is given

ee wicte tain? by the nasal passages, which always open
or olfactory lobes, immediately behind the vomers, at the anterior
with, J., the olfac- y 4

tory nerves: He, part of theroofof the mouth, These passages

spheres: ho ths being open, and the hyoidean apparatus de-
thalamencephalon pressed, the air fills the cavity of the mouth.
ea oe am The external nostrils are then shut, and, the

. ’ . . . . .
ome age ; & ae hyoidean apparatus being raised, the air is
ellum; S. 7., the aie
fourth ventricle; forced, through the open glottis, into the lungs.

iMo., medulla oblen- hy ‘
ao All Amphibia possess a urinary bladder,

THE RESPIRATORY ORGANS OF AMPHIBIA, 163

which opens into the cloaca, and does not receive the ureters.
The kidneys of the Amphibia appear, like those of fishes, to
be persistent Wolffian bodies. _

In the brain of the Amphibia the cerebellum is always
very small, and represented by a mere band; the cerebral
hemispheres are elongated, and contain ventricles. In Proteus
the mesencephalon is very indistinctly marked. The optic
nerves form a chiasma.

As in fishes, the pneumogastric gives off a lateral nerve,
which runs along the sides of the body.

The eyes are very small, and covered by the integument,
in Proéeus, the Gymnophiona, and the genus Pipa, The
perennibranchiate and derotreme Urodela have no eyelids;
but most Batrachia have not only a well-developed upper
eyelid, but a nictitating membrane, moved by special muscles.

All Amphibia possess a fenestra ovalis with a cartilagi-
nous, or osseous, columelliform stapes, the expanded proximal
end of which is fixed tothe membrane of the fenestra. In
many Batrachia, if not in all, there is a fenestra rotunda,
though the presence of a distinct cochlea has not been ascer-
tained. The Urodela, the Gymnophiona, and the Pelobatidea,
among the Batrachia, have no tympanic cavity, nor mem-
brane. In the other Batrachia 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 tympanic 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 L’lasmo-
branchii, 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 kidney, and
traverse it, leaving its outer side to enter a genito-urinary
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 VERTEBRATED ANIMALS.

into the genito-urinary duct. In the Batrachia there is like-
wise a genito-urinary duct, and the vasa efferentia run to the
inner edge of the kidney and enter it. Jn Bombinator igneus
and Discoglossus pictus, the genito-urinary duct receives the
urinary products and the spermatozoa, in the same way as in
the Urodela. 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 Wolffian and the Millerian ducts of the
higher Vertebrata.

In most Amphibia the ova are impregnated and hatched
outside the body, but internal impregnation and incubation
occur in some of the Urodela. 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 Urodela, 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 Batrachia, 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 cesophagus. The nasal sacs are at first
mere czecal involutions of the integument, but nasal passages
communicating with the mouth are soon formed, and bot&
aérial and aquatic respiration are completely established.

THE DEVELOPMENT OF AMPHIBIA. 165

In the Batrachia, as development proceeds, the external
branchize 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.

eH At

ewe
ep ie
i gy ni
raf th nt

Ny

i

¥ia. 60.—A. B., Tadpoles with external branchiz: 2, nasal sacs; a, eye; 0, eur; & 0, bran-
chiz ; m, mouth; 2, horny jaws; 8, suckers; d@, opercular fold.

C., a more advanced Frog’s larva: 7, the rudiment of the hind-limb; % s, the single branchial
aperture. The figure has not been reversed, so that this aperture appears to lie 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 Batrachia 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 branchiz is
reéstablished ; and they become the permanent arches of the

166 THE ANATOMY OF VERTEBRATED ANIMALS.

aorta. The anterior branchiz are replaced by the carotid
glands, and their afferent vessel is the carotid passage of the
adult. The afferent and efferent trunks of the third pair of
branchiz are converted into the stem of the cutaneous artery,
and the afferent trunk of the fourth pair of branchiz 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
soiled up into a close spire, like a watch-spring, 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 Urodela the tail persists, and develops complete
vertebrze ; but, in the Batrachia, 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.

THE CLASSIFICATION AND THE OSTEOLOGY OF THE REPTILIA,

THE province Sauropsida is divisible into the two classes,
Reptilia and Aves.

All Reptilia, so far as their 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. The centra of the vertebrae may be amphiccelous, 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 vertebrz
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 Pterosauria). The sternum may be converted
into cartilage-bone, but (with the possible exception of the
Pierosauria) 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 vertebre 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 bigemina 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 vertebre,
at least, have subcylindrical articular faces. If, as in some
birds, the faces of the centra of the other vertebra are sphe-
roidal, they are opisthoccelous, which is the rarest arrange-
ment among reptiles.

3. The proper sacral vertebree 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 interclavicle 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 thefront 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 REPTILIA. 169

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 Dinosauria 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. The 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 Chameleons, and the extinct Pterodactyles very prob-
ably possessed such sacs.

11. The corpora bigemina 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 vertebra (which, like all the other vertebra, are devoid of
transverse processes) are not movable upon one another, nor are the ribs
movable upon the vertebra (Pleurospondylia). 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 a plastron,

I.—Chelonia.

B. The dorsal vertebre (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 (Zipe-
tospondylia),

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.

Il.— Plesiosauria,

b. 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 THE ANATOMY OF VERTEBRATED ANIMALS.

a, A pectoral arch and urinary bladder.
: Iit.—Lacertilia.
6. No pectoral arch, and no urinary bladder.
IV.— Ophidia.

b. The dorsal vertebrae have double tubercles in the place of transverge

processes (erospondylia). The limbs are paddle-like.
V.—Ichthyosauria.

e. The anterior dorsal vertebre have elongated and divided transverse
processes, the tubercular being longer than the capitular division
(Suchospondylia).

a. With only two vertebre in the sacrum.
VI.— Crocodilia.
6. With more than two vertebre in the sacrum.
a. The manus without a prolonged ulnar digit
1. The hind-limb saurian.
VII.—Dicynedontia.
2. The hind-limb ornithic.
VIUI.— Ornithoscelida.
6. The manus having an extremely prolonged ulnar digit.

IX.—Pierosauria.

I shall describe the exoskeletal, endoskeletal, and dental
systems of the chief groups of the /eptilia, 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 Curton1A.—The Tortoises and Turtles are those
reptiles which most nearly approach the Amphibia, 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 (Zrionyx), 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.
The dorsal surface of the body presents three series of central
plates, of which five are in the middle and four upon each side
(4, 5,4). The margins of the dorsal shield are guarded by
twenty-four or twenty-five plates; one on the middle line in
front, called nuchal ; one or two behind, pygal ; 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 de«
veloped on other parts of the body, and on the limbs.

The dermal ossifications may best be described in connec-
tion with the endoskeleton.

The presacral vertebree 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 vertebre.
In all the cervical vertebrze 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 twy superolat-
eral. The second is a true axis vertebra, the central part of
the centrum of the atlas ossifying apart, as an odontoid bone,
ond attaching itself to the front face of the centrum of the sec-
md vertebra.

The other cervical vertebree are remarkable for the singu-
lar variety in the disposition of their articular cups and balls.

Fig. 61.—The Alligator Terrapene (Chelydra Serpentwna).

Thus the third is opisthoccelous; the fourth, biconvex;
the fifth, proccelous; the sixth, also proccelous, 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 proccelous, and differs from the rest by the
_ expansion of its neural spine, and by the arching backward
of its postzygapophyses over the convex prezygapophyses of

172 THE ANATOMY OF VERTEBRATED ANIMALS.

the first dorsal vertebra, wpon which the former play back.
ward and forward.

All the cervical vertebrze are very freely movable upon
one another, and confer great flexibility on the neck. In
striking contrast with this arrangement, the ten following
vertebrze have flattened faces, firmly united by cartilage. If
any one of these vertebrae, 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, V).

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, IZ).

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

Fic. 62.—Transverse section of the skeleton of Chelone midas in the dorsal region: C1,
centrum; V, expanded neural plate; C, costal plate; , rib; J/, 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, Vw), 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

vertebra 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. Therib 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-
tebrze 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-

Fie. 68.—Dorsal view of the carapace of Chelone midas: Nw, nuchal plate: 37, marginal
plates; £, ribs; 1-8, neural plates; C.1-C.8, costal plates; Py, pygal plates.

sal vertebrze, 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 vertebree 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
serrated suture, lies a larve nuchal plate (Fig. 63, Wu), which

174 THE ANATOMY OF VERTEBRATED ANIMALS.

forms the anterior median boundary of the 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 another. The anterior two 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 vertebrae.

The sides of the carapace are completed, between the
nuchal and pygal plates, by eleven marginal plates (Fig. 63,
M) 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 vertebree
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 Chelonia. The plastron is
wholly composed of membrane-bones, which 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
fail may be named—the median, entoplastron ; the first

ateral, epiplasiron ; the second, hyoplastron ; the third, hypo»
plastron ; and the fourth, xiphiplastron.* The entoplastron
* Believing the plastron to answer to the sternum of other Vertebrata,

anatomists have termed these elements of the plastron entosternum, epister-
num, hyosternum, hyposternum, and xiphisternum.

ee é
d
..

THE PLASTRON OF THE CHELONIA. 175

and the two epiplastra correspond with the median and lateral
thoracic plates of the Labyrinthodont Amphibia, and very
probably answer to the interclavicle and clavicles of other
Vertebrata.

Fic. 64.—The plastron of the Green Turtle (Chelone midas): Il, interclavicle ; cl, clavi-
cles; Hy.p., hyoplastron; Hp.p., hypoplastron; Xp., xiphiplastron,

The sacrum consists of two vertebra. The expanded
sacral ribs are not anchylosed with the centra and arches of
their vertebra.

The tail is flexible, and consists of proccelous vertebre.

a
ees

Ay CAAA TIN

the NV Vea i it)

ies Wisin

eee

Pa a. ] ie
ON iy ry

o* i

Fic. 65.—External view of a section of the auditory region of the skull in a Turtle (Chelona
midas): f. 0., fenestra ovalis ; 7. 7., fenestra rotunda; esc, asc, psc, external, anterior,
and posterior semicire Ss. s

176 THE ANATOMY OF VERTEBRATED ANIMALS.

The anterior caudal vertebrze have no transverse processes,
but possess ribs which may not become anchylosed with the
centra. Thus the tail and the neck are the only regions of
the spinal column of a Chelonian which are flexible.

In the skulls of the Chelonia all the bones, except the
mandible and the hyoidean arch, are immovably united to- .
gether.

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, which plays the part of an alisphenoid. Neither
the presphenoid nor the orbitosphenoids are represented by

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fie. 66.—Longitudinal sections of the skull of the Turtle. The upper figure represents the
entire skull with the outline of the brain 77 sitw; the lower gives a larger view of the
inner face of the bones of the p»sterior moiety of the skull.

ay

THE CHELONIAN KULL. 177

bone, but there are large frontals. In the periotic capsule the
large prodtic and the opisthotic (Cuvier’s occipitale 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 premaxillze
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-

frontal} 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.

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
are firmly fixed to the base of the
skull, as in Plestosauria and Croco-
dilia. They unite only with the up-
per part of the quadrate bone, as in
the latter reptiles.

The palatines are firmly united Fic. 67—The left half of the un
epee Vahind/and with |: eee eekot ae
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. (lig. 67, Vo, V*.)

L78 THE ANATOMY OF VERTEBRATED ANIMALS.

The dentary pieces of the two rami of the mandible are
represented by one bone, as in Birds,

The hyoidean apparatus consists of a broad plate of car-
tilase 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 Vertebrata, 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 Vertebrata. 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 Lacertilia. There
is no clavicle, unless the epiplastra and entoplastron represent
that bone.

The carpus of the Chelonia contains nine primary ossicles,
as in the Urodela—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 obturatoria 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 Chelys, 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 astragaius, formed by the union of the ¢ibiale and interme-
dium, and of a fibulare or caleaneum. In Chelydra there is a

THE DIVISIONS OF THE CHELONIA. 179

centrale. InChelone, Hmys, Testudo, and Trionyx the centrale
is united with the aséragalus ; and in Himys, the calcaneum
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 Zestudinea there are only two phalanges in each
digit of the pes.

The Chelonia are divisible into the Testudinea, the Lmy-
dea, the Trionychoidea, and the Huereta.

1. The Zestudinea 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 Pyzis)
the anterior part of the plastron is movable, and can be shut
up like a lid. In Cinyzis, the hinder part of the carapace is
similarly mobile.

2. The Himydea have, usually, horny cutting jaws, un-
covered by lips; the tympanum exposed, and the limbs more
slender than in the Zestudinea, 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 which, the Zerrapenes,
the pelvis is free, the neck bends in a vertical plane, and the
head is almost completely hidden by the carapace when re-
tracted (Himys, Cistudo, Chelydra). In Cistudo, Cinostenum,
and Staurotypus, the hinder part of the plastron is mobile.
In the other division, the Chelodines, the pelvis is fixed to the
carapace and plastron, the neck bends sideways, and the
head cannot be completely retracted under the carapace
( Chelys, Chelodina.)

3. In the Zrionychoidea (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
ligits have nails. The integument develops no horny plates,

180 THE 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 Gymnopus, Cryptopus, and Cycloderma, con-
stitute this division; they all inhabit the fresh waters of hot
latitudes.

The Huereta, 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 (Sphargis), or covered with
thick epidermic plates ( Chelone.)

The two genera composing this group 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 Huereta and the Trionychoidea, but present no
approximation to any other order of /eptilia.

II. The Prustosavria.—In some of the FPlesiosauria, 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-
ably, 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-by in the structure of
the Crocodilia, to take the last of the vertebre in which the

THE PLESIOSAURIA. 182

costul articular surface is cut by the neurocentral suture, as
the last of the cervical series.

The two anterior cervical vertebrae, as thus defined, con-
stitute the atlas and axis, and are frequently anchylosed to-
gether, The centre of the other cervical vertebrze have slightly
concave anterior and posterior surfaces ; well-developed neural
arches; anterior and posterior oblique processes, or Zygas
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
iuto 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 Crocodilia. In the posterior part
of the neck and the anterior part of the 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-
bre. (Fig. 68, C.)

In the anterior dorsal vertebrz, these transverse processes
rapidly acquire their full length; and they are continued un-
der this form, descending somewhat lower upon the arches of
the vertebree 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 vertebra are two, and resemble
the others, except that the sacral ribs are large and broad for
the attachment of the ilium. The caudal vertebra, 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 vertebree. .

As has been mentioned, there appear to be no sternal ribs,

182 THE ANATOMY OF VERTEBRATED ANIMALS.

YW * Co.

Fra. 68.—Diagram showing the structure of the most important parts of the skeleton of
Plesiosuurus.—A, the skull: Wa, nasal aperture.—B, the left fore-limb: H, humerus;
U, ulna; #, radius; 7. 7. u., radiale, intermedium, and ulnare, in the proximal row of
carpal bones; 1, 2, 3, distal carpal bones; J/c, metacarpus; Ph, phalanges.—C, a dorsal
vertebra with ribs (7.), and ventral ossifications ( V.o).—D, the left hind-limb: /, femur;
T, tibia; F, fibula; 7. 2.7, tibiale, intermedium, and fibulare, in the proximal row of tar-
gal bones; 1, 2, 3, distal tarsal bones; J/7, metatarsus; P/, phalanges.—E, the pectoral
arch: Sc, scapula; Co, coracoid; a, clavicles and interclavicle (?).—F, the pelvic arch:
Pb, pubis; L/, ilium; Zs, 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 Plesiosauria, as already 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,
like the supra-temporal fossee, 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 jugal 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 Plesiosaurus
differs from that of most Reptilia 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 fossz 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 true posterior nares, and that the posterior aper-
tures are simply spaces left between the pterygoid bones and
the basis cranizi.

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 anchy losed.

The pectoral arch (Fig. 68, E) is’ one of the most remark-
able parts of the organization of the Plestosauria. It consists,
in the first place, of two very large coracoids, the long axes
of which are parallel with one another, while their inner r edges
meet, without overlapping, throughout the greater part “of
their extent. In this respect they differ from any of the
Lacertilia, which 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 Plesiosauria,
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 Batrachia.

The scapulze are unlike the corresponding organs in any
other reptile. The glenoidal end, stout and strong, is con
tinued 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, Jguana.

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 body, 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 Plesiosaurus, though they appear to
have been well developed in othosaurus.

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 the 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
Pilesiosauria, which are long extinct animals, entirely confined
to the Mesozoic Rocks, from the Trias to the Chalk, inclusive.
They may be divided into two groups, according as they are
Triassic, or Post-Triassic, in age.

The Post-Triassic group contains the genera Plesiosaurus
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 whether 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.

L86 THE ANATOMY OF VERTEBRATED ANIMALS.

of the vertebre. In the species which have been named
Pliosaurus, the vertebree are wide in proportion to their
length, and deeply excavated in front and behind. Piosaurus
attained gigantic dimensions, paddles of some individuals
reaching a length of not less than six feet.

The Triassic genera, Wothosaurus, Simosaurus, Pisto-
saurus (for a knowledge of the organization of which we are
chiefly indebted to the labors of Hermann von Meyer), appear
to have differed from Plesiosaurus principally in the following
respects:

The connection of the neural arches with the centra of the
vertebre seems to have been looser. The supra-temporal
fossze 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 Plesiosaurus, but apparently lacks the poste-
rior fossze; while there is no doubt whatsoever that the true
posterior nares are situated far forward, in the position as-
signed to them in Plesiosaurus.

The pectoral arch of Wothosaurus, 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 rhomboidal part of the sternum seems to
have been wholly absent, and the scapulz have a horizontal
prolongation, not quite so long as in Plesiosaurus, 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.

Ill. The Lacertiz1a.—Some few Lacertilia, like the Cha-
meleons and the Amphisbene, 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.¢., Scincus, Cyclodus) 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 vertebree; and, except in the Amphisheene and some few
other Lizards, the tail is long. Those Lizards which possess
hind-linbs have a sacrum, into which not more than three
vertebre, and rarely more than two, enter. The presacral
vertebre are distinguishable, when sternal ribs are present, into
cervical and dorsal. All those vertebrze 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 vertebree 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-
tebra. Such a separate ossification, or sub-vertebral wedge-
bone, is commonly developed beneath and between the odon-
toid bone and the body of the second vertebra.

The centra of the vertebre are either proccelous, or amphi-
ecelous; the former being by far the more common condition
in existing Zacertilia, all of which, except the Geckos and
Spyhenodon, have proccelous vertebre. The cups and balls
are usually ellipsoidal, the long axis of the ellipsoid being
transverse. In the Geckos, the centra of the vertebre are
conically excavated at each end; and, except in the centre of
each vertebra, where it is ossified, the notochord persists
throughout the spinal column.

The sacral vertebree 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 the tail of the Lacertilia there are
usually well-developed subvertebral chevron bones, which are
commonly attached to the bodies of the several vertebra, and
not in the intervals between adjacent vertebre. In many
Lacertilia (Lacerte, Iguance, Geckos) the caudal vertebree
have a very singular structure, the middle of each being tray-
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 VERTEBRATED ANIMALS.

appendage is pretty certain to part at one of these weak
points.

The arches of the vertebre of the Lacertilia are articulated
together by the ordinary oblique processes, or zygapophyses.
In the Jguane they are additionally connected by a process
of the front part of each arch (zygosphene), which fits into a
fossa on the posterior face of the preceding arch (zygantrum).
These Lacertilian vertebree thus nearly approach the vertebrae
of the Ophidia.

The transverse processes of the vertebre 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 processus uncinatt. 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, Chamee-
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
Amphisbene), and in the absence of alisphenoids, or of any
complete ossification of the presphenoidal or orbito-sphenoidal
regions. The premaxillz and maxille are firmly united with
one another and with the skull, and there are two vomers. An
unossified space, the parietal foramen, usually remains in the

THE LACERTILIA. 189

roof of the skull in the course of the sagittal suture, or between
the parietals and the frontals.

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Fie. 69.—The skull of Cyclodus, entire and longitudinally bisected.

In the principal group of the Zacertilia, a column-like
membrane-bone, called the colwmella (but which is not to be,
by 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 “Aitonocrania,” or “ column skulls.” This colu-
mella (Fig. 69, Co) appears to correspond with a small inde-
pendent ossification, which is connected with the descending
SS of the parietal and with the pterygoid, in some Che
onid.

In the great majority of the Zacertilia (as in the Chelonia),
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 prodtic
bones enter. Hach quadrate bone is articulated with the outer

190 THE ANATOMY OF VERTEBRATED ANIMALS.

end of one of these processes (in which a small separate péero-
tic ossification sometimes appears), and is usually movable.
The parietal bones do not unite suturally with the occipital
seoment of the skull, or with the prodtic 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, slightly movable upon the occipito-sphenoidal part.

Hach 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
Sphenodon, among recent Lizards, 1 is the jugal connected with
the distal end of the quadrate by bone. Asa general rule, the
quadrato-jugal is represented only by a lizament,

In consequence of the structure which has been described,
the posterior region of the ordinary Lacertilian skull presents
a number of distinct fossze 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; a post-temporal, between
the parietal, the occipital, and the parotic apophysis on the
posterior face ; a lateral-tempora!l, between the squamosal and
post-frontal above, the jugal and quadrate in front and behind,
and the quadrato-jugal ligament below.

The palatine and pterygoid bones are firmly connected both
with the facial bones, and with the floor of the skull. Thus
the basisphenoid sives off two basipterygoid 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, Zr) usually passes, to unite the palatine and
pterygoid with the maxilla.

The anterior ends of the palatines unite with the maxille
and the vomers; but, in existing Zacertilia, they do not meet
one another, or ‘come into contact with the basisphenoid or
presphenoid i in the middle line. The palatine apertures of the
nostrils are placed between the palatine bones, on the outer
side, and the vomer, on the inner. In only a few Lacertilia
do the palatine bones send down processes which bend tow-

THE LACERTILIA. 19]

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 articulare.

The hyoidean apparatus consists of an
elongated median rod, the anterior part
of which supports the base of the tongue 3
and, usually, of two long cornua on each
side of this. ‘The cephalic ends of the an-
terior cornua may be perfectly free, and
lie upon the sides of the neck, as in Psam-
mosaurus ; or they may be traceable to,
and be connected with, the stapes and
the parotic processes, as in Sphenodon,

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
digits from two to five. Even when the
limbs are altogether absent, the pectoral
arch remains, though the pelvic arch Hi. 70—Under-view of the

= skull of Cyclodus: N:,
seems to vanish. When the pectoral arch _ posterior nasal aperture.
is complete, it consists of a suprascapula,
scapula, coracoid (with precoracoid and epicoracoid elements),
and two clavicles, united by an interclavicle, which lies ina
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 Zialis, 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 between 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-

192 THE ANATOMY OF VERTEBRATED ANIMALS.

coid is invested, and in part replaced, by a sheath of membrane:
bone, which expands above and below, and represents both
scapula and coracoid, though it presents no trace either of
division, or of a glenoidal cavity. Beyond the 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 composed 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 (Anguis)
and the Sheltopusik (/sewdopus), is in much the same con-
dition as in Lidlis.

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 off a strong
curved process. In many Lacertilia a partially-ossified or car-
tilaginous rod (0s cloacw) is continued back from the sym-
physis of the ischia, and supports the front wall of the cloaca.

In most Lacertilia the manus possesses five digits; and,
when 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, the 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. ‘I'wo large bones, very clcsely 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 appear 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 element, and repre:
sent not only the fifth metatarsal, but the corresponding distal ¢arsale.

Sr eS eee a
a
“3

THE LACERTILIA. 193

The Zacertilia all possess teeth, which may be confined
to the premaxille, maxille, 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 (Monitor); or blade-like, with serrated edges
(Lguana); or with broad, crushing, and spheroidal crowns
(Gyolodies). 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 pleuro-
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 Lacertilia are divisible into numerous groups, the leading distinctive
ekaracters of which are exhibited ir the following table:
I.—The pterygoid and quadrate bones united.
A. A columella and an interorbital septum in the skull.
Kionocrania (Stannius).
a. Amphiccelous vertebrae (K. Amphicelia),
a. Dentition acrodont or pleurodont.
1. Ascalabota.
2. Rhynchocephata,
3. Homeosauria.*
6. Dentition thecodont (?).
4. Prolorosauria.*
b. Proccelous vertebrae (K. procelia).
a. Not more than nine cervical vertebra.
a. The nasal bone, single.
5. Platynota,
b. The nasal bones, two.
1, The integument of the head not
covered with epidermic plates.
6. Hunota.
2. The integument of the head covered
with epidermic plates,
". Lacertina.
8. Chalcidea.
9. Scincoidea.
b. More than nine cervical vertebree.
10. Dolichosauria,*
11. Mosasauria,
B No columella; no interorbital septum.
12. Amphisbenoida.
IJ.—The pterygoid and quadrate bones disunited.
13. Chameleonida.

* The columella has not been observed in these groups.

9

194 THE ANATOMY OF VERTEBRATED ANIMALS.

1. The Ascalabota.—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 Remora,
or Sucking-fish.

The most important and distinctive characters of these
Lizards are:

Their vertebrze are amphiccelous.

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 Rhynchocephala.—vThis division contains only the
very remarkable genus Sphenodon (otherwise Hatteria, or
Rhynchocephalus). 'The vertebrz 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 wails of the tympanum. The dentary pieces of the
mandible are not suturally united. The premaxillz are not
anchylosed together, and, as in some other Lizards (e. g., Uro-
mastix), have a beak-like form, the large premaxillary teeth
becoming completely fused with the bony substance of the
premaxillz. There is a longitudinal series of teeth upon the
palatine 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 PRC TOROSAURIA. 195

another down to the bone in such a way, that the mandibular
teeth are ground to an edge, while the maxillary and palatine
teeth are worn upon their inner and outer faces respectively.

The extinct Lizards of the Triassic age, RAynchosaurus and
Hyperodapedon, appear to have been very closely allied tc
Sphenodon.

3. The Homcosauria.—The remains of Lizards of small
size, and agreeing in the most important points of their osteol-
ogy with the ordinary Lacertilia, but having amphiccelous ver-
tebree, have been found in the older Mesozoic rocks, from the
Solenhofen slates to the Trias inclusively. They cannot be
identified with either the Lhynchocephala, or the Ascalabota,
and may be provisionally grouped as Homcosauria. 'The
genera Homcosaurus, Saphoeosaurus, and Telerpeton, belong
to this group.

4, The Protorosauria.—These are the oldest known Sauw-
yopsida, their remains occurring in the Kupferschiefer of
Thuringia, which 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
have 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 well 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
vertebree. In all these vertebrz 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 vertebree 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. Inthe 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 near

L196 THE ANATOMY OF VERTEBRATED ANIMALS.

the middle of the tail, have the ordinary structure; but beyond
this point they bifurcate, so that each vertebra seems to have two
spinous processes, a peculiarity unknown in other Lacertilia.

The large chevron-bones are articulated between the bod-
tes of the caudal vertebra, as in the Crocodilia, but also as in
some Lacertilia, 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, 3;
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 which 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
vertebra, 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 Heloderma, 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 fossz. 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 Dolichosauria.—A very singular Lacertilian found
in the Chalk, and resembling an eel in form and size, has been

Se Oe ee a

THE MOSASAURIA. 197

described by Prof. Owen under the name of Dolichosaurus.
It possesses an exceedingly elongated body, but is provided
with limbs and with a distinct sacrum, consisting of two ver-
tebree. Its most remarkable peculiarity, however, lies in the
number of its cervical vertebrze, which were not fewer than
seventeen.

11. Zhe Mosasauria.—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.

Highty-seven vertebrze 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 vertebrze 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 vertebrae are concave in front and
convex behind; but the concavities and convexities are less
marked in the posterior, than in the anterior, vertebra. The
atlas and axis are not well preserved in this series of vertebre,
but the nine following all have inferior spinous processes,
which become shorter in the posterior vertebra, 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
vertebre. 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, vertebrz. There are no inferior processes. All the
vertebrze 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 long, 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
vertebree 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
vertebre 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 VERTEBRATED ANIMALS.

one another. And, in the hindermost caudals, the spinous
processes and the chevron-bones disappear.

There were strong ribs, but nothing is known 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. But
sharp recurved teeth are anchylosed by their bases, not only
to the premaxillary, maxillary, 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. Zhe Amphisbenoida.—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 arez arranged in transverse rows. The
tail is exceedingly short, so that the vent is close to the end
of the body.

The numerous proccelous vertebrae have less elliptical
articular faces than those of the typical Lacertilia. There is
no sacrum, and all the precaudal vertebra, 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 vertebree. The vertebree have no zygantrum nor zygo-
sphene. Amphisbena 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 Amphisbeena the premaxille bear two rows of teeth,
one behind the other, and one tooth lies upon the symphysis
of the premaxille.

13. The Chameleonida.—The Chameleons are distin-
guished from the étionocrania not only by the negative

a se ee

ace

THE CHAMELEONIDA. 199

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 pollex, 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 vertebrze of the Chameleons are similar in their char-
acters to those of the proccelous Avionocrania, The sacrum
is composed of only two vertebree. 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 Chame-
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 Chamzleon its remarkable
casque-like form. The frontal bone is comparatively small and
single, and the nasals are very narrow, and do not bound any
vart of the anterior nasal apertures. 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 Chameleons 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 Lacertilia, movable upon
the sides of the skull, but is firmly anchylosed with the bones

200 THE ANATOMY OF VERTEBRATED ANIMALS.

which lie adjacent to its upper end. The pterygoid bones
are produced downward; and, by 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 Zacertilia. 'There are no clavicles, and the inter-
clavicle is wanting, 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 Chamee-
leons differ very much from the ordinary Lacertilia. There is
no os cloace.

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 Oruip1a.—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. Aglyphodontia.
6. Some of the posterior maxillary teeth grooved.
2. Opisthoglyphia.
e. Grooved anterior maxillary teeth succeeded by solid teeth.
8. Proteroglyphia.
d, Maxillary teeth few, canaliculated, and fanglike.
4. Solenoglyphia.

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. Typhlopide.

THE OPHIDIA. 201

All the Snakes possess a scaly epidermic investment, which
is 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 Acrochordus, they become
more tubercle-like, and do not overlap. In the Rattlesnakes
( Crotalus) the body is terminated by several loosely-conjoined
rings of. horny matter, which consist of the modified epidermis
of the end of the tail. i

The derm does not become ossified in the Ophidia.

The number of the vertebrze in the Snakes is always con-
siderable, 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-
Zions, as there is no sacrum, nor any distinction between cer-
vical, dorsal, and lumbar vertebrae. 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 Lacertilia, 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

Fia. 71.—Anterior and posterior views of the dorsal vertebra of a Python: 2. s., zygosphene;
2. @., Zygantrum; p.%., prezzgapophyses; pt. 2., postgygapophyses; 7. 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 VERTEBRATED 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; 1t 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-
bre. 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 vertebra 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 premaxille are usually
represented by a single small bone, which very rarely bears
teeth. It is connected with the maxille 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 maxille 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

se

THE OPHIDIA. 303

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 Vertebrata. '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

iM Ny
“ath

uty) WAM aati v

ores oh 1 pi it nN a A

elit tal Midi, N\ 3 I) an
‘ Ay

i
Jie

fie. 72.—The skull of a Python, viewed from the left side, and in longitudinal section: Cin,
stapes; 77, turbinal bone.

Ophidia 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 trabecule cranii of the foetus,
which do not become united in Snakes, as they do in all the
other abranchiate Vertebrata. 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 trabecule. 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 Chelonia, and the frontals unite in the middle line of the
floor of the skull in some Mammals); and as there are only

204 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 represent 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
side are formed from single centres of ossification, which ap-
pear in patches 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 reéxamined.

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 (77, 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 Vertebrata. 'The squamosals
are usually well developed. There is no jugal, or quadrato-
jugal,
SThough the general conformation of the skull in the Ophid-
ia is that which 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,

E aia

THE OPHIDIA. 205

But, in the remarkable group of the Z'yphlopidc, 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 Batra-
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 maxillz are short
plates 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 Tortria
(which belong to the division Aglyphodontia); at the other
the poisonous Snakes, and especially Crotalus (Solenoglyphia).

Thus, Python (Figs. 72 and 73) has well-marked premaxilla,
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 jf:
a long series of recurved teeth, which ”%
are not very unequal in size. And Py- |
thon (like Zortrix, but unlike all other
Ophidia) possesses teeth in the premax-
illee.

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. gs
The rami of the mandible are loosely
connected by an elastic symphysial liga-
ment. ‘Thus, not only can these rami
ke widely separated from one another, XX
but the squamosal and quadrate bones aS
constitute a kind of jointed lever, the
straightening of which permits of the PSP em tae
separation of the mandibles from the cialbones of Python.

206 THE ANATOMY OF VERTEBRATED ANIMALS,

base of the skull. And all these arrangements, taken together,
allow of that 1mmense distention of the throat which is requi-
site for the passage of the large and undivided prey of the
serpent.

In Tortriz, this mechanism does not exist, the short quad-
rate bone being directly articulated with the skull, while the
squamosal, like the post-frontal,isrudimentary. The maxillary
bones are also almost fixed to the skull.

In the Rattlesnakes (Crotalus, Fig. 74), the premaxille
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
par connected posteriorly with the pterygoid.

Pa. 74.—A, the skull of Crotalus, viewed from the left side; B, a transverse section taken
at the point. B, in Fig. A, showing 7; the persistent cartilaginous trabecule. The max-
illa is supposed to be transparent, and the anterior half of the palatine bone is seen
through it,

if
*
:

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 pterygoid.

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-
fangs are attached, to look backward. Hence these fangs 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 pterygo-palatine joint;
secondly, the partial rotation of the maxillary upon its lachry-
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 poison-
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 Typhlopide, the Pythons, Boas, and Zortrices, have
rudiments of a pelvis, and the latter Snakes even possess very
short representatives of hind-limbs terminated by claws,

The teeth of the Ophidia are short and conical, and be-
come anchylosed to the bones by which they are supported.

208 * THE ANATOMY OF VERTEBRATED 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
Uropeltis and some other genera, there are no palatine teeth;
and in the egg-eating African snake, Ltachiodon, 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 vertebre are long, and tipped, at their apices, with a
dense enamel-like substance. These project through the
dorsal wall of the cesophagus 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 Icuruyosaurta.—In its general form Jchthyo-
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 Jchthyosaurus may
have been provided with a sort of fin-like expansion of the
integument. This fish-like body was propelled, like that of
the Plesiosaurus, by four paddles; but the anterior paddles
were placed close behind the head, and were, generally, very
much larger than the posterior ones.

NY CQrree

Fig. 75.—A restoration of Ichithyosaurus. The existence of the caudal fin is doubtful

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

Y}

S})) 5

)

)
f'

Fic. 76.—Different parts of the skeleton of Ichthyosaurus intermedius, drawn to the sams
seale. A, the skull; B, the fore-limb: H, humerus; FR, radius; U, ulna; 7”. ¢. w., radi-
ale, intermedium, ulnare; Cp, carpalia; 1, 2, 3, 4, 5, digits; 2.2. m.w. radial and ulnar
marginal ossicles—C,a dorsal vertebra, with the ribs (2) and ventral ossifications
(V.0).—D, the hind-limb: #, femur; 7, tibia; F’}, fibula; 7%, 2,7 tibiale, intermedium,
fibulare; 7s, tarsalia; 2/7, metatarsalia; Ph, phalanges; m, tb, tibial marginal ossicles
—E, the pectoral arch, seen from the ventral side ; F, the same aspect of the pelvic arch

210 THE ANATOMY OF VERTEBRATED ANIMALS.

tinguished by the chevron-bones which are attached beneath
its vertebrae. The vertebrze of Zchthyosauria in general have
certain characters by which they 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 which they resemble the
vertebrze 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 vertebra, 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 may call “neck” the most
anterior part of the vertebral column, the front part 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 vertebra. 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 vertebre 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 Lchthyosaurus (Fig. 76, A) is remarkable for
the great elongation and tapering form of the snout, the huge
orbits, the great supra-temporal fossa, and the closing over of
the infra-temporal fosse by plates of bone. Again, the two
rami of the mandible are united in a symphysis, which, for
length, is comparable to that observed in the modern Gavials
and in the ancient Teleosauria. The basi-occipital bone fur-

res SNS Sal
i AL
=

THE ICHTHYOSAURIA, 211

nishes the round articular condyle to the first vertebra, and
becomes very stout and thick in front. It appears to have

een 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
long 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 prodtic 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 prodtic. If
this bone were not so large, it might well be regarded asa
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 premaxilla make up by far the greater part of the
snout, The maxille 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, Pf. O). A broad and flat quadrato-jugal
( Q.j.) 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, S¢.), 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 VERTEBRATED 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 with 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,
which 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. Hach ramus is com-
posed of the normal six pieces, the splenial being remarkably
long, and entering extensively 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 (Se), 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 ; so that, in this genus also, the rhom-
boidal part of the sternum appears to have been absent or
very small,

But there is a very distinct T-shaped interclavicle (Z CZ),
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 clay-
icles (Cl.), 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 clay-
icles and interclavicle presents interesting conditions inter-
mediate between those observed in WVothosaurus, on the one
hand, and those common in the Lacertilia, on the other.

The scapula and coracoid give rise by their junction to a
glenoidal cavity, into which the thick head of the very short
prismatic humerus (Fig. 76, B, #7) 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
the radius and the ulna (#,U). 'To these succeed two rows
of smaller polygonal ossicles in the place of a carpus: three,
representing the radiale, intermedium, and ulnare (r. 7. u.),
lie in the proximal row, and three or four carpalia ( Cp.) in
the distal row. With the distal carpal bones are connected,
by means of the metacarpal ossicles (JMc.), 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 bones * to the
radial and to the ulnar edges of the manus (m.u., m.r.). There
is thus formed a paddle, which is unlike either that of a Ce-
tacean, or that of a Plesiosaurus, 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.
(ig. 76, Cy Vo0O.)

The pelvis (Fig. 76, F) is not connected by bone with the
vertebral column. It consists of an ilium (Z/:), an ischium
(Js.), and a pubis (P8.), 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 appertaining to Ichthyosau-
rus 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.

* I leave open the question whether these series of marginal ossicles are
remains of the digits of a polydactyle 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 including, 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 (LI. inter-
medius, communis, etc.); and such as have longer snouts, long
paddles, and three carpalia (I. longirostris, tenuirostris, pla
tyodon).

VI. The Crocopir1a.—Crocodiles, the highest living Rep-
tilia, 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 which 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 Gavials) 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 Stagonolepis 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 rings 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 Hastingsie,
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. 215

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-
isting 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-
tebrz is twenty-four; that of the sacral, two, in all the recent
forms, and probably in the extinct genera also. The number
of the caudal vertebrze varies, but is not less than thirty-five.
The number of the cervical, dorsal, and lumbar vertebre 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 vertebre, except the atlas
and axis, the two sacrals, and the first caudal, are proccelous.
The majority of the pre-cretaceous Crocodilia have the corre-
sponding vertebrze amphiccelous, the concavities of the centra
being very shallow. One genus, Streptospondylus, which is
perhaps Crocodilian, has the anterior vertebree opisthoccelous.
It is characteristic of the Crocodilia, that the centra of the
vertebree 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 vertebrz all possess ribs with distinct and long
capitula and tubercula—the Jatter 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 well as behind, the junction
of the capitulum with 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 vertebra
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 ribs

216 THE ANATOMY OF VERTEBRATED 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 vertebra, the
neurocentral suture passes. But in the tenth and in the eley-
enth vertebrz, the capitular process, which lies nearer the
neurocentral suture in the posterior than in the anterior cervi-
cal vertebre, rises upon the body of the vertebra to the level
of the neurocentral suture, by 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
eapitular, 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 vertebre, while
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 vertebre, lies
below the root of the transverse process, which, therefore, is
wholly 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 vertebrze 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 which the distinction between capitulum and
tuberculum is lost.

The lumbar vertebrze have long transverse processes which
arise from the neural arches, i.e., above the neurocentral su-
ture.

The centra of the two sacral vertebre 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, while 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 a part of the definition of a ‘‘ parapophysis,” that it is anto-
enous, there are no parapophyses in the vertebre of the Crocodilia ; and if it
e part of the definition of a ‘ pempophyeis ” that it arises from the centruin,

the dorsal vertebre of the Crocodilia have no parapophyses.

THE CROCODILIA. 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
proccelous; 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 Crocodilia, 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, Pu.) These are the
so-called “uncinate processes,” which also exist in Hatieria,
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 rectz
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 Labyrinthodonta. Hach
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 cf especial notice:

1. There is an interorbital septum, and the presphenoidal
and orbitosphenoidal regions remain cartilaginous, or very
incompletely ossified.

10

218 THE ANATOMY OF VERTEBRATED ANIMALS,

a Ue
< A all ne

aes SS m ae Tomy *N
Ry 5 Het ATER ORS

Win

iN \

ee NN

SONNY

Nik

=~ ‘is

ba: NY
ey

eget

Fie. 77, —Longitudinal and vertical section of the hinder Dart of the skull of a Crocodile:
Lu, Eustachian tube: P WV, posterior nares; P, pituitary fossa.

2. All the bones of the 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 quadrato-jugal bones;
supra-temporal, lateral-temporal, and post-temporal fossa are
formed, as in the ZLacertilia, 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-
malia ; and in all existing Crocodiles, but not in Zeleosaurus
or Belodon, the pteryg voids are also modified in the same way
fas 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 alisphenoids, but the orbitosphenoids
are absent or rudimentary.

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 Chelonia ; 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 pterygoid 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 proétic 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 sice
(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 Crocodilia, 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 VERTEBRATED ANIMALS.

the portio 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 Jlenticulare, 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 lenticulare.

The three radial digits are much stronger than the two
ulnar, and the numbers of the phalanges are 2, 3, 4, 4, 3,
counting 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.
The 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 pubis remains cartilaginous,
or imperfectly ossified, the bones, in imperfectly prepared
skeletons, appear as if they formed no symphysis.

The 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 caicaneal 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 larger, lie between the caleaneum and the third,
fourth, and rudimentary fifth, metatarsals. A thin plate of

THE CROCODILIA. 991

cartilage is interposed between the distal end of the astragalo-
navicular and the second metatarsal, and unites with the head
of the first metatarsal.

As in the manus, the three, pre-axial, clawed, digits are
stronger than the others. ‘The fifth is represented only by an
imperfect metatarsal. The numbers of the phalanges are
2, 3, 4, 4, counting from the tibial to the fibular side.

In the Crocodilia the teeth are confined to the premaxillz,
maxille, and dentary part of the mandible. They are simple
in structure, have large pulp-cavities, are lodged in distinct
alveoli, and are replaced by 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 Crocodilia 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 procelous presacral vertebra, 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. Alligatoride.
Alligator. Caiman, Jacare.

6, 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 premaxilio-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. Crocodilide.
Crocodilus. Mecistops.

222 THE ANATOMY OF VERTEBRATED 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 grooves in the margin of the upper jaw.
The premaxillo-maxillary suture acutely angulated backward. The
mandibular symphysis extends to at least the fourteenth tooth, and
the splenials enter into it. The cervical and tergal scutes form a
continuous series.

3. Gavialide.
Tthynchosuchus. Gavialis,

B. With the presacral vertebre amphiccelous (the anterior vertebre
sometimes cpisthoccelous (?) ); and the posterior nares bounded by
the palatines, the pterygoids not being united below. (All these
Crocodiles are extinct and pre-cretaceous. )

2. With the external nares terminal.

4. Veleosauride.
Leleosaurus. Goniopholis.
Streptospondylus. Stagonolepis, Calesaurus (?).

b. With the external nares on the upper part of the base of the snout
near the orbits.
5. Belodontide.,
Belodon.

There is a large number of extinct Lteptilia which resemble
the Crocodilia in the characters of their pre-sacral vertebra,
but differ from them, and resemble Lacertilia Chelonia, or
Birds, in other respects.

These are the Dicynodontia, the Ornithoscelida, and the
Pterosauria.

VII. The Dicynopontia. — Dicynodon and Oudenodon —
are lacertiform animals, sometimes of large size, with crocodil-
lan vertebree, four or five of which are anchylosed together to
form a strong sacrum. The skull is massive and lacertilian in
most of its characters; but the jaws are like those of the
Chelonia, and were 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 clay-
icle. The pelvis is very strong, with widely-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 the Triassic formation, in
India and South Africa, and the Ural Mountains.

THE DICYNODONTIA.

Se)
bo
[o)

Fic. 78—The pelvis and hind-limb of, A., Dromeus; B., an ornithoscelid reptile, such as
Iguanodon, or Hypsilophodon; and C.,a Crocodile. The bird’s limb is in its natural
position, as is that of the Ornithoscelid, 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. J/, ilium; Js, ischium; Pb, pubis; a, anterior process, D,
posterior process, of the ilium; 77, inner trochanter of the femur; 7, tibia; /, fibula;
As, astragalus; Ca, caleaneum. J., JZ, IZ, IV., the digits.

VUI. The Ornirmoscetipa.—The very remarkable extinct
reptiles which constitute this group, present a large series of

modifications intermediate in structure between existing Rep
filia and Aves.

294 THE ANATOMY OF VERTEBRATED 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 pree-acetabular pro-
cess, extends farther downward than the posterior pier, or
post-acetabular process.

But, in all the Ornithoscelida, 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 Ithea. The ischia never come to-
gether directly in a median ventral symphysis, though they
unite dorsally in hea. 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 Ornithoscelida (Fig. 78, B.), in which I have
been able to identify the bone (Zhecodontosaurus, Terato-
saurus, Megalosaurus, Iguanodon, Stenopelyx, Hadrosaurus,
LTypsilophodon), the ischium is greatly elongated. In Jguan-
odon it has the obturator process characteristic of the same
bone in Birds; and I imagine that the same process is seen in
Compsognathus. In Hypsilophodon there can be no mistake
sbout the matter, and the remarkable slenderness and prolon-
ration of the ischium give it a wonderfully ornithic character.

THE ORNITHOSCELIDA. 225

In Zguanodon the slenderness and prolongation are even car-
ried beyond what are to be seen in Birds. I am disposed to
think, however, that, as was certainly the case in Hypsilopho-
don, the ischia united in a median ventral symphysis in all the
Ornithoscelida.

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 Compsognathus 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 Compsognathus, would be very
similar in form and direction. Hypsilophodon, 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 Ornithoscelida. The remains of
Compsognathus and of Stenopelyx tend to skow 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
guter 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. %8) 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 strong ridge 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 ascending
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 tbialis anticus and extensor com-
munis, 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
thea, and in some breeds of fowls).

In the Ornithoscelida :

1. There 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.

A, 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. j

6. The astragalus appears to have remained distinct from
the tibia throughout life in Jyuwanodon, Megalosavrus, and

THE ORNITHOSCELIDA. 227

many other genera; but it seems to have become anchylosed
in Compsognathus, Ornithotarsus, and Huskelosaurus.

The reptiles belonging to this group are for the most part
of very large size, and some of them, as the Jgyuanodon, are
among the largest of known terrestrial animals. ‘They oc-
cur throughout the whole range of the Mesozoic formations,
being represented by Zhecodontosaurus, Palwosaurus, Tera-
tosaurus, Platcwosaurus, and other genera in the Trias; by
Scelidosaurus in the Lias; by MWegalosaurus, Poikilopleuron,
Euskelosaurus, Hyleosaurus, Polacanthus, Acanthopholis,
Iguanodon, Hadrosaurus, Trachodon, and Laelaps in the
middle and upper Mesozoic strata.

There is no evidence that Megalosaurus, or [guanodon,
possessed any dermal armor; but several genera (e. g., Sceli-
dosaurus, Hylwosaurus, and Acanthopholis) had osseous
dermal scutes, sometimes produced into prodigious spines.

The faces of the centra of the vertebrz are slightly am-
phiccelous, or nearly flat; but those of the anterior dorsal and
cervical regions seem, in some cases, to have been opisthocce-
lous. The sacrum seems to have consisted of at fewest four
vertebrae, which in some (Scelidosaurus) are crocodilian, in
others (Megalosaurus) take on a somewhat ornithic character.
The caudal region had many and long vertebra, between
which the chevron-bones are attached. The rami of the chey-
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 expanded. 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 Jguwanodon and Hypsilophodon, the extremities of
the premaxillz: appear to have been edentulous and beak-lke ;
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 Megalosaurus, to the broad grinders, wearing
down by mutual attrition, of Jguanodon. 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 VERTEBRATED ANIMALS,

No Ornithoscelidan 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 usually 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 sucha
way that they can hardly, if at all, move on one another. The
inner 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 Ornithoscelida are divisible into two sub-orders, the
Dinosauria and the Compsognatha. The type of the latter
division is the wonderful little extinct reptile, Compsogna-
thus, which differs from the Dinosauria in the great length
of the centra of the cervical vertebre, 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 appears to
have been anchylosed with the tibia, as in birds. A single
specimen only of this reptile has-been obtained, in the Solen
hofen slates.

IX. The PrerosavuriA.—The flying Reptiles, which belong
to this group, and are commonly known as Pterodactyls, 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 vertebree 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 vertebra, apparently not more than six or seven in
number, have low, or obsolete, spinous processes; and, like
the vertebre of the rest of the spine, are procoelous, and
have the neuro-central suture obliterated. The existence of
cervical ribs is doubtful. From fourteen to sixteen vertebra
intervene between the cervical and the sacral regions; and
not more than one or two of the hindermost of them, if any,

Tk PTEROSAURLA. 929

are devoid of ribs, The number of vertebre anchylosed

together to form the sacrum, is not fewer than three, nor more
than six.

Fia. 79.—The nearly entire skeleton of Pterodactylus spectabilis (Yon Meyer), as shows
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 Plerodactylus, and, in this genus,
all the vertebrze are movable upon one another; but in Rham-
phorhynchus, it is extremely long, and the vertebrz 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. The
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. ri

The brain-case is more rounded and bird-like than in the
other Feptilia, 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. The premaxille are
very large, the maxillz 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 lachrymo-nasal fossze between
the orbits and the nasal cavities, and by the prolongation of
the extremities of the premaxillz: and of the symphysial part
of the mandible into sharp, beak-like processes, which appear
to have been covered with 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 aring
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 Carinate. ‘The scapula is slender and
blade-like, and its long axis is mclined, 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
Jevoid of fontanelle, epicoracoid, or procoracoid.

No trace of any clavicle has been discovered.

The humerus has a great deltoid ridge or provess, The
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,
so that these represent the pollex and the succeeding digits

ae

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 Rhamphorhynchus Gemming?, 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, Uones 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 vertebree.

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.
Ornithopterus.
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.

Pterodactylus.

b. The extremities of the jaws produced into toothless beaks,
probably ensheathed in horn. The tailverylong. The meta-
carpus shorter than half the length of the antebrachium,

a, All the mandibular teeth similar.
Lthamphorhynchus.
b. The posterior teeth for the most part very short. The
anterior long.
Dimorphodon.

I am much inclined to suspect that the fossil upon which
the genus Ornithopterus has been founded, appertains toa true

Bird,

CHAPTER VL.

THE CLASSIFICATION AND THE OSTEOLOGY OF BIRDS.

Tue 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 differing 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 Leptilia are indicated.

A. The metacarpals not anchylosed together. The tail longer than the
body.
I.—Savrvurz.
1. Archeopterygide.
B. The metacarpals anchylosed together. The tail considerably shorter
than the body.
a. The sternum devoid of a keel.

II.—RatitZ,

a. The wing with a rudimentary, or very short, humerus and
with not more than one ungual phalanx.
a. A hallux.
2. Apterygide (The Kiwis).
B. No hallux.
3. Dinornithide (The Moas).
4, Casuaride (The Cassowaries).
6. The wing with a long humerus and with two ungual
phalanges.
a. The ischia uniting immediately beneath the sacrum,
and the pubes free.
5. Eheide (The American Ostriches).
; 8. The ischia free and the pubes uniting in a ventral
symphysis.
6. Struthionide (The Ostriches).
B. The sternum provided with a keel.*

* The keel is rudimentary in the singular Parrot Strigopa.

234 THE ANATOMY OF VERTEBRATED ANIMALS.

III. —Carinatz.

a, The vomer broad behind, and interposing between the
pterygoids, the palatines, and the basispheuoidal rostrum

(Dromeognathe.)
7. Tinamomorphe (The Tinamous).

6 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.

(Schizognathe.)
8. Charadriomorphe (The Plovers).
9. Cecomorphe (The Gulls).
10. Spheniscomorphe (The Penguins).
11. Geranomorphe (The Cranes).
12. Turnicimorphe (The Hemipods).
13, Alectoromorphe (The Fowls).
14, Pteroclomorphe (The Sand-grouse),
15. Peristeromorphe (The Pigeons),
16. Heteromorphe (The Hoazin).
ii, The vomer truncated in front.
(_digithognathe.)
17. Coracomorphe (The Passerines).
18. Cypselomorphe (The Swifts).
19. Celeomorphe (The Woodpeckers).

B. The Maxillo-palatines united.

(Desmognathe.)

20. Aetomorphe (The Birds of Prey).
21. Psittacomorphe (The Parrots).
22. Coccygomorphe (The Cuckoos, King-

fishers, Trogons).
23. Chenomorphe (The Anserine Birds).
24. Amphimorphe (The Flamingoes).
25. Pelargomorphe (The Storks).
26. Dysporomorphe (The Cormorants).

* With the exception of Dicholophus and some species of Cran.
+ The subjoined Table, which shows with which of the above groups the
old orders of Birds corr espond, may be useful to the student:

J.—AcciIPiTREs
or = Actomorphe.
Raprores
T7,—Scansorrs . . . . . =Psittacomorphe, Coccygomorphe (in part).
UI. —Passrrus Coracomorphe, Cypselomorphe, Celeomor-
Stans hala aes ~\ phe, Coceygomorphe (in part).

41V.—GALLINz (with Cotumpz) =Alectoromorphe, Peristeromorphe, Pteroclo-
morphe, Tur nicimonph &.

Vi—Curnsornts .... . =Satita.
Vi—Grattme ... + « =Charadriomorphe, Geranomorphe, Amphi-
morphe, Pélargomorphe.
Vll.—Patmirenes .. . «. =Cecomorphe, Spheniscomorphe, Chenomor
phe, Dysporomorphe.

at

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 penne, 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 (scapws) 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 vexdllum, 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 barbs.
The calamus has an inferior aperture (wmbilicus inferior), into
which the vascular pulp penetrates; and a superior aperture
(umbilicus superior) 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 vexi/lum of the feather is horizontal. The inter- -
stices between the barbs are filled up by the darbdules; 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 (hyporachis) 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 Casuaridc, 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 penne, in having the barbs
soft and free from one another, when they constitute penno-
plume, or plumuice (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
Jilopluma.

The contour feathers are distributed evenly over the body
only in a few birds, as the Ratitew, the Penguins, and some
others. Generally, the penne are arranged 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 péerylce, and their interspaces,
apteria.

In some birds, such as the Herons, plumulze of a peculiar
kind, the summits of which break off into a fine dust, or pow-
der, as fast as they are formed, are developed upon certain
portions of the integument, which are termed powder down
patches.

The integument of birds is, for the most part, devoid of
elands; but many birds have a peculiar sebaceous gland
developed in the integument which covers the coccyx. This
uropygial gland secretes an oily fluid, which 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 highly-vascular and sometimes
erectile processes (combs, wattles).

The spinal column of birds contains numerous and well-
ossified vertebree, a considerable number of which (more than
six) are anchylosed together to form a sacrum. Of the verte-
bree 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 vertebrae 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 vertebree, 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 body.

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 odontordeum
is always anchylosed with the second vertebra, and constitutes
a peg-like odontoid process.

The spines of the succeeding cervical vertebrz 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

“ae

‘
i
:
;

THE VERTEBRA IN BIRDS. 237

are convex from above downward, and concave from side to
side. Hence, in vertical section, the centra appear proccelous ;
in horizontal section, opisthoccelous; and this structure is ex-
ceedingly characteristic of birds. The under surfaces of the
centra frequently give off median inferior processes. In the
Ratitce, it is obvious that the cervical vertebrae 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
aud a lower; and the expanded head of a styliform rib is ar-
ticulated with 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 Oarinatw; 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 vertebrae become elongated and freely movable in the
Carinate, as in the Ratite.

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 vertebrze (reckoning under that
head all the vertebrz, after the first dorsal, which possess dis-
tinct ribs, whether they be fixed or free) varies. The centra
of the dorsal vertebra 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 vertebrs of Birds that the
posterior, no less than the anterior, vertebre present a facet,
or small process, on the bedy, 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 vertebree 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 vertebrz
of Crocodilia, Dinosauria, Dicynodontia, and Pterosauria.
The discrimination of the proper lumbar, sacral, and ante-
rior caudal vertebre, in the anchylosed mass which constitutes
the so-called “sacrum” of a bird, is a matter of considerable

Fig. 80.—The “Sacrum” cfa Chick. d., dorso-lumbar; 8., sacral; ¢., caudal vertebra.

difficulty. The general arrangement is as follows: The most
anterior jumbar 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
vertebree this 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 vertebrze in other Vertebrata. 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 vertebrze unite to

* It would be more proper to say that ossification extends into it from the
centrum as well as from the neural arch. The process, like other processes.
exists before the centrum is differentiated from the arch by ossification.

te

THE VERTEBRA IN BIRDS. 939

form the sacral plexus, whence the great sciatic nerve is given
off; and I take them to be the homologues of the sacral ver-
tebree of Leptilia, ‘The deep fossz between the centra of these
vertebra, their transverse processes, and the ilia, are occupied
by the middle lobes of the kidneys.

If these be the true sacral vertebre, it follows that their
successors are agterior caudal. They have expanded upper
transverse processes, like the proper sacral vertebrze ; but, in
addition, three or four of the most anterior of these vertebree
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 vertebrae, while, distally,
they expand and abut against the ilium. The anchylosed
caudal vertebrae may be distinguished as wrosacral. The
caudal vertebrze which succeed these may be numerous and all
distinct from one another, as in Archcopteryx and Rhea ; but,
more generally, only the anterior caudal vertebrie are distinct
and movable, the rest being anchylosed into a plough-share
shaped bone, or pygostyle, which supports 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 vertebre of Birds
are connected together by fibro-cartilaginous rings, which
extend from the circumference of one to that of the next.
Kach 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
vertebre. In the caudal region, the union is complete, and
the meniscus altogether resembles an ordinary intervertebral
cartilage.

A ligament traverses the centre of the aperture in the
meniscus; and, in the chick, contains the intervertebral por-
tion of the notochord. As Jiiger* 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 Mammalia.

*‘*Das Wirbelkérpergelenk der Végel.’? Sitzungsberichte der Wiener
Akademie, 1858.

240 THE ANATOMY OF VERTEBRATED ANIMALS.

All the vertebral ribs in the dorsal region, except, perhaps,
the very last free ribs, have widely-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 replaced
in the adult by membrane-bone.* It begins to ossify by, at
fewest, two centres, one on each side, as in the Ratite. In
the Carinate 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 (7. to m. x. in Fig. 81) is termed
the lophosteon, the antero-lateral piece which articulates with
the ribs, pleurosteon (pl. o.),and the posterolateral bifurcated
piece, metosteon.

Though the sternum, in most birds, seems to differ very
much in form from that of the Septilia, it is rhomboidal in
the Casuaride, where it differs 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 Carinate, the antero-lateral edges, which are grooved
to receive the coracoids, form a much more open angie than
in the Jeptilia, while the postero-lateral edges become
parallel, or diverge ; and a wide, straight, or convex, transverse
edge takes the place of the posterior angle. Two, or four,
membranous fontanelles may remain in the posterior moiety
of the sternum when ossification takes place, and give rise to
as many holes, or deep notches, separating slender processes
in the dry skeleton. All these correspond with so many divis-
ions of the xiphoid process of the sternum in Mammalia, and
hence are called middle, internal, and external xiphoid pro-
cesses. Sometimes, a median process, rostrum or manubrium
(r., Fig. 81), is developed from the anterior angle of the ster-
num, and its antero-lateral angles are frequently produced into
costal processes (c. p., Fig. 81), which may bear the articular
surfaces for more or fewer of the ribs. The two last-named
structures are very distinct in the Coracomorphe, or Passerine
Birds.

* These statements respecting the vertebral column, ribs, and sternum,
like those further on touching the skull, do not apply to Archwopteryx, in
which all these parts are unknown or imperfectly known.

THE STERNUM IN BIRDS. 241

The extent to which the keel of the lophosteon is devel-
oped in the carinate birds varies very much. In Sérigops it
is rudimentary ; in birds of powerful flight, as well as in those

which use their wings for swimming, it 1s exceedingly large.

H
H
=
=
S
=
=
=~
SS
SS
——

a
'

)

yh

i)

Fia. 81.—Front and side views of the sternum ofa Fowl. 7., rostrum, or manubrium: ¢. p,
costal process; /. 0., pleurosteon (the line from the letter goes to the point of juno-

tion between the pleurosteon and the metosteon); m. @., the middle xiphoid process ;
ca., the carina or keel.

In the bird’s skull (Fig. 82), the brain-case is more arched
and spacious, and is larger, in proportion to the face, than in
any Lteptilia, with the exception of the Prerosauria. There
is a well-marked interorbital septum, but the extent to which
it is ossified varies greatly. As a general rule, the superior
temporal bar is incomplete, and there is no distinct post-frontal
bone. The inferior temporal bar, formed by the jugal and
quadrato-jugal, on the other hand, is always complete. There
are no long parotic processes, nor any post-temporal fosse,
the whole of each parietal bone being, as it were, absorbed in
the roof of the skull.

The nasal apertures are almost always situated far back

near the base of the beak. In the dry skull (above JZ. in
1

942 THE ANATOMY OF VERTEBRATED ANIMALS.

Fig. 82), there is a lachrymo-nasal fossa, or interval unoccupied
‘by bone, between the nasal, lachrymal, and maxillary bones,
such as exists in some Zéleosauria, Dinosauria, and Ptero-
sauria.
_ The posterior nares lie between the palatines and the
vomer; and the nasal passage is never separated from the
cavity of the mouth by the union of palatine plates of the
palatine or pterygoid bones.

The Eustachian tubes generally traverse the basisphenoid,
and have a common aperture upon the middle of the under
surface of the skull.

Fig. 82.—-Lateral, upper, and under views of the skull of a common Fow] (Phasianus gat.
see maxp., the maxillo-palatine process. Quw., the quadrate bone. The dotted line
accidentaily stops at the angular process of the mandible.

The bones of the brain-case, and most of those of the face,
very early become anchylosed together into an indistinguish-

THE SKULL IN BIRDS. 243

able whole in most birds, but the sutures remain distinguish-
able longer in the Chenomorphe and Spheniscomorphe ; and
especially in the Ratite.

All the constituents of the occipital and parietal segments
of the skull are represented by distinct bones, but the frontal
segment varies a good deal in this respect. The basisphenoid
has a long rostrum, which represents part of the parasphenoid
of the Lchthyopsida. Large frontal bones always exist, but
the pre-sphenoidal and orbito-sphenoidal regions are not so
regularly ossified.

The ethmoid is ossified and frequently appears upon the sur-
face of the skull, between the nasal and the frontal bones; and
the internasal septum, in front of the ethmoid, may present
very various degrees of ossification. Very frequently, the in-
terspace between the ethmoidal and the internasal ossifications
is simply membranous in the adult, and the beak is held to the
skull only by the ascending processes of the premaxillary
bones, and by the nasal bones, which are thin and flexible.
By this means a sort of elastic joint is established, conferring
upon the beak a certain range of vertical motion. In the Par-
rots, and some other birds, this joint is converted into a true

Causey aD

Fie. 83.—A longitudinal and vertical section of the posterior half of the skull of an Ostrich
P., the pituitary fossa; asc., psc., anterior and posterior vertical semicircular canals of
the ear.

articulation, and the range of motion of the upper beak be:
comes very extensive.
The periotic capsule is completely ossified, and, as in other

944 THE ANATOMY OF VERTEBRATED ANIMALS.

Sauropsida, the epiotic and the opisthotic are anchylosed
with the occipital segment before they unite with the prodtic.
In the primordial skull of the bird the olfactory organs are
surrounded by cartilaginous capsules, the lateral walls of which
send in turbinal processes of very various degrees of complex-
ity. When the posterior wall of this capsule is ossified, the
bone thus formed represents the prefrontal, or lateral mass of
the ethmoid, of the mammal. It is largely developed in the
Apteryx, in the Casuaride, and many other birds, but is ab-
sent in the Struthionide ; and, in other birds, is often repre-
sented by a mere bar of bone standing out from the ethmoidal
ossification.

The lachrymal is, usually, a distinct and large bone articu-
lated with the nasal and frontal above, with the prefrontal
internally, and with the maxilla below; but sometimes it be-
comes undistinguishably fused with the prefrontal. Some-
times, on the contrary, as in the Parrots, it acquires a large
size, and sends a process backward beneath the orbit, which
may join with a post-orbital process of the frontal, and so cir-
cumscribe the orbital cavity. Opisthocomus exhibits the pe-
culiarity of the complete anchylosis of the nasal with the
lachrymal, which is quite free from the frontal and moves with
the hinged beak. A supra-orbital bone, or chain of bones,
may be developed in connection with the orbital margin of the
frontal bone; and, occasionally, infra-orbital bones appear be-
low the orbit, parallel with the jugal arch. A post-orbital
process may be developed from the frontal, or from the ali-
sphenoid; and, in the latter case, may be separately ossified.

The squamosal is closely applied to the skull, and is, usual-
ly, anchylosed with the other bones. It often sends a process
downward over the quadrate bone, and it may be united by
bone with the post-orbital process of the frontal, as in the
Fowl.

The frame of the tympanic membrane not unfrequently
contains distinct ossifications, which represent the tympanic
bone of the Mammalia.

The premaxillze are modified in a manner which finds a
partial parallel only among the Fteptilia. They are tri-radiate
bones of great size, which, usually, give off three processes ;
an ascending process to the frontal; a palatine process, along
tne middle of the palate, to the palatine bones; and an exter-
nal, or maxillary process, which forms the greater part of the
margin of the beak, and unites with the maxilla. The two bones
are very early represented by one continuous ossification.

pS Sern *

as

THE SKULL IN BIRDS. 245

The vomers vary more than almost any other bones of the
skull, They underlie and embrace the inferior edge of the
ethmo-presphenoidal region of the basis cranii, and, in all
birds in which they are distinctly developed, except the Os-
trich, they are connected behind with the palatine bones. In
most birds, they early unite into a single bone; but they
remain long distinct in some Coracomorphe, and seem to be
always separate in the Woodpeckers. The coalesced vomers
constitute a very large and broad bone in most Aatiiw, and in
the Zinamomorphe ; a narrow elongated bone pointed in
front in Schizognathe ; a broad bone deeply cleft behind, and
abruptly truncated in front, in Coracomorphw. In most Des-
mognathe the vomer is small; and, sometimes, it appears to
be obsolete.

The maxille of birds are usually slender, rod-like bones,
articulating by squamous suture, in front, with the premaxille,
and, behind, with the equally slender jugals. In the great
majority of birds the maxilla sends inward a mazillo-palatine
process (Fig. 82, map.), which, sometimes, is mere thin lamel-
la of bone, sometimes, becomes swollen and spongy. In the
Ratite and the Desmognathe (Fig. 84), the maxillo-palatine
processes unite with the vomer, or with one another, and form

Fia. 84.—The under surface of the cranium of the Secretary bird (@ypogeranus), 28 an ex:
ample of the Desmognathous arrrangement. J/ap., maxillo-palatine process; Lpt., baai
pterygoid processes,

246 THE ANATOMY OF VERTEBRATED ANIMALS.

a complete bony roof across the palate. In the Schizognathe
(Fig. 82), and dgithognathe, the maxillo-palatines remain
quite distinct both from one another and from the vomer.

The quadrato-jugal is usually a slender rod of bone, the
hinder extremity of which presents, on its inner side, an artic-
ular head which fits into a fossa in the outer face of the distal
end of the quadrate bone.

The palatine bones are generally long and concave on their
palatine faces. In front, they pass beneath (i. e., on the ven-
tral side of) the maxillo-palatines and unite with the premax-
ill, sometimes by a squamous suture, sometimes by anchy-
losis, rarely, as in the Parrots, by a flexible joint. Posteriorly,
they always unite with the pterygoids. In most birds, the
palatines converge, posteriorly, toward the basi-sphenoidal
rostrum, and unite with it by an articular surface, which allows
of a sliding motion of the palatines upon the rostrum. Such
an articulation does not exist in fatite, or in the Tinamous,
among the Carinate. In these (with the exception of
Struthio), the palatines are, as it were, borne off from the ros-
trum by the divergent ends of the great vomer, and the dispo-
sition of the parts is more lacertilian than in other birds,
The outer, or posterior, end of the pterygoid bone presents a
fossa for an articular head, which is developed upon the inner
side of the distal end of the quadrate. The inner, or anterior,
ends of the pterygoids meet in almost all birds, and may be-
come articulated with the basi-sphenoidal rostrum. In all em-
bryonic birds, in all the Ratite, and in many Carinate, such °
as the Zinamomorphe, Charadriomorphe, Alectoromorphe,
Peristeromorphe, Chenomorphe, longer or shorter processes
extend from the basi-sphenoid, and present terminal articular
facets to corresponding facets upon the inner sides of the
pterygoids. These are basi-pterygoid processes, similar to
those which occur in Lacertilia and some Ophidia.

The quadrate bone is almost always movable upon the
skull, articulating with the prodtic, alisphenoid, and squamo-
sal, by a single, or double, head. ‘The distal head articulates
with the mandible below, the quadrato-jugal on the outer, and
the pterygoid on the inner, side. Hence, when the ethmo-
nasal joint is developed, any forward movement of the distal
end of the quadrate, such as must take place when the mandi-
ble is depressed by the digastric muscle, causes the maxillo-
jugal bar to thrust the premaxilla upward and forward; the
palatine and pterygoid bones, at the same time, sliding for-
ward upon the rostrum of the basisphenoid. Thus it comes

i

THE PECTORAL ARCH IN BIRDS. 247

about that the upper jaw of such a bird asa Parrot rises, when,
in opening the mouth, the mandible is depressed. Each ramus
of the mandible consists primitively of six pieces, as in other
Sauropsida, but the dentary pieces of each side are, as in the
Chelonia, very early united, if indeed they are not ossified
from one centre. Very often, a fontanelle remains between
the dentary and the other elements, as in Crocodilia ; and
the dentary long remains readily separable from the rest; or,
as in the Goatsuckers, is united with the others only by fibrous
tissue, so that it is movable. The angle of the mandible may
be truncated or produced backward into a long curved pro-
cess, as in Fowls (Fig. 82), Ducks, and Geese.

The hyoid is composed of basal elements, the anterior of
which, usually composed of two portions, lies in the tongue ;
and of two short, anterior, and two long, posterior, cornua,
which are never united with the periotic region of the skull,
and commonly remain quite free. In some of the Wood-
peckers, however, the long posterior cornua are immensely
elongated, and curved upward and backward over the skull
(the frontal bones being grooved to receive them), and their
free ends are inserted between the ascending and maxillary
processes of the right premaxilla,

The pectoral arch presents a long, narrow, and recurved
scapula (Sc. Fig. 843), without any suprascapula; and a cora-
coid ( Co.), fitted by its proximal end into the groove in the
antero-lateral edge of the sternum. The inner ends of the
coracoids occasionally overlap, as in Lacertilia ; otherwise, the
shoulder-girdle is unlike that of any of the Reptilia, except the
Pterosauria. The coracoid is usually completely ossified, and

Fie. 843 —The right scapula (Sc.) and coracoid (Co.) of a Fowl: gi, the glenoidal cavity;
f, the right clavicle, or right half of the furculum ; 2p, the hypocleidium,

248 THE ANATOMY OF VERTEBRATED ANIMALS,

presents no fontanelle. There is no distinct epicoracoid, The
two bones take nearly equal shares in the formation of the
glenoidal cavity, and usually remain unanchylosed and distinct
in this region.

In the fatite the long axis of that part of the scapula
which lies near the glenoid cavity is parallel or coincident with
that of the coracoid, and the two bones become completely
anchylosed. But, in all the Carinate, the long axis of the
scapula forms an acute, or only slightly obtuse angle ( Ocydro-
mus, Didus) with that of the coracoid. A small bone, the
scapula accessoria, is developed on the outer side of the shoul-
der-joint in most Coracomorphe and Celeomorphe.

In the Carinate, the glenoidal end of the scapula is divided
into two portions ; a glenoidal process, which expands to form
the upper part of the glenoidal cavity, and to unite with the
coracoid, and an acromial process, which gives attachment to
the outer end of the clavicle. The glenoidal end of the cora-
coid is in like manner divided into two portions; a glenoidal
process, which unites with the scapula, and a clavicular process,
which articulates with the outer surface of the clavicle, near
its outer end.

The clavicular process of the coracoid probably represents
the procoracoid of Lacertilia. In the Aatite there is no dis-
tinct clavicular process, but the anterior part of the coracoid,
near the glenoid cavity, may be produced and separated by a
notch, or fontanelle, from the rest, as a lacertilian procoracoid.
There is no trace of clavicles in the Apteryx and in some Par-
rots. In the Emeu, and in sundry Carinate (some Parrots
and Owls), the clavicles remain distinct from one another, or
connected only by fibrous tissue ; but, in the majority of birds,
they are very early anchylosed together, and with the repre-
sentative of the interclavicle, in the middle line, into a single
bone, the furculum, the strength of which bears a pretty close
relation to the exertion required of the wings in flight, or in
natation. In the passerine birds the scapular end of the clav-
icle is usually expanded, and ossifies separately, as an epicle?-
dium. A median process (hypocleidium) is frequently devel-
oped from the interclavicular part of the furculum, and this
may be united with the carina of the sternum by strong fibrous
tissue, or even by continuous ossification. In Opisthocomus,
the furculum is anchylosed with the manubrial part of the ster-
num, on the one hand, and with the coracoids on the other.
Anchylosis of the fureulum with the coracoids has also been
observed in Didus.

—e- ee he,

SR SER EES Se eee

THE FORE-LIMB IN BIRDS. 249

The fore-limb of a bird, when in a state of rest, exhibits a
great change of position if it be compared with that of an or-
dinary reptile; and this change is of a character similar to,
but in some respects greater than, that which the arm of a man
presents, when compared with the fore-limb of a quadrupedal
mammal, The humerus lies parallel with the axis of the body,
its proper ventral surface looking outward. The forearm is in
a position midway between pronation and supination, and the
manus is bent back upon the ulnar side of the forearm, in a
position, not of flexion, but of abduction.

In ordinary birds, the proximal end of the humerus is ex-
panded, and its articular head transversely elongated ; its ven-
tral face is convex, and provided with a strong preaxial ridge,
which gives attachment to the pectoral muscle. The proper
dorsal face is concave from side to side, especially toward the
postaxial margin, where the pneumatic aperture occurs in those
birds which have the humerus hollow. The distal end is ex-
panded, and the articular surface for the radius is a convex
facet, directed obliquely inward, on its ventral face. In this
respect the bird’s humerus exaggerates a feature of that of the
Lizards.

In the Ratite these peculiarities are very feebly, or not at
all, marked, the humerus being a slender, cylindrical, slightly-
curved, bone. In the Casuaride, Dinornithide, and Aptery-
gide, the fore-limb is extraordinarily reduced, and may become
rudimentary. In the Penguins and, to a less degree, in the
great Auk, the humerus becomes flattened from side to side ;
the proximal end is singularly modified, and, at the narrow
distal end, the articular surface for the radius lies completely
in front of, and rather above, that for the ulna.

The ulna, which often presents a series of tubercles, indi-
eating the attachment of the secondary quill-feathers, is usu-
ally a stronger, and a longer, bone than the radius. There are
only two carpal bones, one radial and one ulnar.

In the Apterygide and in the Casuaride, there is but one
complete digit in the manus. It appears to answer to the
second of the pentadactyle limb, and is provided with a claw.
In the Struthionide and Rheide, and in all Carinate, there
are three digits in the manus, which answer to the pollex and
the second and third digits of the pentadactyle fore-limb; and
the metacarpal bones of these digits are anchylosed together.
As a rule, the metacarpal of the pollex is much shorter than
the other two; that of the second digit is strong and straight,
that of the third is more slender and bowed, so as to leave an

350 THE ANATOMY OF VERTEBRATED ANIMALS.

interspace between itself and the second, which is often filled
up by bony matter. The pollex has two phalanges, and the
second of them is, in many birds, pointed, curved, and en-
sheathed ina horny claw. The second digit
has three phalanges, and the terminal pha-
lanx is similarly provided with a claw in sun-
dry birds. In the ostrich, both the pollex
and the second digit are unguiculate. The
third digit never possesses more than one or
two phalanges, and is always devoid of a
claw.

It is a singular circumstance that the
relative proportions of the humerus and the
manus should present the most marked con-
trast in two groups of birds, which are alike
remarkable for their powers of flight, These
are the Swifts and Humming-birds, in which
the humerus is short and the manus long ; and
the Albatrosses, in which the humerus is long
and the manus relatively short.

In the Penguins, the pollex has no free
phalanges, and its metacarpal bone seems to
be anchylosed with that of the second digit.
The third metacarpal is slender and straight.
The bones of the manus are singularly elon-
gated and flattened.

The pelvis of a bird (Fig. 86), is remark-
| able for the great elongation, both anteriorly
Fig. 85.—The rads (r); and posteriorly, of the iliac bones (JZ),

war oorbal hoaes ’, Which unite with the whole length of the
uw); with the three di- edges of the sacrum (Sm.) and even extend
Feo or forward over the posterior ribs of the dor-
Fowl. The terminal ga] region. Below, each iliac bone forms a
phalanges of both the : 5
first and the second di- Wide arch over the upper part of the acetab-
Phe specimen figurea, Ulum (Am.), the centre of which is alway
closed by fibrous tissue, so that, in the dry
skeleton, the bottom of the acetabulum is perforated by a wide
foramen, An articular surface on the ilium, on which the
great trochanter of the femur plays, is called the antitrochanter.
In all ordinary birds, the ischium (Fig. 86, Zs.), which broad-
ens toward its hinder end, extends back, nearly parallel with
the hinder part of the ilium, and is united with it by ossifica-
tion, posteriorly. The iliosciatic interval is thus converted into
» foramen. The pubis (P0.) enters, by its dorsal or acetabular

THE PELVIS IN BIRDS. 251

end, into the formation of the acetabulum, and then passes
backward and downward as a comparatively slender, curved,
bone, nearly parallel with the ischium, It is united with its

\ SS
ZS
BRAN

\

SS

Fie, 86.—A, lateral; and B, dorsal, view of the pelvis of a Fowl. Sm., sacrum; J1., ilium
Js., ischium; Pd., pubis ; Am., acetabulum.

fellow only by fibrous tissue. Neither the ischia, nor the pubes,
unite directly with the sacrum. Very few birds present any
important deviation from this structure of the pelvis. In Z7%-
namus, Casuarius, Dromaus, Apteryx, Dinornis, the ischium
is not united with the backward extension of the ilium by bone.
In Rhea, the ischia unite with one another beneath the verte-
bral column, and the vertebree in this region are very slender
and imperfectly ossified. In Struthio, alone, among birds, do

252 THE ANATOMY OF VERTEBRATED ANIMALS.

the pubes unite in a median ventral symphysis. Another, not
less remarkable circumstance, in the ostrich, is, that the 31st
to the 35th vertebrze inclusively (counting from the atlas) de-
velop five lateral tuberosities. ‘The three middle tuberosities
are large, and abut against the pubis and the ischium, In
these vertebrze, as in the dorsal vertebrz of Chelonia, the neu-
ral arch of each vertebra shifts forward, so that half its base
articulates with the centrum of the next vertebra in front; and
the tuberosities in question are outgrowths, partly of the neu-
ral arch, partly of the juxtaposed vertebral centra, between
which it is wedged. Hence, in young ostriches, the face of
each tuberosity exhibits a triradiate suture.

The upper articular head of the femur is rounded, and its
axis is almost at right angles with the body of the bone; a
structure which is not found in ordinary feptilia, but exists in
the Lguanodon and other Ornithosce-
, lida. he shaft is relatively short and
1) thick, and the two terminal condyles are
large and elongated antero-posteriorly.
A prominent ridge, which plays be-
tween the proximal ends of the tibia
and the fibula, is apparent upon the
posterior and inferior surface of the
outer condyle. A similar ridge is
faintly developed in some JLacertilia,
and is well marked in the Dinosaurian
reptiles. A patella is usually present,
but it is sometimes absent, and may be
double.

The fibula of birds is always imper-
fect, ending in a mere style below.
Generally it is decidedly shorter than
the tibia, but it has the same length as
that bone in some Penguins, The tibia,
or rather tibio-tarsus, is a highly-char-
‘acteristic bone. Its proximal end is
expanded and produced anteriorly, into
a great cnemial process (which may be

A
F a. 87.—The right tibia and
fibula of a Fowl. A, front
view; b. external lateral
view. T., tibia; F., fibula;
On., eremial process; As.
astragalus.

variously subdivided) as in Dinosauria.
The distal end is terminated by a well-
marked, pulley-like, articular surface
which is inclined somewhat forward as
well as downward. Not unfrequently

there is an oblique bar of bone on the anterior face, just above
the pulley, beneath which the long extensor tendons pass.

THE HIND-LIMB IN BIRDS. 953

The extremity of the cnemial process in Struthio and Rhea
is ossified as an epiphysis ; and, in young birds, the whole of
the distal articular end of the bone is separated from the rest
by a suture, and also appears to be an epiphysis. But it is,
in fact, as Prof. Gegenbaur has proved, the proximal division
of the tarsus (apparently representing only the astragalus of
the other Vertebrata), which exists in the embryo as a separate
cartilage, and, as it ossifies, anchyloses with the tibia. The
so-called tibia of a bird is therefore, properly speaking, a ¢ibto-
tarsus (see p. 226, Fig. 87, A, and Fig. 88). .

In all birds, even in Archeopteryx, the fifth digit of the
pes remains undeveloped; and the second, third, and fourth
metatarsals are anchylosed together, and, by their proximal
ends, with a bone, which is a distinct cartilage in the foetus,
and represents the distal division of the tarsus. Thus a farso-
metatarsus is formed, The distal ends of the metatarsals re-
main separate, and offer convex articular surfaces to the proxi-
mal phalanges of the digits.

Fic. 88 —The distal end of the Fig. 89.—The right tarso-metatarsus
ieft tibia (76.) with the of a Fowl, consisting of three
astragalus (As.) detached, digits, ii., lii., iv., anchylosed with
of a young Fowl. Viewed one another, and with tbe osseous
from in front, and from the core of the spur. A., front aspect;
outer side. B., inner aspect.

In the Penguins, large apertures lie between the several
metatarsals of the adult tarso-metatarsus ; and, in other birds,
more or less considerable passages persist between the middle
and the lateral metatarsals proximally, and the middle and the

254 THE ANATOMY OF VERTEBRATED ANIMALS.

outer, distally. In most birds, the middle metatarsal does not
remain parallel with the others, but its proximal end inclines
a little backward, and its distal end a little forward. Hence
the two apertures on each side of its proximal end may lie at
the bottom of a fossa, or run into one, in front, while they
remain distinct behind.

Again, in most birds, the posterior face of the proximal
end of the middle metatarsal, and the adjacent surface of the
tarsal bone, grow out into a process, which is commonly,
but improperly, termed “calcaneal.” The inferior surface
of this hypo-tarsus is sometimes simply flattened, sometimes
traversed by grooves or canals, for the flexor tendons of the
digits,

When a hallux exists, its metatarsal bone is usually in-
complete above, and is united by ligament to the inner, or the
posterior, surface of the tarso-metatarsus. In the Frigate-bird
(Phaethon) and in Steatornis, the hallucal metatarsal is re-
markably long. The genus Phaethon stands alone, so far as
I know, in having the hallucal metatarsal anchylosed with the
others.

In many of the Alectoromorphe, a spur (calcar), consisting
of a bony core ensheathed in horn, is developed on the inner
side of the metatarsus, and becomes anchylosed with the meta-
tarsal of the second digit. Ina few birds, similar spurs (Lala-
medea), or osseous excrescences (Pezophaps), are developed
in relation with the metacarpus.

The normal number of the pedal phalanges in birds is (as
in ordinary Lacertilia) 2, 3, 4, 5, reckoning from the hallux to
the fourth digit. Among the few birds which constitute ex-
ceptions to the rule are the Swifts, in which the third and
fourth toe have only three phalanges each (2, 3, 3, 3), and the
Goatsuckers and the Sand-grouse, in which the fourth toe
only has the number thus reduced (2, 3, 4, 3).

Many birds have only three toes, by suppression of the
hallux. In the Ostrich, not only the hallux, but the phalanges
of the second digit, are suppressed; and the distal end of the
second metatarsal is reduced to a mere rudiment. Hence the
ostrich has only two toes (which answer to the third and fourth
of the pentadactyle foot), with four phalanges in the inner and
five in the outer, though the inner toe is far the longer and
the stronger.

In most four-toed birds the hallux is turned more or less
completely backward, and the other three digits forward. But
in many Aectomorphe (especially the Owls), the outer toe can

eee ee ee

THE FOOT IN BIRDS. PAT

be turned outward, or even backward, at will. And in the
Parrots, Toucans, Cuckoos, Woodpeckers, and other so-called
‘“‘scansorial” birds, the outer toe is permanently reversed.
Under these circumstances the distal end of the outer meta-
tarsal may be divided into two distinct articular surfaces. In
the Trogons, there are two toes in front and two behind, as
in the Parrots, but it is the second toe which is turned back-
ward. Lastly, in the Swifts, the Dysporomorphe and the
Spheniscomorphe, the hallux is directed more or less forward,
so that all four toes are turned to the front.

As a general rule, the osseous tissue of birds is remarkably
dense and hard. Before hatching, the bones are solid and
filled with vascular medulla; but, after birth, more or fewer
of the bones are always excavated by prolongations of cavities
containing air, which lie in their neighborhood. Such air-
cavities are always found in the skull, in connection with the
nasal and auditory passages, and they may extend through all
parts of the skull, with the exception of the jugal arch. In
many birds, such as the Apteryx, Penguins, Divers, Gulls, and
the smaller song-birds, no other bones than those of the skull
are pneumatic; but, in most birds, the air-sacs of the lungs
send off prolongations into the bones of the rest of the skele-
- ton, and thus the whole skeleton in some cases (as in the
Hornbills) becomes pneumatic. It is proper to remark that
the amount of pneumaticity of the bones by no means follows
the development of the power of flight. In the Ostrich, for
example, the bones are far more extensively pneumatic than
in the Gull,

In some cases, prolongations of the air-sacs extend beneath
the integument.

CHAPTER VII.
THE MUSCLES AND THE VISCERA OF THE SAUROPSIDA.

Tue most important deviations from the ordinary arrange-
ment of the muscular system occur, as might be expected, in
the Ophidia, in the Chelonia, and in Aves. In the first-men-
tioned group, the numerous muscles of the limbs are, of course,
absent, and the mobility of the vertebra, ribs, and jaws, is ac-
companied by a corresponding differentiation of the muscles
of those parts. The episkeletal muscles form a continuous
series (divisible into spinalis, semispinalis, longissimus dorsi,
levatores costarum, and other muscles) from the end of the tail
to the head; and, in the region of the back, constitute a thick
mass which extends outward to the ends of the caudal ribs
(the so-called transverse processes), and over the dorsal thirds
of the other ribs. Beyond these points it is continued, as a
thinner layer of muscular fibres, over the ventral half of the
tail and trunk, passing from rib to rib in the latter region,
where the more dorsal fibres are directed obliquely, only a
longitudinal band running along the extremities of the ribs
and representing a rectus abdominis. This muscle is contin-
ued forward to the hyoidean apparatus, and thence to the
mandible. Superficial muscular bundles pass from the ribs to
the scales. The hyposkeletal muscles are better developed
than in most other Vertebrata, and also extend from the head
vo the end of the tail. A median dorsal set are connected with
the subvertebral processes in the trunk, and with the bases of
the representatives of the chevron-bones in the tail, and pass
to the caudal and dorsal ribs. One set of these, in the trunk,
act as retractors of the ribs. The muscles which correspond
with the transversus abdominis commence in the tail by trans-
versely-directed bundles of fibres, which arise from the roots
of the caudal ribs (transverse processes), and meet in a median

ie ee ode

Fe ee ee ee ee ae ‘

MUSCLES OF THE SAUROPSIDA. 257

aponeurosis. In the trunk, similar bundles arise from the
under surfaces of the ribs, and form two layers of oblique fibres,
which also meet in the middle line.

In the Chelonia, the episkeletal muscles are always weakly
developed, and may be altogether abortive in the dorsal region,
while those of the abdominal walls are small. The rectz are
very weak, but muscles answering to the pyramidales extend
from the pubes to the inner surface of the plastron. A mus-
cular expansion analogous to a diaphragm may be attached to
the bodies and ribs of ‘the third and fourth dorsal vertebre,
whence it expands over the surface of the lungs. No muscles
pass from the head to the shoulder-girdle. The pectoral arch
is protracted, and the neck retracted, by a muscle attached to
the cervical vertebrz and to the procoracoid. There is also a
single retractor of the pectoral arch, apparently representing
a serratus magnus, and passing from the first costal plate to
the scapula. The pectoralis major arises from the inner sur-
face of the plastron. The representative of the latissimus dor-
sé arises from the inner side of the first costal plate.

The cutaneous muscles of birds are well developed, and
form broad expansions in various parts of the body. Special
bundles of muscular fibres pass to the great quill-feathers of
the tail and wings, and others to the patagium, a fold of in-
tegument which extends between the trunk and the brachi-
um behind, and between the brachium and ante-brachium in
front. In correspondence with the slight mobility of the dor-
sal vertebrae, the episkeletal and hyposkeletal muscles of the
spine attain a considerable development only in the neck and
in the tail. Owing to the great size of the sternum, the ab-
dominal muscles are usually small, and the internal oblique
may be absent. A diaphragm, consisting of bundles of mus-
cular fibres, which pass from the ribs to the aponeurosis cover-
ing the ventral face of the lungs, is developed in all birds, but
attains the greatest degree of completeness in the fatite, and
especially in Apterya.

The muscles of the limbs are remarkably modified by the
excessive development of some of those found in other Verte-
brata, and the suppression of others.

Thus in all birds possessing the power of flight, the pee-
toralis major, as the chief agent of the dow nward stroke of
the wing, is very large and thick, taking its origin from the
whole length, and a great part of the depth, of the keel of the
sternum.

258 THE ANATOMY OF VERTEBRATED ANIMALS.

The elevation of the wing is chiefly effected by the pecto-
ralis tertius, which arises beneath the foregoing muscle, and
passes over the inner side of the scapulocoracoid articulation,
as over a pulley, to reach the humerus. The muscles of the
forearm and digits are reduced, in accordance with the pecul-
lar modification of the skeleton of these paris. In the hind-
limb of most birds there is a singular extensor muscle, which
arises from the pubis, ends in a tendon which passes to the
outer side of the knee-joint, and terminates in the leg by unit-
ing with the flecor digitorum perforatus. The result of this
arrangement is, that the toes are flexed whenever the leg is
bent upon the thigh, and, consequently, the roosting bird is
held fast upon his perch by the weight of his own body.

In all the Sauropsida the cerebro-spinal axis is angulated
at the junction of the spinal cord with the medulla oblongata,
the latter being bent down toward the ventral side of the
body. The region in which the nerves of the anterior and
posterior extremities originate may be enlarged in reptiles, as
in birds; but, in the former, the posterior columns of the cord
remain parallel in the lumbar enlargement, while, in the lat-
ter, they diverge and give rise to the sinus rhomboidalis,
which is a sort of repetition of the fourth ventricle, the dilated
central canal of the spinal cord being covered merely by a
thin membrane consisting chiefly of the ependyma and arach-
noid.

The brain (Fig. 90) fills the cavity of the skull in the
higher Sauropsida, and presents a well-developed cerebellum ;
a mesencephalon divided above into two optic lobes; and
relatively large prosencephalic hemispheres, which attain a
considerable size in Crocodilia and Aves, but never conceal
the optic lobes. In Crocodilia the cerebellum presents a dis-
tinct vermis, with transverse fissures. In birds the latter are
more distinct, and the lateral appendages of the cerebellum,
or fiocculi, become well defined, and are lodged, as in man
of the lower Mammalia, in cavities of the side walls of the
skull, arched over by the anterior vertical semicircular
canal.

There is no pons Varolii, in the sense of transverse fibres
connecting the two halves of the cerebellum, visible upon the
ventral surface of the mesencephalon. The optic lobes con:
tain ventricles. In Leptilia, the optic lobes usually lie close
together upon the dorsal side of the mesencephalon, but in
Aves (Fig. 90 B, D) they are thrown down to the sides of the

NEUROLOGY OF THE SAUROPSIDA. 259

Fic. 90.—A, C, the brain of a Lizard (Psammosaurus Bengalensis), and B, D, ofa bird
(Meleagris gallopavo, the Turkey), drawn as if they were of equal lengths. A, B,
viewed from above; C, D, from the left side. OJf, Olfactory lobes; Pn., Pineal gland;
Hmp., cerebral hemispheres; J£0., optic lobes of the mid-brain; Cd., cerebellum; JZ.
O., medulla oblongata; @., zv., vi., second, fourth, and sixth pairs of cerebral nerves;
Py., pituitary body.

base of the brain, and are connected over the aquceductus
Sylvit by a broad commissural band.

Each prosencephalic lobe contains a lateral ventricle (con-
tinuous through the foramen of Munro with the third ven-
tricle), which is little more than a fissure between the very
thin inner wall of the lobe and its thick outer part, which con-
tains the corpus striatum. The corpora striata are united by
an anterior commissure, which is not of large size. The thin-
ning of the inner wall of the lobes, from the margin of the
foramen of Munro backward, which gives rise to the fissure
of Bichat in the Mammalia, extends for a very short distance
in the Sauropsida, even in birds.

The olfactory lobes are usually elongated, and contain ventri-
cles continuous with those of the prosencephalic hemispheres.

In all Sauropsida the motor nerves of the tongue pass
through a foramen in the exoccipital bone. Hence, twelve
pairs of cranial nerves are present, except in the Ophidia,
which possess no spinal accessory nerve.

The lateral cutaneous branches so generally sent to the
trunk by the pneumogastric in the Lchthyopsida are absent,
but the pneumogastric gives a recurrent branch to the larynx,
The third, fourth, and sixth nerves arise quite independently
of the fifth.

260 THE ANATOMY OF VERTEBRATED ANIMALS.

The sympathetic is well developed, except in the Ophidia,
where it is not distinct from the spinal nerves, in the greater
part of the trunk.

Fig. 91—The brains of a Lizard (Psammosawrus Bengalensis) and of a bird (Meleagris
gallopavo), in longitudinal and vertical section. The upper figure represents the liz-
ard’s brain; the lower (taken, like Fig. 90, B, D, from Carus’s “ Erliuterungs-Tafeln “)
that of the bird.

The letters as in the preceding figure, except Z. t., lamina terminalis, or anterior wall
of the third ventricle; 7 Jf, foramen of Munro; a., anterior commissure; 7h. £., thala-
mencephalon; s., soft commissure; 7., posterior commissure; @v., indicates the exact point
of exit of the fourth pair from that part of the brain which answers to the value of Vieussens.

The Ophidia, many Sauria, and Aves, possess nasal glands,
which, in birds, attain a large size, and lie more usually upon
the frontal bone, or in the orbits, than in the nasal cavity.

The eye, rudimentary in some Ophidia and Lacertilia, is
usually large; and sometimes, as in many birds and in the ex-
tinct Lchthyosauria, attains very great absolute and relative
dimensions.

’
q
P

Se ee

a a eee

THE EYE-MUSCLES IN SAUROPSIDA. 261

In the Ophidia and some Lacertilia (the Amphisbeenoidea,
some Scincoidea, all Ascalobota), the integument is continued
over the eye, and becomes transparent. ‘These reptiles are
commonly said to possess no eyelids; but it must be remarked
that this is not true of them in the sense in which it is true of
most osseous fishes, as the transparent covering of the eye
really represents the two eyelids of the higher Vertebrata, and
is separated from the eyeball by a chamber lined by conjunc-
tiva, which communicates with the nose by a lachrymal canal,
In the other Sauropsida two lids are developed, and each
generally possesses a special palpebral muscle, which acts as
an elevator of the upper, and a depressor of the lower, lid. In
some Scincoidea the middle of the lower lid is transparent.
In many Lacertilia it contains a cartilage or an ossification.

Most lizards, all Chelonia, Crocodilia, and Aves, possess
w nictitating membrane moved by special muscles, which pre-
sent three different arrangements.

In the lizards a short thick muscle (dursalis) is attached to
the inner and posterior wall of the orbit, and ends in a fibrous
sheath. A tendon, one end of which is attached to the pre-
sphenoidal region of the inner wall of the orbit, passes back-
ward through the sheath, and then forward to be attached to
the nictitating membrane. When the muscle contracts it
necessarily pulls the latter over the eye. A Harderian gland
is always developed, and a lachrymal gland very generally,
though not always. .

In the Chelonia, muscular fibres (forming the so-called
pyramidalis muscle) arise from the inner side of the eyeball,
and, arching over it and the optic nerve, are inserted partly
into the outer edge of the nictitating membrane, partly into
the lower eyelid. The Crocodilia have a pyramidalis muscle
taking the same origin and course; but it sends no fibres to
the lower eyelid, its tendon being inserted altogether into the
nictitating membrane.

The third arrangement, which in a manner combines to-
gether the first and the second, is that seen in birds. A py-
ramidalis rouscle arising from the inner and under surface of
the eyeball, soon ends in a tendon which sweeps round the
upper and outer surfaces of the sclerotic to the nictitating
membrane, as in the crocodiles. But there is also a bursalis
muscle, which however arises, not, as in lizards, from the wall
of the orbit, but from the upper surface of the sclerotic itself,
whence it passes backward and ends in a fibrous sheath which
encloses the tendon of the pyramidalis, The contraction of

262 THE ANATOMY OF VERTEBRATED ANIMALS.

this muscle necessarily tends to draw the tendon of the py-
ramidalis away from the optic nerve. A tubercle is some-
times developed from the sclerotic above the entrance of the
optic nerve, and prevents the tendon of the pyramidalis from
shifting forward and inward.

The eyeball is always moved by four recti and two obliqui.
The superior oblique does not pass over a pulley. The Che-
lonia and most Lacertilia have a more or less completely de-
veloped retractor, or choanoid, muscle.

A ring formed of bony plates is developed in the fore-part
of the sclerotic in Lacertilia, Chelonia, Ichthyosauria, Di-
cynodontia, Pterosauria, and Aves, but not in Cphidia, Plesi-
osauria, or Crocodilia.

The iris and the tensor choroidet contain striated muscu-
lar fibres.

A pecten is very generally developed. It attains a large
size, and becomes much plaited, in most Aves.

Only Crocodilia and Aves possess a rudiment of an exter-
nal ear.

The Ophidia and the Amphisbeenoidea have no tympanic
cavity. In some Chelonia, in Sphenodon, and in the Chamz-
leons, the tympanic membrane is covered by the integument,
but a tympanic cavity exists. In Lacertilia, the tympanic
cavities communicate by wide openings with the pharynx;
but in Chelonia, Crocodilia, and Aves, the communicating
passages, reduced in size, become Eustachian tubes. In the
Chelonia, these curve backward, downward, and inward,
round the quadrate bones, and open separately on the roof of
the mouth. In the Crocodilia there are, as has been described
above (p. 219), three Eustachian tubes—one median and two
lateral. In Aves, there is but one Eustachian aperture, an-
swering to the median of the Crocodilia; and, as in the latter
group, each Hustachian tube usually traverses the osseous
base of the skull, to join with its fellow in the common aper-
Eure.

The stapes is a columelliform bene, the outer end of which
is attached to the tympanic membrane, where the latter is
developed; but lies among the muscles when there is no tym-
panic cavity.

All Sauropsida possess a fenestra rotunda, as well as a
JSenestra ovalis, and all have a cochlea, which is never coiled
spirally, and is more rudimentary in the Chelonia than in
other groups. Three semicircular canals, an anterior and

THE ALIMENTARY CANAL IN SAUROPSIDA. 263

posterior vertical, and an external horizontal, are connected
with the membranous vestibule. In Aves, the anterior vertical
canal is very large in proportion to the others, and the adja-
cent crura of the two vertical canals overlap before they unite
with one another.

Labial and buccal glands are developed in some Sauropsida,
and one of them, on each side, attains a large development in
the poison-glands of the venomous snakes. Well-developed
sublingual, submaxillary, and parotid glands appear in Birds,
and the sublingual glands attain an immense size in the Wood-
pecker. The tongue varies greatly, being sometimes obsolete,
as in the Crocodile and some birds (e. g., the Pelicans), some-
times horny and even spinose, sometimes fleshy. In the
snakes, and some lizards, the tongue is forked, and capable
of retraction into a basal sheath. In the» Chameleons, it is
clubbed at its extremity, and can be retracted or protruded by
the invagination or inversion of its hollow stem.

The alimentary canal of the Sauropsida is generally divided
into an cesophagus, a simple stomach, a small intestine and
large intestine, which last always terminates in a cloaca. It
is invested by a peritoneal coat, which generally follows all
the curvatures of the intestine. But in the Ophidia, the folds
of the small intestine are united by fibrous tissue, and enclosed
by a common sheath of peritonzeum.

The stomach is usually a simple dilatation of the alimen-
tary canal, the cardiac and pyloric apertures of which are
remote from one another; but, in the Crocodiles, and in most
Birds, the pyloric and cardiac apertures are approximated. In
many Crocodilia and Aves, there is a pyloric dilatation before
the commencement of the duodenum.

In the Crocodilia, and in Aves, the walls of the stomach
are very muscular, and the muscular fibres of each side radiate
from a central tendon or aponeurosis. The thickening of the
muscular tunic of the stomach attains its maximum in the
graminivorous birds; and it is accompanied by the develop-
ment of the epithelium into a dense and hard coat, adapted
for crushing the food of these animals. Birds commonly aid
the triturating power of this gastric mill by swallowing stones ;
but this habit is not confined to them, crocodiles having been
observed to do the same thing.

Birds are further remarkable for the development of a
broad zone of glands in the lower part of the cesophagus,
which is usually dilated, and forms a proventriculus, connected

264 THE ANATOMY OF VERTEBRATED ANIMALS.

by a narrow neck with the above-mentioned muscular stomach
or gizzard (gigerium).

Some Ophidia have a ceecum at the junction of the small
intestine with the large; and two such czeca, which sometimes
attain a large size, are very generally developed in Aves. In
this class also, the small intestine, not unfrequently, presents
a cecal appendage, the remains of the vitelline duct. The
duodenum of Birds constantly makes a loop, within which the
pancreas lies, as in Mammalia.

The liver in the Sauropsida almost always possesses a
gall-bladder, which is usually attached to the under surface
of the right lobe, but in the Ophidia is removed to some
distance from it.

A peculiar glandular sac, the Bursa Fabricii, opens into
the anterior and dorsal region of the cloaca in birds.

Three forms of heart are found in the Sauropsida. The
first is that observed in the Chelonia, Lacertilia, and Ophid-

ia ; the second, that in the Crocodilia ; and the third, that —

in Aves.

1. In the Chelonia, Lacertilia, and Ophidia, there are
two auricles. Generally, a distinct sinus venosus, with con-
tractile walls, and communicating by a valvular aperture with
the auricle, receives the blood from the venw cave, and pours
it into the right auricle. The pulmonary veins usually open
by a common trunk into the left auricle.

The interauricular septum is rarely (in some Chelonia)
perforated. Its ventricular edge spreads out on each side into
a broad membranous valve, the edge of which, during the
systole, flaps against a ridge, or fold, developed, on one, or
both sides, from the margin of the auriculo-ventricular aper-
ture, and constituting a rudiment of a second valve. The
ventricle contains only one cavity, but that cavity is im-
perfectly divided into two or three chambers, by septa devel-
oped from its muscular walls.

In the Turtle (Fig. 92), a partly muscular, and partly carti-
laginous, septum extends from the front wall of the ventricular
cavity toward its right-hand end. It imperfectly divides the
common ventricular cavity into a right small, and a left large,
moiety. The latter of these receives the blood from the auri-
cles. In consequence of the elongated form of the ventricular
cavity, and the projection into it of the large auriculo-ven-
tricular valves, especially of that of the right side, this left and
larger moiety of the common ventricle is virtually divided into

———

THE HEART IN SAUROPSIDA. 265

two, a left and a right, at the time of the auricular systole.
The left portion becomes filled with arterial blood from the
left auricle, and is distinguished as the cavum arteriosum ;
the right receives the venous blood from the right auricle, and
is the cavum venosum.

No arterial trunk arises from the cavwim arteriosum, but
two arterial trunks arise from the right-hand end of the cavum
yenosum , these are the two aortic arches. One of these
passes to the left and the other to the right side, and thev

"1a 92.—The Heart of a Turtle (Chelone midas).—A, a drawing from nature: the ventral
face of the ventricle being laid open. B, a diagram explanatory of the arrangement of
the cavities and vessels. R. A., ZL. A., right and left auricles. 2, x, arrows placed in
the auriculo-ventricular apertures to indicate the course of the blood at the auricular
systole. 4, the right, and v!, the left median auriculo-ventricular valves. (C. v., cavwm
venosum. C. p., cavum pulmonale. a, the incomplete septum which divides the
cayum pulmonale from the rest of the cavity of the ventricle. P.A., pulmonary artery.
&. Ao., L. Ao., right and left aorte. s, arrow showing the course of the blood in tha
left aorta; 7, in the right aorta; z,in the pulmonary artery; y, between the cavwm

cenosum and cavum pulmonale ; x, in the left, and w, in the right auriculo-ventriculat
aperture,
12

266 THE ANATOMY OF VERTEBRATED ANIMALS.

cross one another as they do so, because the origin of the left
arch lies more to the right than does the origin of the right
arch. The ostia of both arches are guarded by semi-lunar
valves; and that of the left arch is placed below and to the
right of that of the right arch. As no arterial trunk arises
from the cavum arteriosum, the red blood can be driven out
of the latter, during the systole, only into the cavum venosum.

The right, comparatively small, moiety of the ventricle
is separated from the cavum venosum by the already-men-
tioned septum, which is attached between the origin of the
left aortic arch and that of the pulmonary artery, its free edge
looking toward the dorsal face of the heart. Thus the pul-
monary artery arises from what is, virtually, a separate sub-
division of the ventricle, or a cavum pulmonale.

When the systole of the ventricle takes place, the practical
result of these arrangements is, that the pulmonary artery,
and the aortic arches, at first, receive wholly venous blood
from the cavum venosum and cavum pulmonale. But as the
arterial blood of the cavum arteriosum is driven into the
cavum venosum, the venous blood of the latter tends to be
excluded from the mouths of the aortic arches, and to be
driven into the cavum pulmonale, while the aortic arches
receive arterialized blood. ‘The left arch receives a larger pro-
portion of venous blood than the right. As the ventricle
contracts, the free edge of the muscular septum approaches
the dorsal wall of the ventricle, and gradually closes the access
to the cavum pulmonale, which thus finally expels the venous
blood which it received from the cavum venosum, but admits
none of the arterialized blood; consequently none of this
reaches the lungs.

2. In the Crocodilia, the cavum venosum and the cavum
arteriosum are converted into perfectly distinct right and left
ventricles. The right ventricle gives off the pulmonary artery,
and, in addition, an aortic arch which crosses over to the left
side. From the left ventricle only a single trunk arises, and
this, crossing to the right side, becomes the right aortic arch,
of which the dorsal aorta is the direct continuation. The walls
of the two aortic arches are in contact where they cross one
another ; and, at this point, a small aperture, situated above
the semilunar valves, places the cavities of the two arches in
communication.

Thus, in the Crocodilia, the venous and the arterial cur-
rents communicate only outside the heart, not within it, as in
the foregoing groups.

|
|
|

THE LARYNX IN SAUROPSIDA. 267

The septum of the cavum pulmonale remains as a small
muscular band, and the fold of the outer lip of each auriculo-
ventricular aperture has become a distinct membranous valve.

3. In Aves, the venous and arterial blood currents com-
municate only in the pulmonary and systemic capillaries. The
auricular and ventricular septa are complete, as in the Croco-
dilia ; but the right ventricle gives off only the pulmonary
artery, the left aortic arch having disappeared. The septum
of the cavum pulmonale becomes a great muscular fold, and
takes on the function of an auriculo-ventricular valve. At the
origin of the pulmonary artery, and at that of the aortic arch,
three semilunar valves are developed.

In Reptiles there are usually only two aortic arches, one
on each side, answering to the fourth pair of arches of the
embryo. The right gives off the carotid and_ subclavian
arteries, and passes directly into the trunk of the dorsal aorta.
The left commonly gives off visceral arteries, and becomes a
good deal diminished in size before joining the common trunk.

In many Lacertilia, four aortic arches (answering to the
third and fourth pairs of the embryo) persist, two anterior
arches, from which the carotids are given off, springing, by a
common trunk, from the right ordinary aortic arch.

In the Reptilia, most of the blood of the hind-limbs and
tail passes through one or other of two “portal systems”
before reaching the heart, the one portal system lying in the
kidney, the other in the liver. The portion which goes to the
liver is carried to it mainly by the anterior abdominal veins,
which are represented by two trunks in most Reptilia, by one
in the Ophidia.

In Aves there is no renal portal system, and the anterior
abdominal vein opens into the inferior vena cava close to the
heart. Nevertheless a median trunk, which is given off from
the caudal vein, carries a considerable proportion of its blood
directly into the hepatic portal system.

All the Sauropsida possess a larynx, a trachea, and one
or two lungs. The bronchi do not divide dichotomously, as
they do in Mammalia.

In Chelonia and Crocodilia the larynx consists of a cir-
cular cartilage apparently corresponding with both the thyroid
and the cricoid of the higher Vertebrata ; and of the arytenoid
cartilages, articulated with its anterior and dorsal edge.

The Lacertilia have, for the most part, a similar larynx,
but the circular cartilage is often interrupted by round, or

268 THE ANATOMY OF VERTEBRATED ANIMALS.

elongated, membranous fontanelles. In the Chameleons, the
mucous membrane of the larynx between the circular cartilage
and the first ring of the trachea protrudes in the form of an
air-sac.

In the Amphisboenoidea, and in the Ophidia, the skeleton
of the larynx consists of two lateral longitudinal bands of
cartilage, united by from four to sixteen transverse bands. In
other words, the structure which answers to the circular carti-
lage is greatly elongated, and has many transversely-elon-
gated fontanelles. ‘There is a single arytenoid cartilage,
which is sometimes represented by a process of the anterior
dorsal margin of the circular cartilage. An epiglottis is rarely
present.

In Birds there are distinct thyroid, cricoid, and arytenoid
cartilages, which may be more or less completely ossified.
Sometimes an epiglottis is added.

The voice of Birds, however, is not formed in the larynx,
but in the syrinz, or lower larynx, which may be developed
in three positions: 1. At the bottom of the trachea, from the
trachea alone. 2. At the junction of the trachea and bronchi,
and out of both. 3. In the bronchi alone. The syrinx may
be altogether absent, as in the Ratitew and the Cathurtida, or
American vultures.

The commonest form of syrinx is the second mentioned
above, or the broncho-tracheal syrinx. It is to be met with in
all our common song-birds, but is also completely developed in
many birds, such as the crows, which have no song. In its
commonest condition this form of syrinx presents the following
characters : The hindermost rings of the trachea coalesce, and
form a peculiarly-shaped chamber, the tympanum. Immedi-
ately beyond this, the bronchi diverge, and from their posterior
wall, where one bronchus passes into the other, a vertical fold
of the lining membrane rises, in the middle line, toward the
tympanum, and forms a vertical septwm between the anterior
apertures of the two bronchi. The anterior edge of this
septum is a free and thin membrana semilunaris, but in its
interior a cartilaginous or osseous frame is developed, and
becomes united with the tympanum. ‘The base of the frame
is broad, and sends out two cornua, one along the ventral, and
the other along the dorsal, edge of the inner wall of the bron-
chus of its side; which, in this part of its extent, is membra-
nous and elastic, and receives the name of the membrana tym:
paniformis interna.

The bronchial “rings” opposite this are necessarily ir

ee ee ee ed

THE RESPIRATORY ORGANS IN SAUROPSIDA. 269

complete internally, and have the form of arches embracing
the outer moiety of the bronchus. ‘The second and third of
these bronchial arcs are freely movable, and elastic tissue,
accumulated upon their inner surfaces, gives rise to a fold of
the mucous membrane, which forms the outer boundary of a
cleft, bounded, on the inner side, by the membrana semiluna-
ris, The air forced through these two clefts from the lungs
sets their elastic margins vibrating, and thus gives rise toa
musical note, the character of which is chiefly determined by
the tension of the elastic margins and the length of the tra-
cheal column of air. The muscles, by the contraction of which
these two factors of the voice are modified, are extrinsic and
intrinsic. The former are possessed by birds in general, and are
usually two pair, passing from the trachea to the furcula and to
the sternum. Some birds possessing a broncho-tracheal syrinx
suchas has been described, as the Alectromorphe, Chenomorphe
and Dysporomorphe, have no intrinsic muscles. Most others
have one pair, attached, one on each side, to the rings of the
trachea above, and to the tympanum, or the proximal bronchial
arcs, below. The majority of the Coracomorphe have five or
six pairs of intrinsic syringeal muscles, which pass from the
trachea and its tympanum to the movable bronchial arcs. The
Parrots have no septum, and only three pairs of intrinsic

muscles,

The tracheal syrinx occurs only in some American Cora-
comophee. The hinder end of the trachea is flattened, and
six or seven of its rings above the last are interrupted at the
sides, and held together by a longitudinal ligamentous band,
Thess rings are excessively delicate, so that this part of the
trachea is in great part membranous.

The bronchial syrinx occurs only in Steatornis, and Cro-
tophaga.

In the genus Cinyzxis, among the Chelonia, and in some
species of Crocodilus (C. acutus, e. g.), the trachea is bent
upon itself. Similar flexures attain an extraordinary develop-
ment in many birds, and may lie outside the thorax under the
integument (Zetrao urogallus, some species of Craxand Pe-
nelope) ; in the cavity of the thorax (some Spoonbills) ; on the
exterior of the sternum (some Swans and Cranes); or even
ina sort of cup formed by the median process of the furcula
(the Guinea-fowl). In the Emeu some of the rings of the
trachea are incomplete in front, and bound the aperture of an
air-sac which lies in front of the trachea. Some birds (Apte-
nodytes Procellaria) have the trachea divided by a longitu:

270 THE ANATOMY OF VERTEBRATED ANIMALS.

dinal septum, as in Sphargis among the Chelonia. The tras
cheal tympanum is greatly enlarged in Cephalopterus, and in
many Ducks, Geese, and Divers; and in these aquatic birds
the enlargement is more marked in the males, and is usually
asymmetrical, the left side being generally the larger.

In the Ophidia, the bronchus opens at once into the lung ;
and the latter is an elongated sac, the walls of which are pro-
duced into numerous septa, which render the cavity highly
cellular near the bronchus, while, at the opposite end, they
become smooth and but little vascular. In this latter region
the lung may receive its blood from the systemic and not
from the pulmonary circulation. The lungs are always un-
equal in size, and the left is usually the smaller. Very fre-
quently, especially among the poisonous snakes, one lung is
rudimentary or altogether absent; and the posterior portion
of the trachea may take on the structure of a lung.

The lungs of Lizards much resemble those of the Ophidia,
and they are elongated and unequal in size in the snake-like
Lacertilia, In the ordinary lizards they are more rounded
and the trachea and bronchi are shorter. In many Chame-
leons, and in some Geckos, the posterior half of each lung is
produced into narrow diverticula, which lie among the abdomi-
nal viscera, and foreshadow the air-sacs of birds.

In the Crocodilia each bronchus traverses its lung, and at
first retains, but soon loses, its cartilaginous rings. Lateral
apertures in the walls of the bronchus lead into sacculated
pouches, each of which resembles the lung of an ordinary La-
certilian.

The Chelonia have similar lungs; but while, in the fore-
going groups, the two lungs are free and invested on all sides
by the peritonzeum, in this they are fixed against the imner
periosteum of the carapace, and are covered by peritonzeum on
their ventral face only. This resemblance to the arrange-
ment of the lungs in birds is increased by the presence of a
muscular diaphragm, the fibres of which spread over the ven:
tral faces of the lungs.

In Aves the lungs are firmly fixed on each side of the ver-
tebral column, the dorsal surface of each lung being moulded
to the superjacent vertebre and ribs. The muscular fibres of
the diaphragm arise from the ribs outside the margins of the
lungs, and from the vertebral column, and end in an aponeu-
rosis upon the ventral surface of the lungs. :

Each bronchus enters its lung nearer the centre than the
anterior edge; and, immediately losing its cartilaginous or

THE AIR-SACS IN BIRDS. 271

bony rings, dilates, and then traverses the lung, gradually
narrowing, to the posterior edge of that viscus, where it ter-
minates by opening into the posterior air-sac, which generally
lies in the abdomen. From the inner side of the bronchus, ca-
nals are given off, one near its distal end, and others near its
entrance into the lung, which pass directly to the ventral sur-
face of the lung, and there open into other air-sacs. Of these
there are four. Two, the anterior and the posterior thoracic,
lie on the ventral face of the lung in the thorax. The other
two are situated in front of its anterior end, and are extra-
thoracic. The external and superior is the cervical, the inter-
nal and inferior, the interclavicular. ‘This last unites into one
cavity with its fellow of the opposite lung. Thus there are
altogether nine air-sacs; two posterior or abdominal, four
thoracic, two cervical, and one interclavicular. Other large
canals given off from the bronchus do not end in air-sacs, but
those which pass from the inner side of the bronchus run
along the ventral surface, and those on the outer side, along
the dorsal surface, of the lung. Here they give off, at right
angles, series of secondary canals, and these similarly emit
still smaller tertiary canals ; and thus the whole substance of
the lung becomes interpenetrated by tubuli, the walls of the
finest of which are minutely sacculated. The different sys-
tems of tubuli are placed in communication by perforations in
their walls.

in most birds, the air-sacs (except the anterior and pos-
terior thoracic, which never communicate with any cavity but
that of the lungs) are in connection with a more or less exten-
sively ramified system of air-passages, which may extend
through a great many of the bones, and even give off subcu-
taneous sacs. Thus the interclavicular air-sac generally sends
a prolongation into each axilla, which opens into the proximal
end of the humerus, and causes the cavity of that bone to be
full of air. When the sternum, the ribs, and the bones of the
pectoral girdle, are pneumatic, they also receive their air from
the interclavicular air-sacs. The cervical air-sacs may send
prolongations along the vertebral canal of each side, which
supply the bodies of the cervical vertebre, and communicate
with elongated air-chambers in the spinal canal itself. When
the dorsal vertebrae are pneumatic, they communicate with
the system of the cervical air-sacs. The abdominal air-sacs
send prolongations above the kidneys to the sacral vertebree
and to the femora, whence these bones, when they are pneu-
matic, receive their air

272 THE ANATOMY OF VERTEBRATED ANIMALS.

The pulmonary air-sacs and their prolongations do not
communicate with the air-cavities of the skull, which receive
their air from the tympana and the nasal chambers. In some
birds, the air is conducted from the tympanum to the articular
piece of the mandible by a special bony tube, the siphonium.

In all Sauropsida, the ureters open directly into the cloaca,
which is provided with a urinary bladder in the Lacertilia
and the Chelonia, but not in other feptilia, nor in Aves.

Organs of copulation present themselves under three
forms :

1. In the Chelonia, the Crocodilia, and the Ostrich, a sim-
ple solid penis, grooved upon its posterior aspect, is attached
to the anterior wall of the cloaca, and contains erectile tissue.
In the ostrich this penis lies in a sac of the cloaca, into which
it can be retracted somewhat as in the Menotremata.

2. In many birds, such as the Rheide, Casuaride, Aptery-
gide, Tinamomorphe ; Penelope, and Crax, among the Alec-
toromorphe ; and in many aquatic birds, there is also a single
penis attached to the front wall of the cloaca, grooved on its
dorsal side, and supported by two fibrous bodies coated with
more or less erectile tissue. But the distal end of the penis
is invaginated, and the involution held in this position, except
during erection, by an elastic ligament.

3. In Lacertilia and Ophidia, two copulatory organs are
developed at the sides of the cloaca. The integument is pro-
longed inward, on each side, into a blind sac, which lies upon
the inferior caudal muscles. The inner surface is often armed
with spiny developments of the epidermis, and presents a
groove, which is continued on the parietes of the cloaca to the
aperture of the vas deferens. The wall of the blind sac con-
tains erectile tissue, and it can be erected or retracted by ap-
propriate muscles.

CHAPTER VIL
THE CLASSIFICATION AND ORGANIZATION OF THE MAMMALIA,

Tue class Mammalia is divisible into the following groups:

A. There are large and distinct coracoid bones, which articulate with the
sternum.

The ureters and the genital ducts open into a cloaca, into which
the urinary bladder has a separate opening.

The penis is traversed by a urethral canal which opens into the
cloaca posteriorly, and is not continuous with the cystic urethra.

There is no vagina.

The mammary glands have no teats.

J.—ORNITHODELPHIA.
1. Monotremata.

B. The coracoid bones are mere processes of the scapula in the adult, and
do not articulate with the sternum. &t
The ureters open into the bladder; the genital ducts, into a ure-
thra or vagina.
The cystic urethra is continuous with the urethral canal of the penis
There is a single or a double vagina.
The mammary glands have teats.
— A, The embryo does not become connected with the wall of the
uterus by an allantoic placenta. The vagina is double.

II].—DIpELrPuta.
2. Marsupialia.
- 4. The embryo has an allantoic placenta. The vagina is single.
TII.—Monopetpaia.*
a. Median incisor teeth are never developed in either jaw.

8. EHdentata.

b. Median incisor teeth are almost always developed in one or
both jaws.

* The manner in which the Monodelphia are here subdivided must be re-
garded as merely provisional.

274 THE ANATOMY OF VERTEBRATED ANIMALS.

i. The uterus develops no decidua (Won-deciduata).
4. Ungulata.
5. Toxodontia (?).* é
6. Sirenia (?).*
7. Cetacea.
ti. The uterus develops a decidua (Deciduata).
a. The placenta is zonary.
8. Hyracoidea.
9. Proboscidea,
10. Carnivora.

B. The placenta is discoidal.
11. Rodentia.
12. Insectivora.
13. Cheiroptera.
14. Primates.

I, The Orn1rHODELPHIA are those Mammals which approach
nearer to the Sauropsida, although separated from them by all
the essential characters of the Mammalia which have already
been defined.

The two genera Echidna and Ornithorhynchus, which con-
stitute this division, agree with one another, and differ from
all other Mammals, in the combination of the following char-
acters :

In the spinal column, the centra of the vertebree are devoid
of epiphyses. The os odontoideum, or so-called “ odontoid
process ” of the second cervical vertebra remains for a lon
time, if not throughout life, unanchylosed with the body of
that vertebra, as is the case in many Reptiles. And some of
the cervical ribs, in like manner, long persist in a separate
condition.

A striking Sauropsidan and Amphibian feature, peculiar to
the Ornithodelphia, is seen in the fact that the coracoid,
which is a large bone, articulates with the sternum directly.
In front of it is another considerable ossification called the
epicoracoid, which corresponds in position, though not in the
manner of its ossification, with the ossified cartilage so termed
in Reptiles. In these Mammals alone, again, there is a T-shaped
interclavicle, which supports the clavicles. The central por-
tion of the acetabulum remains unossified, and hence, in the
dry skeleton, appears perforated, as in Aves, Ornithoscelida,
and Crocodilia.

The inner tendons of the external oblique muscles are ossi-
fied for a considerable distance; and these ossifications appear
in the dry skeleton as bones, which are articulated with the

* The placentaticn of the Zoxodontia and Stirenia is unknown.

i eR — hel © Bn gt te «

THE ORNITHODELPHIA. 275

inner portions of the anterior margins of each pubis. These
bones correspond with those which exist in a like position in
the Didelphia, and are called marsupial bones; though the
term is peculiarly inappropriate, inasmuch as they have noth-
ing to do with the marsupium, or pouch, in which the young
are sheltered in most of the Didelphia.

In the upper view of the brain the cerebellum is left com-
pletely uncovered by the cerebral hemispheres. ‘The latter
are connected by only a very small corpus callosum. The an-
terior commissure, unlike that of any of the Sauropsida, at-
tains a very great size,and the hippocampal sulcus is pro-
longed forward to the corpus callosum.

In the internal ear, the cochlea is only slightly bent upon
itself, not coiled into a spiral, as in other Mammalia. The
stapes is imperforate and columelliform, and the malleus is very
large, while the incus is singularly small.

There is a spacious cloaca common to the rectum, genital
and urinary organs, as in the Sauropsida and many Lchthy-
opsida. In both sexes a long urogenital canal opens into the
front part of the cloaca. At its anterior end there are five
distinct apertures—one in the middle line for the bladder, and
two on each side, which are the openings of the genital ducts
and of the ureters. Thus in these Mammalia, and in these
only, the ureters do not open into the urinary bladder. The
testes remain in the abdomen throughout life. The penis is
attached to the front wall of the cloaca, and is not united
directly with the ischia. It is traversed by a urethral canal,
which opens into the cloaca posteriorly, but is not directly con-
nected with either the seminal or the urinary passages. It is
probable that, during copulation, the posterior aperture of the
penial urethra is applied to the anterior aperture of the uro-
genital canal, so as to form a continuous passage for the semen.

The ova of the female are very large and project from the
surface of the ovary, as in the Sauropsida. The mouths of
the Fallopian tubes are not fimbriated. 'There is no vagina
distinct from the urogenital chamber. The mammary glands
are situated, one upon each side of the middle line, in the
_ hinder part of the abdominal wall. The various ducts of the
gland open upon a small area of the integument which is not
raised up into a teat, so that, in the strict etymological sense
of the word, these animals are not Mammalia. The mam-
mary gland is compressed by the panniculus carnosus, and not
by any prolongation of the cremaster.

There is no sufficient evidence of the nature of the feetai

276 THE ANATOMY OF VERTEBRATED ANIMALS.
appendages; but the embryo is born in an imperfect condition,
and may be provided with a knob or caruncle upon the pre-
maxille, such as is found in the Sauropsida. In the adult
the heart exhibits a fossa ovalis.

Both genera of the Ornithodelphia are restricted to Aus-
tralia, including Tasmania under that name.

The one of them, Hchidna, has the body covered with
spines, like a porcupine. It possesses strong digging feet,
and a narrow, toothless mouth, from which the long tongue,
with which it licks up the ants upon which it preys, is pro-
truded.

The other genus, Ornithorhynchus, has soft fur ; a flattened
muzzle resembling the beak of a duck, and covered witha
leathery integument; and clawed, but strongly webbed feet,
fitting it for its altogether aquatic mode of life. The Orni-
thorhynchus, in fact, frequents fresh-water pools and rivers,
very much like a water-rat, sleeping and breeding in burrows
excavated in the bank.

In these animals the angle of the mandible is not inflected.
They are devoid of any external ear; and,in the males, a kind
of spur, which is perforated, and gives exit to the secretion of
a gland, is attached to the astragalus. The function of this
organ is unknown. In each genus the heart is provided with
two superior cave. In “echidna the right auriculo-ventricle
valve is membranous, but, in Ornithorhynchus, it is more or
less fleshy.

The hemispheres of the brain are abundantly convoluted
in Echidna, but are smooth in Ornithorhynchus. The ovaries
are of equal size in Hchidna; but, in Ornithorhynchus, the
right is much smaller than the left, as in Birds. As has al-
ready been stated, chidna is entirely devoid of teeth, while
Ornithorhynchus has four large horny teeth.

Il. The Diwetput1a.—In the Didelphia, the “ odontoid
process ” early becomes completely anchylosed with the body
of the second vertebra; and, usually, all the cervical ribs
speedily lose their distinctness, as in Mammals in general.

The coracoid is reduced to a mere process of the scapula
and does not come near the sternum. There is no epicora-
coid, such as exists in the Ornithodelphia. There is no T-
shaped interclavicle, but the clavicles, which are always pres-
ent (except in Perameles) articulate with the manubrium of
the sternum, in the same way as in ordinary Mammalia.
The floors of the acetabula are completely ossified, and conse-

Nc ge =

THE DIDELPHIA. 274

quenuly are imperforate in the dry skeleton. The cochlea is
coiled upon itself.

There is a shallow cloaca, the sphincter muscle being com-
mon to the urinary and genital apertures, but there is no such
urogenital chamber as in the Monotremata. The ureters open
directly into the bladder.

In the male, the urogenital part of the urethra, and that
which traverses the penis, form one continuous canal, which
opens outward only at the extremity of the penis.

In the female, the vaginal is perfectly distinct from the
urinary passage. The mouths of the Fallopian tubes are fim-
briated, and the ova are not larger than those of the MWono-
delphia.

The mammary glands are provided with long teats.

In all the preceding characters the Didelphia agree with
the Monodelphia, and differ from the Ornithodelphia.

But they agree with the Ornithodelphia, and differ from
the Monodelphia in possessing either bones or cartilages, at-
tached to the pubes, in the position of the so-called marsupial
bones of the Ornithodelphia.

Again, the brain, the cerebral hemispheres of which may
or may not have a convoluted surface, is provided with a very
small corpus callosum, and a large anterior commissure. The
hippocampal sulcus is prolonged forward over the corpus cal-
losum.

The crura of the corpus cavernosum of the penis are not
fixed to the ischium.

The embryo does not become connected with the parent
by villi developed from the allantois, and it is born in a very
imperfect condition.

Certain characters are peculiar to the Didelphia. Thus,
the testes of the male pass into a scrotum, which is suspended
in front of the penis. In the female, the cremaster muscle is
largely developed, and spreads over the surface of the mam-
mary gland, which it compresses, so as to drive the milk out
of the projecting teat. There is no fossa ovalis on the right
side of the septum of the auricles. Very generally, though
not invariably, the Didelphia possess what is termed a marsu-
pial pouch, which is a sort of bag, formed by a fold of the in-
tegument of the abdomen, into which muscular fibres of the
»anniculus carnosus extend. These support the ventral wall
of the pouch, and are capable of closing its mouth, which may
be directed either forward or backward. The mammary glands

ie in the dorsal wall of this pouch, into which the teats project.

278 THE ANATOMY OF VERTEBRATED ANIMALS.

There is no direct communication between the female gen-
erative organs and the pouch; but the minute young are
transported, in the blind and imperfect state in which they
are born, into the interior of the marsupium, and each be-
comes attached to a nipple, which exactly fills its mouth. To
this it remains attached for a considerable period, the milk
being forced down its throat by the contraction of the cre-
master muscle. The danger of suffocation is averted by the
elongated and conical form of the upper extremity of the
larynx, which is embraced by the soft palate, as in the Ce-
tacea; and thus respiration goes on freely, while the milk
passes, on each side of the laryngeal cone, into the cesophagus,

It very commonly happens among the Didelphia that the
two long yvaginz are bent upon themselves, their proximal
ends becoming applied together and dilated, and these dilated
portions not unfrequently communicate. Another very gen-
eral peculiarity of the Didelphia is the inflection of the lower
margin of the angle of the mandible inward intoa strong hori-
zontal process. In the genus Zarsipes, however, this process
is absent.

There are further anatomical characters which are well
worthy of notice, though they are not so important as the
foregoing. |

The integument is always furry, never spiny or scaly, nor
provided with dermal scutes. The pinna of the external ear
is well developed. In the skull the carotid arteries pierce the
basisphenoid to enter the cranial cavity. The tympanic cavity
is in front, bounded by the alisphenoid; and, very generally,
the jugal furnishes part of the articular surface for the man-
dible.

Many of the cranial sutures, especially in the occipital
region, persist throughout life; and the squamosal, the united
periotic ossifications, and the tympanic bones remain distinct
from one another.

The jaws are always provided with true teeth; and, usual-
ly, these teeth are readily distinguished into incisors, canines,
false molars, and true molars. The canines, however, are ab.
sent in some genera, either in both jaws or in the mandible.
There are usually four true molar teeth, and, as Prof, Flower
has recently discovered, only one grinder succeeds another
vertically. It represents the last premolar. The molars never
possess a complex structure.

No didelphous mammal has three incisor teeth upon each
side above and below; and none but Phascolomys has an

°

THE DIDELPHLIA. 279

equal number of incisors in each jaw, the number of the
upper being usually in excess of that of the lower jaw.

The number of the dorso-lumbar vertebre is almost always
nineteen; and, of these, six are usually dorsal. The atlas is
generally incompletely ossified in the ventral median line.
The manus usually possesses five digits, but in Perameles and
Cheropus the outer digits become rudimentary.

The fibula is always complete at its distal end. In some
cases it becomes anchylosed with the tibia, while in the
Wombat (Phascolomys), the Phalangers (Phalangistide),
and the Opossums (Didelphic), it is not only free, but is ca-
pable of a rotatory movement upon the tibia, similar to the
movement of pronation and supination of the radius upon the
ulna in Man. The rotation of the fibula toward the ventral
side of the tibia is effected by a muscle which, in great meas-
ure, occupies the place of the interosseous ligament, and is
analogous to the pronator quadratus in the fore-limb. This
muscle is antagonized by the extensors of the digits, so far as
they arise from the fibula.

The digits of the pes vary remarkably in their form and
relative development among the MWarsupialia,; the different
subdivisions of the order being very well distinguished by the
modifications of the hind-foot.

Thus in the especially carnivorous Marsupials—the Didel-
phide, of America, and the Dasyuride, of the Australian
province—the second and third digits of the pes are not
united together by the integument. In the Didelphide, the
hallux is nailless, but large and opposable, so as to convert
the pes into a prehensile organ like that of many Primates,
in the Dasyuride, on the other hand, the hallux is rudimen-
tary or absent. In all the other marsupials, the second and
third digits of the pes are syndactyle, or united together by in-
tegument. In the Wombat, the fourth toe is bound together
with the other two, and the small hallux is devoid of a nail.
In the Phalangers, only the second and third toes are syn-
dactyle, and they are slender, compared with the other digits,
while the hallux is well developed and opposable. In the
Peramelide (Bandicoots) and Macropodide (Kangaroos), the
metatarsus is much elongated, and the second and third digits
united and slender, while the fourth toe is very large. The
hallux is reduced to its metatarsal bone in the Peramelida,
and the fifth digit is small or rudimentary. In the Kangaroos,
the hallux disappears altogether, but the fifth digit remains
well developed, though not so large as the fourth,

280 THE ANATOMY OF VERTEBRATED ANIMALS.

There is a great range of variation in the characters of the
brain. The carnivorous Marsupials (Didelphys, Dasyurus,
Thylacinus) exhibit the lowest type of cerebral structure, the
olfactory lobes being very large and completely exposed,
while the cerebral hemispheres are comparatively small and
quite smooth. In the Kangaroos, on the other hand, the
cerebral hemispheres present numerous convolutions and are
much larger in proportion to the olfactory lobes, which they
cover.

The stomach may be simple, as in most Marsupialia, or
provided with a cardiac gland (Phascolarctos, Phascolomys).
In the Kangaroos, it becomes immensely elongated, with
longitudinal muscular bands and transverse sacculations, so that
it resembles the human colon. The czecum, which is large in
the Kangaroos, but absent in the Dasyuride, is provided, in
the Wombat, with a vermiform appendix like that of Man.

The liver always possesses a gall-bladder. There are two
ven cave superiores, and they receive the venew azygos of
their respective sides. The tricuspid valve in the heart is
membranous. There is no inferior mesenteric artery, and the
external and internal iliacs arise separately from the aorta.

There are no vesiculz seminales, and the glans penis is
bifurcated in many species. ‘The marsupial pouch is absent in
some Opossums and Dasyuride. When it is present, its
mouth is usually directed forward, but in 7hylacinus and in
some Peramelide it looks backward. In Thylacinus also the
“marsupial bones” remain cartilaginous. The condition of
the foetus is known only in the Kangaroos, and further observa-
tions on the embryology of the Didelphia are much needed.
The foetus is said to possess a large umbilical sac, the vessels
of which extend on to the plaited chorion; and a small allan-
tois ; and to be devoid of a thymus gland.

The Didelphia are at present confined to the Australian
and the Austro-Columbian provinces, some few species stretch-
ing beyond the borders of the latter into the northern parts of
North America. The Didelphide alone are found in Austro-
Columbia, all the other groups being Australian.

Gigantic, Kangaroo-like, or Phalangistic, forms (Votothe-
rium, Diprotodon, Thylacoleo), have been found in post-ter-
tiary deposits and caves in Australia. In Europe, Didelphida
occur in Eocene strata; Didelphide, Dasyuride, and Macro-
podide (Phascolotherium, Amphitherium, Plagiaulax), in
middle Mesozoic rocks ; and Macropodide (?) (Microlestes) in
the Trias.

THE MONODELPHIA. 281

Ill. The Monopre.tput1a.—In the Monodelphia, the os
odontoideum very soon becomes anchylosed with the second
cervical vertebra, of which it appears merely as the odontoid
process 3 and the cervical ribs early become inseparably united
with their vertebree. The coracoid is reduced to a mere pro-
cess of the scapula, and there is no epicoracoid similar to that
of the Ornithodelphia.

Clavicles may be present or absent. When completely
developed they articulate directly, or by the intermediation of
more or less modified remains of the sternal end of the cora-
coid, with the sternum, and not with any interclavicle. The
acetabula are imperforate. The pelvis is devoid of marsupial
bones ; though, insome Carnivora, there are small cartilages
in the inner tendons of the external oblique muscle, which
have a corresponding form and relations.

The anterior commissure and the corpus callosum, no less
than the cerebral hemispheres themselves, vary greatly, the
brains of some “dentata very closely approaching those of the
Didelphiain respect of the corpus callosum and anterior com-
missure; while, as regards the hemispheres themselves, they
may either be so small as to allow the cerebellum to be com-
pletely exposed on the dorsal aspect, or so large as com-
pletely to cover it and project beyond it. The external sur-
face of the nemispheres, again, may be either perfectly smooth
or extremely convoluted.

The cochlea is coiled spirally. The reproductive and
urinary apertures, asa general rule, open quite separately from
the rectum. The ureters always open into the bladder. The
testes may remain in the abdomen throughout life, or may
pass into a scrotal pouch. But, when this scrotum forms a
distinct sac, it lies at the sides of, or behind, the penis, and
not in front of it. The cystic urethra is always continuous
with that part of the urethra which traverses the penis.

The ova are small, and the mouths of the Fallopian tubes
are fimbriated. ‘The vagina is a single tube, which may, how-
ever, be partially divided by a longitudinal partition. The
cremaster has no relation to the mammary glands, which are
provided with distinct teats.

The allantois is always well developed, and gives rise to
a placenta; and the young are born of large size, and active.

The great. majority of the Monodelphia, as thus defined,
are divisible according to the characters of their placenta into
non-deciduata and deciduata.

In the non-deciduata the foetal villi of the placenta are, at

282 THE ANATOMY OF VERTEBRATED ANIMALS.

birth, simply withdrawn from the uterine fossz, into which
they are received, and no part of the maternal substance is
thrown off in the form of decidua, or maternal part of the pla-
centa. In the deciduata, on the other hand, the superficial
layer of the mucous membrane of the uterus undergoes a
special modification, and unites, to a greater or less extent,
with the villi developed from the chorion of the foetus; and, at
birth, this decidual and maternal part of the placenta is thrown
off along with the foetus, the mucous membrane of the uterus
of the parent being regenerated during, and after, each preg-
nancy.

There are, however, two orders of existing monodelphous
Mammalia, the nature of the placentation of which is not yet
fully made out. One of these is the Strenia, the placentation
of which is unknown. The other is the ill-defined and hetero-
geneous assemblage called Adentata. Some of the members
of this group certainly possess deciduate placentz, while, in
others, it appears questionable whether the decidua is, or is
not, developed. And, as this group, the Hdentata, is decidedly
the lowest of the whole division, I shall take it first in order,
while the Sirenia are arranged, provisionally, among the Von-
deciduata.

The Eprntata, or Brura.—In these Mammals the teeth
are by no means always wanting, as the name of the group
would seem to imply; but, when teeth are present, incisors
are either altogether absent, or, at any rate, the median in-
cisors are wanting in both jaws. The teeth are always devoid
of enamel, consisting merely of dentine and cement. As they
grow for an indefinite period, they never form roots; and, so
far as our knowledge at present extends, those which first
appear are displaced | by a second set only in some of the Arma-
dillos. The ungual phalanges of the digits support long and
strong claws.

There are mammz upon the thorax, and sometimes, in ad-
dition, on the integument of the abdomen; or, in the inguinal
region,

The brain varies greatly, its hemispheres being sometimes
quite smooth, with a very small corpus callosum and large an-
terior commissure; while, in other cases, the corpus callosum
is much larger, and conyolutions appear upon the surface of
the brain.

The Hdentata are divided into the Phytophaga, or vege
table-feeders, and the Hntomophaga, or insect-eating forms.

THE EDENTATA PHYTOPHAGA. 288

Leaves are the chief food of the former group, while the latter
delight chiefly in ants, though some take, in addition, worms
and carrion.

1. In the Phytophaga the long bones are without medul-
lary cavities. The lateral part of the zygomatic arch sends
down a remarkable vertical process. The acromial process of
the scapula coalesces with the coracoid. In the carpus, the
scaphoid and the trapezial bones anchylose and form one. The
ischia become united with the anterior caudal vertebrae, and
these anchylose with the proper sacrals to form the long sacrum.

The ankle-joint has the character of a peg and socket, and
the hind-foot is, more or less completely twisted, resting upon
its outer edge, and not upon its sole.

Vascular canals connected with the pulp-cavity traverse
the dentine of the teeth.

The Phytophaga are divisible into two groups, one exist-
ing, and the other extinct. The former consists of the Sloths,
or Zardigrada ; remarkable animals, which are confined to
the great forests of South America, where they lead a purely
arboreal life, suspended by their strong, hooklike, claws to the
branches of the trees.

Their distinctive characters are these: The tail is short,
and the limbs exceedingly long and slender, the anterior be-
ing longer than the posterior pair. In both the fore-and the
hind-limbs the internal and the external digits are rudimen-
tary, but the hind-foot always has the three middle toes com-
pletely developed; while, in the fore-foot, it sometimes hap-
pens that only two remain. The ungual phalanges are very
long and hooked. |

The zygomatic arch is incomplete posteriorly, not being
united by bone with the squamosal. The cervical vertebrze
in this remarkable group sometimes exceed, and sometimes
fall short of, the number (seven) which is so characteristic of
the Mammalia in general; some species of Sloths having
nine, and others only six, vertebrz in the neck.

The pelvis is exceedingly spacious, and the acetabula are
directed backward as well as outward. The femur is devoid
of a ligamentum teres. The distal end of the fibula sends in-
ward a process which fits into a fossa situated upon the outer
surface of the astragalus, giving rise to that kind of peg-and-
socket ankle-joint which is peculiar to these animals.

A good deal of confusion prevails respecting the structure
of the ankle-joint in the Sloths. Cuvier (“ Ossemens fossiles,”
t. vili., p. 143) writes of the Ai, or three-toed Sloth:

284 THE ANATOMY OF VERTEBRATED ANIMALS.

“In the greater number of animals, the principal articu-
lation of the astragalus connects it with the tibia, by means
of a more or less loose ginglymus, which allows the foot to be
bent on the leg. But here the principal and superior facet of
the astragalus is a conical fossa, into which the pointed ex-
tremity of the fibula penetrates, like a pivot. (See Pl. 208,
Fig. 2a.) The inner edge of this fossa turns against a very
small facet, which occupies only a third of the lower head of
the tibia. The result of this arrangement is that the foot
turns on the leg, like a weathercock on its support, but that it
cannot be flexed. It further follows that the plane of the sole
of the foot * is almost vertical when the leg is so, and that the
animal can only place the plantar surface of its foot on the
ground by spreading out the leg so as to make it almost hori-
zontal.”

Meckle + has already justly remonstrated against Cuvier’s
assertion that only abduction and adduction are possible to
the pes of the Ai, affirming that it is capable of flexion and
extension, though only to a limited extent. A. Wagner fol-
lows Meckel, but Rapp (“ Edentaten,” p. 46) adopts Cuvier’s
statement in its fulness: “ Extension and flexion of the foot
cannot take place, but only abduction and adduction.” How-
ever, it is easy to demonstrate on the uninjured dead animal,
or, still better, on the limb from which the muscles have been
removed, while the ligaments have been left intact, that the
pes of the three-toed Sloth is capable of extensive motion in
three directions: first, in abduction and adduction; a move-
ment inazimuth, when the leg is vertical; secondly, in flexion
and extension; a more extensive movement in altitude, un
der the same circumstances; and, thirdly, in rotation upon its
own axis, by means of which the sole can be moved through
90° from a position perpendicular to the axis of the leg to one
parallel with it.

The anatomical arrangements upon which the execution
of these movements depend are the following: The astraga-
lus presents two facets to the bones of the leg, one of which
(when the pes is in the position usual in other quadrupeds)
looks inward and upward, while the other looks outward and
upward, The former, convex from before backward, as well
as from side to side, is by no means a mere rim, though it 1s

* Cuvier’s words are: ‘*I] en résulte encore que le plan, le corps du pied,
est presque vertical quand Ja jambe i'est.”’ i

Peay stein der vergleichenden Anatomie,’ 2te Theil., 2te Abtheilung
p. 457.

THE ANKLE-JOINT OF THE SLOTHS. 285

not so wide as the other. It is the proper proximal surface
of the astragalus, and articulates with the tibia. The other
surface is excavated by a deep conical pit. Into this is re-
ceived a correspondingly conical process of the distal end of
the fibula, which is directed from above and without, down-
ward and inward—not vertically, therefore, but very oblique-
ly. Hence, even if the pivot fitted its socket quite accurately,
there would still be abundant opportunity for flexion and ex-
tension, though the movement of the pes would be obliquely
inward, as well as upward, in the former case; and obliquely
outward, as well as downward, in the latter. But the socket
fits the pivot loosely, and hence, as experiment demonstrates,
the movement of the pes in flexion and extension is but very
slightly oblique.

The true movement of abduction and adduction is so much
less extensive than the movement in flexion and extension,
because it is checked by the short and strong internal and ex-
ternal lateral ligaments of the ankle-joint.

With respect to the rotation of the foot on its own axis—
it is to be observed, in the first place, that the calcaneum, cu-
boides, naviculare, the three cuneiformia, the three complete
and the three rudimentary metatarsals, and the three basal
phalanges of digits 77., 7i7., and 7v., are anchylosed together
into one bony mass; while, as in the manus, there is hardly
any motion between the basal and the middle phalanges.
Practically, in fact, the only bones of the pes which are moy-
able upon one another are: 1. The distal phalanges, which
have a movement of extension and flexion through 180° upon
the middle phalanges. 2. The tarso-phalangeal synostosis
above described is freely movable on the astragalus ; and the
joint is disposed in such a manner as to allow the sole of the
foot to be rotated from the plantigrade position in which it is
perpendicular to the axis of the leg, to the scansorial position,
in which it. lies parallel with the axis of the leg. It may be
doubted, however, whether the former position can be given
to the sole by the living animal. The ébc¢alis anticus and the
extensor hallucis longus are extremely strong muscles, and
have no efficient antagonists; so that their tonic contraction
must pull the navicular metatarsal tuberosity, into which they
are inserted, as far upward as it will go, causing the tarso-pha-
langeal synostosis to rotate upon the astragalus, and thus

obliging the sole of the foot to look inward.
’ In the two-toed Sloth, or Unau (Cholcpus), the general
structure of the ankle-joint is the same, but the fossa of the

286 THE ANATOMY OF VERTEBRATED ANIMALS.

astragalus looks almost directly outward, and the pivot of the
fibula is more nearly horizontal, when the leg is vertical. The
tibial facet of the astragalus locks directly upward. Hence,
the movement of the pes is more exclusively one of flexion
and extension than in the Ai. No anchylosis of the tarsal,
metatarsal, and phalangeal bones occurs, but the rotation of
the distal moiety of the tarsus upon the astragalus is much
more complete and permanent than in the Ai. The calcane-
um is twisted round under the astragalus, in such a manner
that its proper external face becomes inferior, while the articu-
lar surface for the cuboid is not only below, but is partially
internal to, the navicular facet of the astragalus. As a result
of this position of the cuboid, the outer metatarsals, which it
supports, are placed directly beneath the inner ones, and the
pes rests absolutely upon its outer edge, the plane of the sole
being vertical.

The Sloths, it thus appears, are naturally club-footed; but
neither in the Ai, nor in the Unau, does this depend in any
way on the structure of the ankle-joint. On the contrary, it
results, in the Unau, from the manner in which the calcaneum
and naviculare articulate with the astragalus; and, in the Ai,
from the action of the muscles on the tarso-phalangeal synos-
tosis. Neither in the Ai, nor the Unau, is there any thing to
interfere with free flexion and extension of the pes.

The teeth are five in number on each side above, and four
below, and become sharpened by mutual attrition into a chisel-
like form. The stomach is remarkably complex.

The Gravigrada are, for the most part, like the Sloths,
South American forms, but they are entirely extinct; and
while, in most respects, they resemble the Sloths, in others
they present an approximation to Ant-eaters.

The jugal arch may be complete or incomplete. The artic-
ular surfaces of the dorsal vertebrze are sometimes complicated
in a manner similar to that observed in the Ant-eaters. The
tail is very long and strong. The limbs are sliort and sub-
equal, while the fore-foot has the ulnar digit imperfect, as in
the Ant-eaters. The fibula has no inward process, and the
astragalus is consequently devoid of any fossa upon its outer
surface. But another kind of peg-and-socket ankle-joint is
produced by the interlocking of the surfaces of the tibia and
of the astragalus.

The great extinct animals, Megatherium, Mylodon, Mega-
lonyx, etc., the remains of which have been found almost wholly
in later tertiary deposits of America, belong to this group.

THE EDENTATA ENTOMOPHAGA. 287

2. The Entomophaga.—In this group of “dentata the
zygoma sends down no process from its lateral region, al-
though, in some rare cases, the anterior part of the arch has a
descending prolongation, The acromion and the coracoid do
not become united. The scaphoid and the trapezium remain
distinct; and the sole of the hind-foot rests upon the ground
by a greater or lesser extent of its whole surface, and not
merely by its outer edge.

The insectivorous Hdentates are divisible into four groups
—a. the Mutica, b. the Squamata, c. the Lubulidentata, and
d. the Loricata.

a. The group of the Mutica contains the genera Myrme-
cophaga and Cyclothurus, the Ant-eaters of South America.
The bodies of these animals are covered with hair, and they
are provided with very long tails, which are sometimes pre-
hensile. The skull is greatly elongated, and the small pre-
maxillz are but loosely connected with it. The jugal arch
is incomplete. In Myrmecophaga, the pterygoids, which are
very long, stretch back to behind the level of the tympanic
bullze, with the whole inner edges of which they are united
either by bone or by membrane; and as, at the same time, they
unite in the middle line, the roof of the palate is greatly pro-
longed, and the posterior nares are bounded below and at the
sides by the pterygoid bones. This arrangement is to be
found in no other Mammals, except some Cetacea, nor in any
other Vertebrata, except the Crocodiles. The mandible is
very slender, the ascending ramus, coroncid process, and angle
of the jaw, being obsolete. The articular surface of the con-
dyle is flat. The hyoid is placed far back beneath the posterior
cervical vertebra, and is connected with the skull only by
muscles. The thyroid and the cricoid cartilages are ossified.
The dorso-lumbar vertebre are complicated by the presence
of accessory articular processes. Well-developed clavicles are
present in the climbing Cyclothurus didactylus, but they are
incomplete, or absent, in the other species. In the manus, the
outer digit, or digits, are devoid of claws, and the weight of
the body, when the animal walks, is supported upon its outer
edge, which is frequently thick and callous. The pes has five
digits, each provided with a strong nail, and the sole rests
upon the ground.

The tongue is extraordinarily long and protractile; it is
not connected to the hyoid by the ordinary hyo-glossus mus-
cles; but long muscles, which are attached to the sternum
(sternoglossi), retract it, while it is protracted by the genio-
glossi and stylo-hyoidet.

288 THE ANATOMY OF VERTEBRATED ANIMALS.

Immense submaxillary glands extend back over the thorax,
and cover the tongue with a viscid secretion, when it is thrust
into the nests of the ants, upon which the Myrmecophaga
preys. The insects, entangled by thousands in this substitute
for birdlime, are then dragged back into the mouth of the
Ant-eater, and swallowed. ‘The pyloric portion of the stomach
is so exceedingly thick and muscular as to be comparable to
a gizzard. The brain presents numerous convolutions, and
has a large corpus callosum. ‘The anterior commissure is also
remarkably large. In the female, the uterus is simple, but has
a double os uter?. The placenta is said to be discoidal in
form in Myrmecophaga didactyla.

6. The group of the Sgwamata contains the single genus
Manis, species of which are found both in Africa and Southern
Asia. In these singular animals, the body is covered with
overlapping, horny scales, and they have the power of rolling
up like hedgehogs. In walking, the long claws of the fore-
foot are bent under, so that their dorsal surfaces rest upon the
ground, while the weight of the hinder part of the body is
thrown upon the flat soles of the hind-feet.

The skull is elongated, the premaxilla is small, and the
zygoma usually incomplete. The pterygoids are much elon-
gated and extend backward beyond the bullate tympanic
bones, but they do not unite in the middle line. The mandible
has no ascending ramus, and its condyle is flat. Air-passages
in the walls of the skull place one tympanum in communication
with the other and extend into the squamosal bone. There
are no clavicles. The “xiphoid” extremity of the sternum is
large, and may be produced into two long cornua, as in Lizards.
The mouth is toothless.

The large salivary glands extend on to the thorax. The
stomach is divided into a thin-walled cardiac sac, lined by a
dense epithelium, and a thick muscular pyloric portion. It
is always found to contain numerous stones. The placenta
appears to be diffuse and non-deciduate.

ce. The Tubudidentata are also represented only by a single
cenus, Orycteropus, which is a native of South Africa. The
body is hairy, provided with thoracic and inguinal teats, and
the ears are long, not short or rudimentary, as in the preceding
genera. In both the fore- and the hind-limbs, the foot rests
evenly upon the ground and mainly upon the plantar surfaces
ef the strong claws. The fore-foot has only four digits, in
consequence of the absence of the pollex, while the hind-foot
is pentadactyle.

THE EDENTATA LORICATA. 289

The skull has a complete zygoma and well-developed pre-
maxille. The lachrymal bone is large, and the lachrymal
foramen is situated upon the face. The tympanic bone is
annular, and the periotic mass so large, and enters so much
into the lateral walls of the skull, as to remind one of its pro-
portions in the Sauropsida. The mandible has an ascending
ramus. ‘The clavicules are complete.

The jaws are provided with teeth, the substance of which
is traversed by a great number of parallel vertical canals,
These teeth are rootless molars, and the greatest number
which has been observed is ;%, but the small anterior ones
fall out, reducing them to =. The hindermost, and the small
anterior ones, are simple cylinders, but the middle teeth pre-

‘sent a longitudinal groove on each side.

The submaxillary glands are very large. The stomach is
divided into a right and a left portion; the former having very
thick and muscular walls. The intestine has a cecum. It is
stated that the ductus arteriosus long remains open.

The two uteri open separately into the vagina. The pla-
centa is deciduate and discoidal.

d. In the Loricata, the dorsal region of the body is covered
by a carapace, composed of epidermal scales, and of suturally
united quadrate, or polygonal, scutes, which are dermal ossi-
fications, so that the whole structure is strictly comparable to
the dorsal shield of a crocodile. These are the only Mammals
in which such scutes exist. When fully developed, the dorsal
armor of one of these animals presents five distinct shields,
the edges of which permit of a certain amount of motion be-
tween them. One of these covers the head, and is called
cephalic ; another, nuchal, protects the back of the neck; a
third, scapular, covers the shoulders like a great cape; a fourth,
usually consisting of a number of tree and movable segments,
covers the posterior dorsal and lumbar region, as the thoraco-
abdominal shield; and the fifth, the pelvic, is attached by its
deeper surface to the ilia and ischia, and arches over the rump
like a half dome. The tail may further be invested by a series
of incomplete bony rings and scattered scales; and scutes are
distributed over the limbs. In one genus, Chlamydophorus,
the scutes are developed only in the pelvic region.

In the skull\the premaxille are well developed, and the
zygoma is complete. The mandibular ramus usually has a
well-developed ascending portion and coronoid process.
Clavicles are present. The fore- and the hind-feet rest upon

13

290 THE ANATOMY OF VERTEBRATED ANIMALS.

the ground evenly, and indeed the hind-limbs are usually
plantigrade, or nearly so; but, in the singular genus Zoly-
peutes, the fore-foot is supported upon the extremities of the
long nails. The pollex is always present in the fore-foot, but
the fifth digit sometimes becomes rudimentary. There are
always five toes in the hind-foot.

In the genus Huphractes, each premaxilla contains a single
tooth, which, consequently, is an incisor.

This group contains two divisions, the Dasypodide and
the Glyptodontide ; both are South American, but the former
is chiefly composed of living animals, while the latter only
contains an extinct genus.

The Dasypodide are what are commonly known by the
name of Armadillos. In this division the thoraco-abdominal
shield, when present, as it is in all the genera except Chla-
mydophorus, cousists of, at fewest, three, and, at most, thir-
teen, transverse movable zones of scutes.

In the skull, the ends of the nasal bones project beyond
the level of the premaxille, so that the nasal aperture looks
more or less downward. ‘The premaxillz have a considerable
size, and articulate largely with the nasals. The anterior part
of the jugal arch offers, at most, a rudimentary downward pro-
longation. The mandibular symphysis has but a moderate
length, and the posterior alveoli of the mandibles do not ex-
tend along the inner face of the ascending portion of the
ramus of the jaw.

The teeth of the upper and lower jaws alternate, and
hence their grinding surfaces wear down into ridges.

The odontoid vertebra is anchylosed with a greater or
smaller number of its successors. The cervical vertebrae
which follow these have peculiar accessory articular surfaces ;
and the hinder dorsal and the lumbar vertebrz are also pro-
vided with accessory articular facets and processes. A number
of the anterior caudal vertebre are always anchylosed with one
another, and with the true sacrals, to form the long sacrum;
and the transverse processes of some of these caudal vertebrze
abut against the inner surfaces of the ischia, and become an-
chylosed therewith.

The first rib is broad and flattened, and the anterior piece
of the sternum is expanded. The succeeding vertebral ribs
are connected by ossified sternal ribs with the sternum, and
these are articulated, not only with the sternum, but with one
another.

In the carpus, the cuneiform bone bends round the unci-

THE EDENTATA LORICATA. 291

form, and articulates with the fifth metacarpal, when that
bone is present. The ungual phalanges of the manus are
long and pointed. The femur has a third trochanter, and
the four inner metatarsals are much longer than they are
broad.

The division of the Glyptodontide contains the single
genus Glyptodon, which is essentially a large armadillo; but
it departs, in some respects, not only from all these animals,
but from ‘all other Mammalia, and even stands alone among
the Vertebrata.

The carapace covers the whole body, but presents no
movable thoraco-abdominal zones, inasmuch as it consists of
polygonal plates firmly united together, and fringed by a mar-
gin of scutes with raised conical surfaces.

The nasal bones are short and broad, and their free ends
do not project so far as the premaxillz ; whence the anterior
nasal aperture looks slightly upward as well as forward. The
premaxillz, however, are very small bones, and, if they unite
with the nasals at all, do so for a very short distance. The an-
terior portion of the jugal arch gives off a great downward pro-
cess. The mandibular symphysis is very long, and the posterior
alveoli of the mandible are situated upon the inner face of the
very high perpendicular part of the ramus. The teeth are
- trilobed, two deep grooves excavating their inner and their
outer surfaces. And, as the crowns of those of each jaw are
placed opposite each other, they are worn flat.

The last cervical and the anterior dorsal vertebre are
anchylosed together into a single “tri-vertebral” bone which
moves by a hinge-joint upon the third dorsal. This and the
succeeding dorso-lumbar vertebree are immovably united, and,
for the most part, anchylosed, together. The head of the first
rib is engaged in the socket furnished to it by the tri-vertebral
bone in such a manner as to be immovable, and the rib is not
flat, but rounded and columnar.

In the carpus, the cuneiform bone articulates with the
fourth, as well as with the fifth metacarpal, the latter bone
being entirely supported by the cuneiform. The metacarpals
and phalanges are all very short and broad. The pollex is
rudimentary, while the fifth digit is fully developed.

The supra-condyloid ridge of the femur is not distinct from
the third trochanter, even if the latter can be said to exist at
all. The metatarsal bones are as broad as they are long, or
broader; and, as in the fore-foot, the majority of the phalanges
are comparatively short and truncated.

292 THE ANATOMY OF VERTEBRATED ANIMALS.

Tur Non-precipuaTe Mammaria.—lI. Uneurata.—A large
number of the non-deciduate Mammalia are conveniently com-
prehended under the title of the Ungulata, though it may be
open to question whether the group thus named represents a
single order, or more than one.

In all the Ungulata the placenta is either diffuse, that is to
say, the villi are scattered evenly over the surface of the
chorion; or it is cotyledonary, in which latter case, the villi
are accumulated in distinct patches on the chorion. These
patches are called cotyledons.

All Ungulata have milk-teeth, succeeded vertically by
teeth of the permanent set. The teeth consist of enamel,
dentine, and cement, and the grinders have broad crowns,
with tuberculated, ridged, or folded enamel.

Clavicles are never present. The limbs have not more
than four complete digits. The ungual phalanges are clothed
in obtuse horny sheaths, which are commonly very, thick and
go by the name of hoofs. Upon these the weight of these
quadrupeds is usually supported, whence they have been
called unguligrade. Some few, however, rest the weight of
the body upon the under surfaces of the phalanges, or are
digitigrade. 'The metacarpal and metatarsal bones are elon-
gated, and take a vertical, or much inclined position.

In the female, the mamme are either few in number, when
they are inguinal in position; or numerous, when they are dis-
posed in two rows along the abdomen.

The intestine is very generally provided with a czecum of
considerable size.

The cerebral hemispheres always exhibit convolutions, .
which are usually very numerous; and, when the brain is
viewed from above, the surface of the cerebellum is largely
uncovered.

The Ungulata are divisible into the Perissodactyla and
the Artiodactyla, though it is probable that the attempt to
define these groups will break down with the increase of our
knowledge of fossil forms.

1. In the Perissodactyla, the number of the dorso-lumbar
vertebre is not fewer than twenty-two. The third digit of
each foot is symmetrical * in itself, and the toes of the hind-
foot are odd in number (Fig. 93, B). The femur has a third
trochanter (Fig. 100—*). The two facets upon the front face
of the astragalus are very unequal; the less articulating with
the cuboid bone.

* Or at least very nearly so.

THE PERISSODACTYLA. 293

In the skull, the tympanic bone is small; and, as in sun-
dry other Mammals, the root of the pterygoid process of the
sphenoid is perforated by an aperture or canal.

The posterior premolar teeth are, generally, very like the
molars. The stomach is simple, and the caecum exceedingly
large.

‘The teats are inguinal, or situated in the groin. When
the head is provided with horny appendages, they are entires
ly epidermal and devoid of a bony core; and they are placed
in the middle line of the skull.

Fia. 93.—A, Front aspect of the left tarsus of a Horse—1. Caleaneum. 2. Astragalus. &
Naviculare. 4. Ectocuneiform. 5. Cuboides.

B, Posterior aspect of the left metatarsus of a Horse—1. The metatarsal of the third digit,
2,8. The metatarsals of the rudimentary digits.

The Perissodactyla consist of the existing families Kguida,
Khinocerotide, and Tapiride, and of the extinct Palcothe
ride and Macrauchenide. :

294 THE ANATOMY OF VERTEBRATED ANIMALS.

fia, 94.—A, right fore-foot of a Horse.—1. Radius. 2. Groove in the front face of the radi.
us. 8. Scaphiides. 4. Lunare. 5. Cuneiforme. 6, Pisiforme. 7 Magnum. 8. Un-
ciforme. 9. Metacarpale, 7z. 10. Metacarpale, 7. 11. Sesamoid bones in the liga.
ments at the back of the metacarpo-phalangeal articulation, 12. Proximal phalanx (fet-
ter-bone). 13. Middle phalanx (coronary). 15. Distal phalanx (coffin-bone). 14. Sesa-
moid bone in the tendon of the flexor perforans (called “ nayicular” by Veterina-
rians).

, left hind-foot of a Horse.—1. Tibia. 2. Caleaneum. 8. Astragalus. 4. Cuboid. 5. Na-

vicular, or scaphoid. 6. Ectocuneiform. 7. Metatarsale, diz. 8. Metatarsale, iv. 9, 11,
12. Phalanges. 10, 14. Sesamoids.

TT o-oo See ee

THE PERISSODACTYLA. 295

a. The Lyuide, or Horses and Asses, have one toe on
each foot—the third—much longer and larger than the rest.
The latter are represented only by their metacarpal or meta-
tarsal bones, the inner and outer toes being absent, or repre-
sented by mere ossicles (as rudiments of their metacarpals or
metatarsals) in all existing Hguide. But, in the extinct Hip-
parion, the second and fourth digits were complete, though
small and like dew-claws; while the miocene Anchitherium,
which most nearly approaches the Palwotheride, has the lat-
eral toes much larger, and taking their share in supporting
the weight of the body.

The dental formula is ¢. =~ ¢. “i pm. 7m. =. The
tooth here counted as the first premolar may be a milk-tooth,
as it appears to have neither predecessor nor successor, and
soon disappears.

The molar teeth present an outer wall, which is bicrescen-
tic in transverse section; and two inner ridges, which are
curved more or less inward and backward, and correspond re-
spectively with the anterior and the posterior crescents of the
outer wall. The valleys may be more or less completely filled
up with cement, which also coats the tooth. The incisors are
similar in form in each jaw, and in Aguus and Hipparion their
crowns present a wide and deep median cavity, formed by a
fold of the enamel.

These are the distinctive characters of the Hquide. It
may be useful to add some special details respecting the anat-
omy of the Horse as a familiar example of the perissodactyle
group.

The Horse has seven cervical vertebre, twenty-four dorso-
lumbar (eighteen or nineteen of which are dorsal), five sacral,
and about seventeen caudal vertebre. The atlas has very

Fia. 95.—A cervical vertebra of a Horse——1. The rudimentary spine. 2,8. The pre- and
post-zygapophyses. 5. The convex anterior face of the centrum. 9. Its concave pos-
terior face. 6, 7. The transverse processes and rudimentary ribs.

Bvricl
We

ofh
oF Se

(apr,

296 THE ANATOMY OF VERTEBRATED ANIMALS.

wide lateral processes, the faces of which look obliquely down-
ward and forward, and upward and backward. The centra
of the other cervical vertebree are much elongated, strongly
convex in front, and correspondingly concave behind. The
neural spines are obsolete in all but the seventh. The liga-
mentum nuche is a great sheet of elastic tissue, which extends
from the spines of the anterior dorsal vertebrz to the occiput,
and is fixed, below, into the neural arches of the cervical ver-
tebree.

In the dorsal region, the opisthoccelous character of the
centra of the vertebre gradually diminishes, though the ante-

|

{

a

Fie. 96,—The skeleton of the Horse.

THE HORSE. 297

rior face of the centrum of the last lumbar is still distinctly
convex. The spines of these vertebrz increase in length to :
the fourth or fifth. The spine of the sixteenth is vertical, /i+~
those in front inclining backward, and those behind a little
forward.

In none of these vertebrze do the prezygapophyses bend
round the postzygapophyses of the vertebra in front, as is
often the case in the Artiodactyla. The transverse processes
of the penultimate, and of the last, lumbar vertebre presentjz,4
concave facets upon their posterior margins, which articulate 2.
with convex facets developed upon the anterior margins of ac.
the last lumbar and first sacral vertebrz respectively.

In the skull, the plane of the supra-occipital is inclined

upward and forward, and gives rise to the middle part of a
transverse ridge which is continued at the sides into the squa-
mosal, The ridges which limit the origins of the temporal
muscles above, unite in the middle line posteriorly, and thus
produce a low sagittal crest. The orbit is bounded behind by
the united post-orbital processes of the frontal and the jugal.
The lachrymal aperture lies in the orbit. The nasal bones
unite, for a short distance only, with the premaxilla. There
is no preenasal bone. The posterior margin of the palate is
opposite the penultimate molar tooth. The glenoidal surface
is transversely elongated and convex from before backward.

The tympanic bulla is not very large, and is rugose inferi-
orly. It is not anchylosed with the surrounding bones, The
post-tympanic process of the squamosal does not approach
the post-glenoidal process of the same bone, below the meatus
auditorius.

The proper mastoid process is distinct, but short. There
is along and strong paramastoid developed from the ex-oc-
cipital.

_ The rami of the mandible are anchylosed at the symphysis.
The perpendicular part of each ramus is long, the condyle
transverse and convex from before backward, and the narrow
coronoid process rises far above the level of the condyle. In
a longitudinal section of the skull the cerebral chamber lies
almost altogether in front of that for the cerebellum.

The structure of the limbs of the Horse is such as might
be expected from its preéminent cursorial powers.

That excessive development of the epidermis which gives
rise to a nail takes place, in the Horse, not only upon the
dorsal surface of the terminal joint of the digit, but upon its
ventral surface and sides, and thus produces a hoof.

298 THE ANATOMY OF VERTEBRATED ANIMALS.

The animal is supported by these greatly-developed nails,
and hence is said to be unguligrade. The long axis of its
phalanges are greatly inclined to the surface upon which it
stands, while those of the metacarpals and metatarsals are per-
pendicular and greatly elongated. ‘The wrist of the Horse
thus comes to occupy the middle of the length of its fore-leg,
and constitutes what is improperly called the “knee.” The

Fic, ¥7 --Longitudinal median section of the foot of a Horse—13, 14,18. The three pha-
lunges. 16. Thenayicular sesamoid. 5. The flexor perforatus. 6. The flexor perforans.
19. The hoof.

heel is similarly raised to the middle of the hind-leg, and is
termed the “hock.” The forearm and the leg are free, but
their motions are almost restricted to an antero-posterior
plane. The forearm is fixed in the prone position. The arm
and thigh are closely applied to the sides of the body and en-
closed in the common integument, so as to be capable of very
little proper motion. At the same time, the axis of the hu-
merus is inclined obliquely backward and downward, at right
angles with the long axis of the scapula; and that of the
femur obliquely forward and downward at right angles with
that of the os innominatum ; and the long axes of both these

re Po

elite | at ah Sane

e

<p re eS |

THE HORSE. 299

bones make a great angle with those of the forearm and leg
respectively. Hach limb thus forms a sort of double C spring,
upon the top of which the weight of the body is supported—
in the hind-limbs by means of the solid connection of the ilia
with the sacrum; in the fore-limbs, by the great muscular
slings formed by the serratus magnus and the levator anguli
scapule.

The scapula is long and narrow;
the low spine has no acromion; the
coracoid process is small, and there is
no clavicle. :

The head of the humerus looks
backward, and the distal articular sur-
face of the bone is completely gingly-
moid, The two bones of the ner
chium are anchylosed ; the shaft of the
ulna becomes exceedingly slender, and
its small distal end is distinguishable
only with difficulty. The articular sur-
face for the carpal bones is, therefore,
almost wholly furnished by the radius,
There are seven carpal bones, the tra-
pezium being obsolete. A line pro-
longing the axis of the third metacar-
pal and that of the os magnum does
not pass through that of the lunare,
but corresponds more nearly with the
junction between scaphdides and
lunare. ,
The pollex and the fifth digit are Fie. 98—Front view of the right
suppressed, or represented only by mi- $27Pus of a Horse-—1. Cubel-
nute nodules of bone, and the only _ phiides. 4. Fistor’:
complete digit is the third; the sec- pee Fe ee
ond and the fourth being represented
only by the splint-like metacarpal bones. The third meta-
carpal, which is somewhat flattened from before backward, is
nearly symmetrical in itself. Careful observation, however,
shows the inner moiety to be rather the broader.

There are two large sesamoid bones (the greater sesamoids)
developed in the ligaments which connect the metacarpal with
the basal phalanx; and one transversely-elongated sesamoid
gives attachment to the tendon of the perforating flexor, and
lies upon the ventral aspect of the joint between the middle
and the distal phalanx,

a

SO
=

300 THE ANATOMY OF VERTEBRATED ANIMALS.

The ossa innominata are elongated, and their long axes,
on the length of which depends the proportional size of the
“quarter” of a Horse, form an acute angle with the spine.
The crests of the ilia are wide and directed transversely, and
the symphysis pubis is very long.

Fie, 99.—The ossa innominata of a Horse viewed from the left side and behind.—1. ‘The
crest of the illum. 2. The surface by which it articulates with the sacrum. 4. The
acetabulum, 6. The ischium.

The femur has a large third trochanter (*, Fig. 100), into
which the glutcus maximus is inserted. Its head presents a
deep pit for the round ligament, and there is a peculiar and
very characteristic fossa (*°) on the inner and posterior face of
the distal moiety of the bone.

The proximal end of the fibula is reduced to a mere rudi-
ment; its shaft is not represented by bone; and its distal end
is anchylosed with the tibia, and has the appearance of being
an external malleolar process of that bone. The distal end
of the tibia presents two deep, obliquely-directed concavities,
which correspond with the convexities of the astragalus.

There are six or seven tarsal bones, according as the ento-
and meso-cuneiform bones remain distinct or become anchy-
losed. The astragalus (Fig. 93 A, 94 B) is extremely charac-
teristic. It presents two convex ridges separated by a deep
fossa, and directed obliquely from behind and within, forward
and outward, to the tibia; and it has a nearly flat distal face,

THE MUSCLES OF THE HORSE. 301

not borne upon any distinct neck, which articulates almost
wholly with the naviculare, presenting only a very small facet

to the cuboid.

The naviculare and the ecto-cunei-
form are peculiarly broad and flattened
in form (Fig. 93 A, 94 B).

The metatarsus and digits repeat the
arrangements of the fore-limb; but the
principal metatarsal is more slender in
its proportions, and is flattened from
side to side rather than from before back-
ward (Fig. 93 B, 94 B).

As might be expected, the principal
peculiarities of the muscular system of
the Horse are to be observed in the
limbs.

The serratus magnus and the levator
anguli scapule (which really form one
muscle), together with a sterno-scapu-
taris, form the great sling already men-
tioned, by which the weight of the fore-
part of the body is transmitted to the
anterior extremities. The power of
abduction is hardly needed by a purely
cursorial animal; hence the deltoid is
reduced to its scapular portion, which is
very small, On the other hand, the
pro- and re-tractors, the flexors and ex-
tensors, are well developed. The supra-
and infra-spinatus are large. There is
a great cephalo-humeralis, answering to
the clavicular portions of the human
sternomastoid and of the deltoid, which
run into one another, in consequence of
the total absence of the clavicle. The
anterior portion of the sternomastoid is
fixed to the mandible, and thus becomes
“¢ sternomaxillary.”

The latissimus dorsi and teres mus-

Fie. 100.—A, Left femur of a

Horse, posterior view.—
1. Head. 2 Great tro-
chanter. 8. Third tro-
chanter. 4, Lesser tro-

5. Pit for round
10. Fossa,

chanter.
ligament.
11. Condyles.

cles are very large, as are the flexors and extensors of the

antibrachium.

The supinators and pronators are wanting; but there is
a distict extensor minimi digiti, the tendon of which unites

with that of the extensor communis.

Radial and ulnar ex:

802 THE ANATOMY OF VERTEBRATED ANIMALS.

tensors of the carpus are also present. The flexor perforatus
has only a single tendon, which splits, and is attached, as
usual, to the sides of the middle phalanx. The flexor per-
forans also has only a single tendon, which pierces the
former, and is inserted into the lesser sesamoid and the distal
phalanx.

The interosset of the third digit are represented only by
the ligaments which connect the greater sesamoid bones with
the metacarpal, and in which a few muscular fibres are some-
times found. There are said to be two others, one for each
lateral metacarpal, and a lumbricalis.

In the hind-limb, the femoral muscles are in the Horse
the same as in Man, but enormously developed. There is
no tibialis anticus, peroncus longus, or brevis, nor any tibialis
posticus.

The extensor longus digitorum has a head which arises
from the external condyle of the femur; there is a simple ex-
tensor brevis.

The flexor hallucis and flexor digitorum perforans unite
into the single perforating flexor tendon for the distal phalanx ;
while the perforated tendon is the termination of that of the
plantaris, which passes over a pulley furnished by the cal-
caneum.

The deciduous or milk dentition of the Horse has the fol-
lowing formula: di. =, d.c. = d.m.73. Itis complete at birth,
with the exception of the outer incisors, which appear before
the foal is nine months old. The incisors have the same struct-
ure as in the adult. The canines and first deciduous molars
are simple and very small, the canines being smaller than the
molars. In the upper jaw, the other deciduous molars all have
the same structure. The outer wall of the tooth is bent in
such a manner as to present, from before backward, two con-
cave surfaces separated by a vertical ridge. From the anterior
end, and from the middle, of this outer wall, two lamine of
the crown pass inward and backward, so as to be convex in-
ward and concave outward, and thus to include two spaces
between themselves and the outer wall. From the inner sur-
face of the hinder part of each of these crescentic laminz a
vertical pillar is developed, and the inner surface of the pillar
is grooved vertically. The outer wall, the laminz, and the
pillars, are all formed of dentine and enamel, thickly coated
with cement. The attrition which takes place during mastica-
tion wears down the free surfaces of all these parts, so as, in
the long-run, to lay bare a surface of dentine in the middle of

~

THE TEETH OF THE HORSE. 303

each, surrounded by a band of enamel, and, outside this, b
the cement with which the interspaces are filled. The band
of enamel is simple and unplaited. The general pattern of
the worn surface may be described as consisting, externally,
of two longitudinal crescents, one behind the other, and with
their concavities turned outward which arise from the wear
of the wall; internal to these, of two other crescents, partly
transverse in direction, and connected by their anterior ends
with the wall, which arise from the wear of the laminz; and
attached to the inner surface of these, two hour-glass-shaped
surfaces, produced by the wear of the grooved pillars.

In the mandible, the structure of the molars and the re-
sulting pattern are quite different. The outer wall presents
two convex surfaces separated by a longitudinal depression,
and thus reverses the conditions observable in the upper
molars. The result of the wear of this is, necessarily, two
crescents, the concavities of which are turned inward. A
vertical pillar, longitudinally grooved on its inner face, is de-
veloped on the inner face of the tooth at the junction of the
anterior and posterior crescents, and gives rise to a deeply-
bifurcated surface when worn. A second smaller pillar ap-
pears in connection with the inner face of the posterior end
of the outer wall.

Thus the grinding surface of the upper molars may be rep-
resented by four crescents with two inner pillars; and that
of the lower molars by two crescents with two inner pillars.
The upper crescents are concave outward; the lower concave
inward; and by this arrangement, together with the unequal
wear of the dentine, enamel, and cement, a permanently un-
even triturating surface is secured.

Asis the general rule among Mammals, the first permanent
molar is the first permanent tooth which appears (unless the
eruption of the inner incisor be contemporary with it), and it
comes into place and use long before the deciduous molars are
shed and replaced by the premolars. Hence, when the last
premolar comes into place as a fresh and unworn tooth, the
first molar, which lies next to it, is already considerably worn.
This disparity of wear is maintained for a long time, and
furnishes a very useful means of distinguishing the last pre-
molar from the first molar in the adult, when, as in the Horse,
the premolars and molars are very similar.

The first deciduous molar usually falls out when the first
premolar appears, and is not replaced; but it is occasionally
retained. All the other milk-teeth have successors, and there

304 THE ANATOMY OF VERTEBRATED ANIMALS.

are three permanent molars. Consequently the dental formula
of the adult Horse is

pee 1—1 3°3 3°38

Liat. gains IN. 535 ae

The permanent canines are the last teeth to be fully de-
veloped, and, in the mare, they do not often make their appear-
ance. ‘The upper canines are distant from the outer incisors,
while the lower canines are quite close to them. In both jaws
there is a wide interval, or diastema, between the canines and
the premolars.

The deep valley of the incisor teeth becomes filled up with
masticated matter, and thus the dark “mark” is produced.
As the incisors wear down, the mark changes its form in con-
sequence of the differences in the transverse section of the
valley at different points; and eventually, when the wear has
extended beyond the bottom of the valley, it disappears. The
presence or absence of the “mark” thus serves as an indica-
tion of age. The structure and patterns of the grinding sur-
faces of the permanent molars are essentially the same as those
of the milk-molars; but the enamel becomes more or less
plaited ; and, at an advanced period of life, the development
of the long teeth is completed by the formation of roots. It
is important to notice that the last molar of the Horse is not
more complex in its structure than the other molars, and that
the last milk-molar is not more complex than the premolar
which succeeds it.

The alimentary canal of the Horse is about eight times as
long as the body. The stomach, simple in its form, presents
a cardiac and a pyloric division, which are sharply distin-
guished by the dense epithelium which lines the inner surface
of the former.

The caecum is enormous, having fully twice the volume of
the stomach. There is no gall-bladder. A cartilage is de-
veloped in the septum of the heart. There is no Eustachian
valve, and only one anterior cava remains. The aorta divides
immediately after its origin into an anterior and a posterior
trunk; the latter becomes the thoracic aorta; the former is
the source of the arteries for the head and the anterior ex
tremities, giving off first the left subclavian, and then as
an “innominata” supplying the right subclavian and the
carotids.

The trachea divides into only two bronchi, no accessory
bronchus being given off to the right lung. In the brain the
following points : are worthy of notice: The medulla oblongata

=

THE VISCERA OF THE HORSE. 305

presents corpora trapezoidea. The flocculi do not project at
the sides of the cerebellum, and the vermis and lobes of the
cerebellum are unsymmetrically convoluted. The cerebral
hemispheres are elongated and subcylindrical, and do not
overlap the cerebellum when the brain is viewed froin above.
The sulci are very deep, and separate numerous gyri, upon the
upper and outer surfaces of the hemispheres. The uncinate
gyrus (or natiform protuberance) and the region which answers
to the insula are not hidden by the overlapping of the con-
volutions in the lateral aspect of the brain. The Sylvian fis-
sure is indicated. The corpus callosum is large, and the an-
terior commissure is of moderate size. The posterior cornu
of the lateral ventricle is wanting.

Large air-sacs are connected with the Eustachian tubes.

The testes pass into a scrotum, but the unguinal canal re-
mains permanently open.

The prostate is single. Cowper’s glands are present, and
there is a large uterus masculinus. The large penis is shel-
tered within a prepuce and is retracted by a special muscle,
which arises from the sacrum.

The uterus is divided into two cornua, and the vagina of
the virgin mare is provided with a hymen. The period of
gestation is eleven months. The yelk-sac of the foetus is
small and oval. The allantois spreads over the whole interior
of the chorion and covers the amnion, which is vascular. The
minute villi which it supplies with vessels are evenly scattered
over the whole surface of the chorion.

The existing guide are naturally restricted to Europe,
Asia, and Africa; and are distinguished into the Horses,
which have horny patches on the inner sides of both pairs of
limbs—above the wrist in the fore-limb and on the inner side
of the metatarsus in the hind-limb; and the Asses, which
possess such callosities only on the fore-limbs,

Fossil remains of “guide are abundant in the later ter-
tiary deposits of Europe, Asia, and the Americas; but the
group is not known to be represented earlier than the miocene,
or later eocene, epoch.

The Hquide are among the very few groups of Mammalia,
the geological history of which is sufficiently well known, to
prove that the existing forms have resulted from the gradual
modification of very different ancestral types. The skeleton
of the older pliocene and newer miocene Hipparion very
closely resembles that of an Ass, or a moderate-sized Horse.
There is a curious depression on the face in front of the orbit,

306 THE ANATOMY OF VERTEBRATED ANIMALS.

somewhat like that which lodges the “larmier” of a stag
(traces of which are observable in some of the older species
of Hquus); otherwise the cranium is altogether like that of
a Horse. Again, the shaft of the ulna is very slender, but it
is larger than in the Horse, and is distinctly traceable through-
out its whole length although firmly anchylosed with the
radius. The distal end of the fibula is so completely anchy-
losed with the tibia, that, as in the Horse, it is difficult to
discern any trace of the primitive separation of the bones.
But, as has been already mentioned, each limb possesses three
complete toes—one strong, median, and provided with a large
hoof, while the two lateral toes are so small that they do not
extend beyond the fetlock-joint. In the fore-limb, rudiments
of the first and fifth toes have been found.

The teeth are exceedingly like those of the Horse, but the
crowns of the molars are shorter; and, in the upper jaw, that
which, in the true Horses, is a large fold of the inner face of
the tooth becomes a detached pillar. The smaller plications
of the enamel are also more numerous, close-set, and compli-
cated. On the outer face of the lower milk-molars there is a
column such as exists in the Stags. Of this a rudiment exists,
as a fold, in the corresponding teeth of the existing Horse,

In the genus Anchitherium, all the known remains of
which are of older miocene (and, perhaps, newer eocene) age,
the skeleton in general is still extraordinarily like that of a
Horse. The skull, however, is smaller in proportion than in
the Horse, and the jaws are more slender. The hindermost
molar tooth is situated farther back under the orbit, and the
orbit itself is not completely encircled by bone, as it is in the
Horses and Hipparions,

The shaft of the ulna is stouter than in H/ipparion, and is
less closely united with the radius. ‘The fibula appears, at any
rate in some cases, to have been a complete though slender
bone, the distal end of which is still closely united with the
tibia, though much more distinct than in the Hipparions and
the Horses. In some specimens, however, the middle of the
shaft seems to have been incompletely ossified. Not only are
there three toes in each foot, as in Hipparion, but the inner
and the outer toes are so large that they must have rested
upon the ground. ‘Thus, so far as the limbs are concerned, the
Anchitherium is just such a step beyond the f/ipparion, as
the Hipparion is beyond the Horse, in the direction of a less
specialized quadruped. The teeth are still more divergent
from the Equine type. ‘The incisors are smaller in proportion,

HIPPARION AND ANCHITHERIUM. 307

and their crowns lack the peculiar pit which characterizes
those of Hguus and Hipparion. The first grinder is propor-
tionately much larger, especially in the upper jaw, and lke
the other six has a short crown and no thick coat of cement.
The pattern of their crowns is wonderfully simplified. The
fore and hind ridges run with but a slight obliquity across the
crown, and the pillars are little more than enlargements of the
ridges, while in the lower jaw these pillars have almost disap-
peared, But the foremost of the six principal grinders is still
somewhat larger than the rest, and the posterior lobe of the
last lower molar is small, as in the other Aqguide.

In all those respects in which Anchitherium daparts from
the modern Equine type, it approaches that of the extinct
Paleotheria ; and this is so much the case that Cuvier con-
sidered the remains of the Anchitherium with which he was
acquainted to be those of a species of Palcwotherium.

6. In the Rhinocerotide the second, third, and fourth toes
are nearly equally developed in both the fore- and the hind-
feet.

at 0

: . . e 0:0 ‘0 ; 4°4 3 3
The dental formula is 7. = or 4. <5 ¢. 55 p.™. aq ™ 5%

But the teeth differ from those of the Horse in many other
respects besides the number of the incisors and the absence of
canines. Thus, the upper incisors differ greatly in form from
those which are situated in the lower jaw; and, in some spe-
cies, incisors are absent. Their crowns are not folded as in
the Horse. The peculiarities of the grinding teeth will be
mentioned below.

The skin is very thick and may be converted into a jointed
armor; the hair is scanty. The upper lip is much produced
and is very flexible. In some species one, or sometimes two,
horns are attached in the middle line to the nasal or frontal
bones. But these horns are formed, as it were, by agglomer-
ation of a great number of hair-like shafts.

The distal phalanges of the tridactyle feet of the Rhinoce-
ros are invested by small hoofs; but these do not entirely
support the weight of the body, which rests, in great measure,
upon a large callous pad developed from the under face of the
metacarpal and metatarsal regions; these are much shorter
than in the Horse.

The dorso-lumbar vertebre are twenty-two or twenty-three,
of which twenty are dorsal. There are four sacral and twen-
ty-two caudal. The cervical vertebre, as in the Horse, are
strongly opisthoccelous, and the transverse processes of the

308 THE ANATOMY OF VERTEBRATED ANIMALS.

last lumbar articulate with those of the penultimate lumbar
and with the sacrum.

The skull differs from that of the Horse in the absence of
any frontal or zygomatic processes in consequence of which
the orbit and temporal fossa form one cavity. The nasals are
immense, and are separated from the premaxillz by a wide
extent of the maxilla on each side. The premaxille are rela-
tively small and reduced to little more than their palatine por-
tions. The glenoidal surface of the mandible is transverse
and convex. ‘The squamosal sends down an immense post-
glenoidal process, which is longer than either the post-tym-
panic or the paramastoid. It unites with the post-tympanic
to form a kind of false auditory meatus, in the absence of any
proper ossified canal of that kind. The periotic and the tym-
panic bones are anchylosed, the tympanic being a mere irreg-
ular hoop of bone. The pars mastoidea is completely hidden
by the junction of the short post-tympanic with the long par.
amastoid. ‘The hinder margin of the bony palate is opposite
the middle of the antepenultimate molar.

The mandibular condyle is transverse and conyex. The
perpendicular portion of the ramus is large, and the coronoid
process ascends slightly above the condyle. In a vertical and
longitudinal section of the skull, the form of the cerebral cay-
ity is seen to be similar to that of the Horse. The inner and
outer tables of the bony roof of the skull are separated by
great air-cavities.

The spine of the scapula has no acromion, but gives off a
strong recurved process from the middle of its length.

The radius and ulna are complete, but are anchylosed.

The carpus has the eight ordinary bones. In the manus
the digits ii., ili., iv., are complete, and a bony tubercle articu-
lated with the outer facet of the cuneiforme represents digit
v. The digit iii. is largest and longest, and its phalanges are
symmetrical in themselves; those of the digits ii, and iy. are
not symmetrical in themselves. The terminal phalanges have
somewhat the form of the coffin-bone of the Horse.

The ilia have wide, transversely-directed crests, as in the
Horse. The femur is provided with avery strong third tro-
chanter. The tibia and the fibula are complete, and the tarsus
has the ordinary seven bones. ‘The pulley of the astragalus
is not very deeply grooved, and is hardly at all oblique. The
facet for the cuboid is very small. The metatarsals resemble
the metacarpals in their number and symmetry, but there is
no rudiment of the fifth.

THE RHINOCEROT. 309

In some species of Rhinoceros there are $= incisors in the
. . 1 a | 1 Ya | ° . . .
milk detention, and ,, or 7 incisors in the permanent denti-

tion. In the latter the upper incisors are large, long-crowned
teeth, very unlike the lower ones, of which it seems probable
that only one pair, in any case, are permanent teeth. In some
Rhinoceroses, as has been already stated, the adult is devoid
of incisor teeth.

There are no canines in either dentition. Of the four milk-
molars, the first, as in the Horse, is smaller than the others,
and is not replaced. The structure of both the upper and the
lower molars is substantially the same as in the Horse, but the
roots are developed much sooner; the laminz of the upper
molars take a much more transverse direction ; the laminz of
the upper molars do not develop pillars, though accessory
crests may be developed from the two faces of the posterior
lamina; the lower molars have no pillars; and the cement
does not fill up the valleys between the wall and the lamine.

The cardiac division of the simple, though large stomach,
is lined by a white callous epithelium, as in the Horse, The
small intestine presents large processes or tags, half an inch
long or more, upon which the true villi are borne. The
cecum is very large, and the colon enormous. There is no
gall-bladder. The heart and brain are very similar to those
of the Horse.

The male can hardly be said to have a scrotum, as the
testes lie close to the abdominal ring. A prostate, vesiculze
seminales, and Cowper’s glands, are present. The long penis
has a mushroom-shaped glans, and the animal is retromingent.
The cornua uteri are proportionately longer than in the mare.
The teats are two and inguinal in position. The characters
of the foetal membranes and the nature of the placentation are
unknown.

At the present day the genus &hinoceros is confined to
Africa and Asia. The African species all have two horns,
a nearly smooth skin, and the adult has no incisors. The
Asiatic species have one horn only (except that of Sumatra,
which has two). The skin is marked out by deep folds into
shields, and the adults have well-developed incisors.

Rhinoceroses are known in the fossil state as far back as
the miocene epoch. WR. tichorhinus, with the nasal septum
ossified, and a covering of long woolly hair, inhabited Europe
and Asia during the cold of the glacial epoch. A. incisivus
had four digits in the manus, and larger incisor teeth than any

310 THE ANATOMY OF VERTEBRATED ANIMALS.

existing species. Jt. hexaprotodon had more numerous incis-
ors than any other species.

c. In the Zapiride there are four toes on the front-foot,
though the ulnar digit does not reach the ground. ‘The hind-
foot has three toes.

° A aed) ies | 4°4 3° 3

athe dental formula.is¢, soyiGi gay .. g5 le ae

The molar teeth each present two transverse, or slightly-
oblique ridges, connected by a low wall externally.

The skin is soft and hairy, and the muzzle and snout are
prolonged into a short proboscis.

The Tapirs have twenty-three or twenty-four dorso-lumbar
vertebrae, of which nineteen or twenty are usually dorsal.
The centra of these vertebrae, and the transverse processes of
the last lumbars, have the same peculiarities as those of the
Horse and Rhinoceros. There are seven sacral and about
twelve caudal vertebree. The skull is partly Rhinocerotic,
partly Equine, in its characters. Thus there is a sagittal crest
—the post-tympanic processes are large, but they are not so
long as the paramastoids, and they do not unite with the post-
elenoidal processes beneath the meatus. In these respects
the Tapir is Horse-like, but in the following it is more Rhino-
cerotic.

Thus the tympanic is quite rudimentary; the post-glenoid-
_ al process is larger than in the Horse; the orbit is not sepa-
rated from the temporal fossa; the nasals are widely sepa-
rated from the premaxillz; the premaxillz are very small, and
are early anchylosed.

The hinder margin of the osseous palate is opposite the
anterior edge of the penultimate molar. The mandibular rami
unite in a very long symphysis; the ascending portion of the
ramus is large, and projects backward with a convex edge in
a remarkable manner. There is a high coronoid process.

In the fore-limb, the scapula has no acromion, and the
coracoid is a mere tubercle. The supraspinous fossa is very
much larger than in the Horse or Rhinoceros. The radius and
the ulna are complete, but not movable upon one another.
Although, by the completion of the fifth digit, in addition to
the second, third, and fourth, there are four digits in the
manus, the Perissodactyle character is manifested by the fact
that the third is longest, and symmetrical in itself, while the
others are asymmetrical. ‘The femur has a strong third tro-
chanter; the fibula is complete; the astragalus more Rhino-
cerotic than Equine. There is no trace of a hallux, but the

THE TAPIRIDZA, 8311

fifth digit of the pes appears to be represented by an osseous
rudiment,

In the presence of the full complement of incisors and
canines the Tapir is more Horse-like than Rhinocerotic, but is
still very peculiar ; for the outer upper incisors are larger than
the canines, while the outer lower incisors are much smaller
than the canines, and are apt to fall out at a certain age. The
canines, are still more closely approximated to the incisors
than in the Horse, especially in the lower jaw, and, conse-
quently, the diastema is very large. The six posterior molars
in the upper jaw, and the five posterior molars in the lower,
present nearly the same structure. There is a low outer wall
with two slightly-marked concavities (in the maxillary teeth)
or convexities (in the mandibular teeth) on its outer face.
From this two ridge-like laminz run inward and a little back-
ward across the crown of the tooth. The valleys are broad
and shallow, and the coat of cement very thin. The molar
tooth of the Tapir thus represents the plan of structure com-
mon to the Perissodactyle in its simplest form. Deepen the
valleys, increase the curvature of the wall and lamine, give
the Jatter a more directly backward slope; cause them to de-
velop accessory ridges and pillars, and increase the quantity
of cement; and the upper molar of the Tapir will gradually
pass through the structure of that of the Rhinoceros to that
of the Horse.

In the anterior upper premolar (or milk-molar?) the an-
terior moiety of the crown is incompletely developed. In the
anterior lower premolar the anterior basal process, which ex-
_ists in all the molars, is excessively developed, so that the
crown of the tooth assumes the bicrescentic pattern of the
Rhinoceros’s lower grinder. This probably indicates the man-
ner in which the Tapiroid form of inferior molar is converted
into the Rhinocerotic, or Equine, form.

The stomach is simple and oval, the cardiac and pyloric
orifices being closely approximated. The czecum is proportion-
ally smaller than in the Horse or Rhinoceros. There is no
gall-bladder. The heart is devoid of a septal bone and of a
Eustachian valve. There is only a single vena cava anterior,
and the aorta divides into an anterior and a posterior trunk,
There is no third bronchus. No distinct scrotum is present.
There are vesicule seminales and prostatic glands, but no
Cowper’s glands. The placentation is diffuse. The teats are
two, and inguinal.

There are two or three species of Tapir at present living

312 THE ANATOMY OF VERTEBRATED ANIMALS.

in South America and one in Southwest China, Malacca, and
Sumatra. The genus Zapirus has been found fossil in Europe
in rocks of miocene age. The closely-allied extinct genera
Lophiodon (and Coryphodon?) carry the Tapiride back
through the eocene epoch.

d. The Palewotheride.—These are all extinct animals, the
remains of which are found in the older tertiary rocks; and
which are closely allied, on the one hand, with the Horses and,
on the other, with the Tapirs.

The type of the family, Palcwotheridium, resembles the
Tapir in most respects, but has only three digits in the manus
as well as in the pes. The dental formula, however, is
i. 5. = p.m. —m.~- The diastema is smaller than in the
Tapir, and the patterns of the grinding teeth of both jaws
are more like those of the Rhinoceros.

e. The Macrauchenide.—The genus Macrauchenia is also
an extinct form, which occurs in later tertiary or quaternary
deposits in South America.

The feet are tridactyle, and the dental formula is
t. 55 Gi p.m = m.3-; The teeth are disposed in a nearly
continuous series. The crowns of the incisors present a deep
fossa, as in the Hquide. The molars are in part Equine, in
part Rhinocerotic in character. The skull is, on the whole,
Equine, but the nasal bones are very short and Tapiroid. The
vertebrz of the long neck are extraordinarily similar to those
of the Camelide, and especially of the Llamas.

2. The Artiodactyla.—The number of the dorso-lumbar
vertebrze in this group is always fewer than twenty-two, and
rarely exceeds nineteen.

The third digit of each foot is asymmetrical in itself, and
usually forms a symmetrical pair with the fourth digit; and
the functional toes of the hind-foot are even in number—that
is to say, either two or four.

The femur is devoid of any third trochanter; the facets
upon the distal face of the astragalus are subequal, that for
the cuboid being nearly as large as that for the navicular
bone. The tympanic is large, and the pterygoid process of
the sphenoid is not perforated.

The posterior premolar teeth usually differ a good deal
from the succeeding molars, being simpler in pattern. The
last milk-molar in the lower jaw is trilobed; but this is also
the case in some Perissodactyla

THE SUID. 313

The stomach is more or less complex. The czecum, though
well developed, is smaller than in the Perissodactyla.

The mammez are inguinal or abdominal. When horns are
present, they are double, supported, wholly or partly, by the
frontal bone and provided with an osseous core, which is
almost always an outgrowth from that bone.

The Artiodactyla are divisible into the Von-Ruminantiu
and the Ruminantia.

A. The Von-Ruminantia usually have more than one pair
of incisors in the upper jaw. The molar teeth have either a
mammillate, a transversely-ridged, or a rhinocerotic pattern.
In only one genus, Dicotyles, are any of the metacarpal or
metatarsal bones anchylosed together. They are devoid of
horns, and the stomach has rarely more than two divisions.

The Non-Ruminantia are divisible into three families:
The Suide, the Hippopotamide, and the Anoplotheride ; but
more or fewer of the members of this last group may have
ruminated.

a. The Suidc have the skin of moderate thickness and
hairy ; the limbs slender, and the third and fourth toes con-
siderably longer than the second and fifth. The teats are
abdominal, and there is a scrotum. The dental formula varies
considerably, but the molars have a multituberculate or trans-
versely-ridged grinding surface.

In the genus Sus, the dental formula is ¢. $5 ¢ j=; p.m.
4-4 :
tm

By way of contrast with the Horse, I add some more de-
tailed statements regarding the anatomy of the Pig as a com-
mon and very good example of an Artiodactyle. The Pig has
seven cervical vertebra, nineteen* dorso-lumbar, of which
fourteen are dorsal, four sacral, and twenty to twenty-three
caudal. The atlas has wide oblique ale, as in the Horse.
The centra of the other cervical vertebrae are short, with
nearly flat articular surfaces, and this flatness is retained in
the dorso-lumbar region. The cervical and dorsal vertebre are
provided with long spines, that of the first dorsal vertebra
being the longest of all. Up to the twelfth dorsal the spines
all slope backward; beyond it they slope forward, if at all.

In the ninth dorsal vertebra the postzygapophysis presents
an articular surface on its dorsal side, and the prezygapophysis
of the tenth vertebra bends round so as to overlap this surface.
This character is continued in the succeeding vertebre as far

* Exceptionally, the number may be increased to twenty-two.

14

314 THE ANATOMY OF VERTEBRATED ANIMALS.

as the first sacral. The transverse processes of the penulti-
mate and last lumbar vertebrz are tolerably long, but they are
inclined forward as well as outward, and do not articulate
with one another, or with the first sacral. |

In the skull the supraoccipital is inclined upward and for-
ward into a great transverse crest, to which the parietals con-
tribute but little. The parietals are early anchylosed. The
temporal ridges remain widely separated in the middle of the
roof of the skull.

The frontal bone has a post-orbital process, and so has the
jugal, but the two do not meet so as to bound the orbit. The
lachrymal is very large, and its two canals open on the face.
The nasals are very long, and the premaxillz unite with them
for a great distance. There is a przenasal bone, or ossification
of the cartilaginous septum of the nose. The bony palate ex-
tends back beyond the level of the last molar. The base of
the external pterygoid process is not perforated. The surface
for the articulation of the lower jaw is transversely elongated,
convex from before backward, and bounded behind and inter-
nally by a post-glenoidal ridge.

The tympanic bulla is very large, and the exceedingly long
bony meatus curves upward and outward, between the squamo-
sal and the mastoid, with both of which it is anchylosed, to
the root of the zygoma, where its aperture looks almost directly
upward, The post-tympanic is closely appressed to the post-
elenoidal process, so as, with the latter, to encircle the meatus,
The proper mastoid is distinct, though short, but there is a
very long paramastoid developed from the exoccipital and ex-
tending behind and below the mastoid.

The rami of the mandible are completely anchylosed at the
symphysis. There is a long perpendicular portion of the
ramus. ‘The condyle is transversely elongated and convex,
antero-posteriorly ; the coronoid process ascends hardly higher
than it. In a longitudinal section, the cavity of the cerebral
hemispheres is more rounded than in the Horse, and lies
above, as well as in front of, that for the cerebellum.

The scapula is long and narrow. It is devoid of acromion,
and has but a small coracoid process.

The radius and ulna are complete, but are anchylosed to-
gether in the prone position. The distal end of the ulna
articulates with the cuneiform bone.

The carpus contains eight bones, but the radial bone in
the distal series may be either the trapezium, or a rudiment
of the pollex. The lunare and the axis of the third metacarpal

THE OSTEOLOGY OF THE PIG. 315

have the same relation as in the Horse. The third and fourth
digits are larger than the other two, and form a symmetrical
pair. There are sesamoid bones on the ventral face of the
articulations between the. metacarpal and the basal phalanx,
and of that between the middle and the distal phalanges.
Each distal phalanx is incased in a small hoof. The femur
has a round ligament. There is no third trochanter. The
fibula is complete, and its distal end articulates with the cal-
caneum. There are the usual seven tarsal bones. The tibial
end of the astragalus has the form of a deeply-grooved pulley,
the direction of the groove corresponding nearly with the
length of the foot. The distal end presents a convex sub-
cylindrical surface divided by a ridge into two facets, of
which one is somewhat less than the other, and articulates
with the cuboid.

The metatarsus and phalanges of the pes are disposed like
the corresponding bones in the manus.

The fore-part of the body is supported upon the anterior
extremities by a muscular sling composed of the serratus, leva-
tor anguli scapule, and sternoscapularis, much as in the Horse,
with which the Pig exhibits a general correspondence in its
myology. ‘The muscles which move the digits, however, have
undergone less modification. Hach digit of the manus, for
example, has its proper extensors, and there is an extensor ossis
metacarpt pollicis which ends on the basal phalanx of the
second digit. A pronator teres is inserted into the lower half
of the radius. The flexor perforatus has only two tendons,
which go to the third and fourth digits. The flexor perforans
sends two large tendons to the third and fourth, and two small
ones to the second and fifth digits. There is a large interos-
seus muscle on the radial side of the third digit, and another
on the ulnar side of the fourth ; but the interossez of the inter-
space between these digits are represented only by fibrous
tissue. The second and fifth digits have each two interossei.
There is no soleus. The strong and fleshy plantaris arises
from the outer condyle, beneath the gastrocnemius ; and, en-
closed between the two heads of the latter, passes to the
inner side of the tendo Achillis ; its tendon curves round this
tendon, passes over the end of the calcaneum as over a pulley,
enters the sole, and finally divides into the two perforated
tendons of the third and fourth digits. The inner and outer
digits of the pes, like those of the manus, have no perforated
tendons.

A large and fleshy flexor hailucis longus arises from the

316 THE ANATOMY OF VERTEBRATED ANIMALS.

fibula and the interosseous ligament, and its broad tendon
passes into the sole and coalesces with the tendon of the
smaller flexor longus digitorum. ‘The conjoined tendons divide
into four slips—two large, median, and two small, inner and
outer. These go to the distal phalanges and sesamoids of the
respective digits.

The tibialis posticus is absent, but there is a small tibialis
anticus.

A very complicated muscle represents the extensor longus
digitorum and the peroncus tertius. It arises by (a) a strong
round tendon from the outer condyle of the femur, just in front
of the external lateral ligament. From this tendon proceed
two fleshy bellies, one of which supplies tendons to the third,
fourth, and fifth digits, while the other ends in a broad band
of tendinous fibres, which is inserted into the third metatarsal
and the ectocuneiform. Into this band is inserted (6) the
second fleshy head which arises from the upper part of the
tibia; and it is traversed by the tendon of (c) the third head,
which is slender, arises from the fibula, and sends its long and
delicate tendon to the dorsum of the second digit.

The peroncus longus is present, and its tendon is inserted
into the entocuneiform and the second metatarsal. There is
no peronceus brevis. A peronceus 4ti et d5ti digiti arises from
the upper part of the fibula, behind the peronceus longus, and
ends in a tendon which passes behind, and on the inner side
of, that of the latter muscle, to the dorsum of the foot, where
it divides into two branches which join the extensor sheaths
of the fourth and fifth digits,

The extensor brevis goes to the two middle digits, and is
connected with the middle tendon of the extensor longus.

The interossez are similar to those of the manus,

The formula of the milk dentition of the Pig (which is com-
plete at the third month after birth) is di. 24 de. dm. F3-

The outer upper incisors are directed obliquely outward
and backward. In the upper jaw, the anterior two molars
present sharp longitudinal edges, while the posterior two
have broad crowns with two transverse ridges. In the man-
dible the anterior three molars have sharp longitudinal edges,
while the hindermost has a broad, three-ridged crown,

The first permanent molar is the first tooth of the per-
manent set which comes into place (at about six months after
birth), and the permanent dentition is completed in the third

THE DENTITION OF THE PIG. — 317

year, at which time the first deciduous molar, which is not
replaced, falls out. Hence the formula of the permanent denti-
tion is 7.33 ¢& 5 p.m. a3 mM. = 40.

The permanent incisors in the upper jaw have short, broad,
vertically-disposed crowns, and lie in a longitudinal series, the
external being separated by an interval from the others. The
elongated inferior incisors lie side by side, are greatly inclined
forward and upward, and are grooved upon their upper or
inner faces. The strong, angulated crowns of the canines are
bent upward and outward in both jaws. They work against
one another, in such a manner that the upper wears on its
anterior and external face, the lower on the posterior aspect
of its apex. The crowns of the premolars are all brought to a
cutting longitudinal edge, while the molars have broad crowns
with transverse ridges subdivided into tubercles. Of these
ridges there are two in the anterior two molars of each jaw,
while the posterior molar is more complex, having at fewest
three distinct ridges. The molar teeth all develop roots; but
the canines continue to grow for so long a time, in the Boar,
that they might be said to be rootless.

The alimentary canal is ten or twelve times as long as the
body.

The stomach is less simple in structure than it appears to
be at first sight. The cardiac end presents a small czecum, in
which is a spiral fold of the mucous membrane; and, at the
entrance of the cesophagus, the epithelial lining is folded so
as to form a sort of valve. Folds of the mucous membrane,
between which there lies a groove, extend from the cardia
toward the pylorus, and foreshadow the more developed struct-
ure observable in Ruminants.

The cecum has not above one-sixth the capacity of the
stomach, and the ilium projects into it, so as to form a very
efficient ilioceecal valve. The liver is provided with a gall-
bladder. The heart is devoid of a Eustachian valve, and
sometimes, but not always, possesses a septal ossification.

There is only one anterior cava. The aorta gives off an in-
nominata, whence the right subclavian and the two carotids
arise, and a left subclavian. This is an arrangement midway
between that observed in the Horse and that in Man.

The trachea, before it divides, gives off a third bronchus,
which passes to the right lung; and the lungs are deeply lobed.

In the brain the cerebral hemispheres rise above the cere
bellum much more than they do in the Horse.

318 THE ANATOMY OF VERTEBRATED ANIMALS,

In the male, the penis is contained in a long prepuce, and,
like that of the Horse, is devoid of a bone and provided with
retractor muscles. The prostate is lobed. There is a large
uterus masculinus and well-developed vesicule: seminales.
The ducts of Cowper’s glands open into a cecal cavity con-
tained in the muscular bulb. The testes descend into a scro-
tum. In the Sow, a pair of Gaertner’s canals, or persistent
Wolffian ducts, open into the vestibule beside the urinary
meatus. ‘The uterine cornua are very long, and the ovaries
are lobulated. The period of gestation is sixteen to twenty
weeks. The ovum, at first spherical, retains that form until it
attains a diameter of nearly half an inch. It then rapidly
elongates into a coiled filiform body, as much as twenty inches
long. Both the allantois and the umbilical vesicle at the same
time assume a spindle-shape.

The allantois soon becomes divided into an internal epithe-
lial and an external vascular layer ; the latter becoming united
with the chorion, through the extremities of which the allan-
tois eventually passes. The villi are very numerous, minute,
and spread over the whole surface of the ovum.

The Suide exhibit great variations in their dentition and
in the structure of the stomach.

In Porcus (the Babyrussa) the dental formula is ¢. $5 ¢ i

BB.

;-,; the canines are enormously elongated and recurved,

p.mM.

and the pharynx is provided with peculiar air-sacs.

The stomach is divided into three chambers, and the groove
leading from the cesophagus toward the pylorus is more dis-
tinctly marked than in the Sus.

In Dicotyles (the Peccaries) the upper incisors are also
reduced to two on each side, and the molar teeth present
transverse ridges, which are more distinct and less tuberculated
than in Sus.

The stomach is divided into three sacs, and is provided
with an cesophageal groove as in the preceding genus.

The middle metatarsals and metacarpals coalesce into a
cannon-bone, and the fifth digit of the pes is represented only
by its metatarsal.

In Phacocherus (the Wart-hog) the upper incisors are
reduced to one pair, and the hindermost molars, which are the
only ones which are not shed in the old animal, are of great
size, and possess a complicated, tuberculated structure.

The Suide# are represented by one genus or another in al}

THE HIPPOPOTAMID A. 319

the great distributional provinces except the Australian* and
Novo-Zelanian. Porcus is peculiar to part of the Malay Ar-
chipelago, Dicotyles to South America, and Phacocheerus to
South Africa.

A great variety of swine-like Ungulata existed during the
deposition of the older tertiary strata, and are the earliest
known members of the group.

b. The Hippopotamide are represented at present only by
the genera Hippopotamus and Cheropus. These animals
have a huge head, a heavy body, covered with a thick integu-
ment, provided with scanty hairs, and short, stout, tetradactyle
limbs, all the four toes of which rest on the ground. The
female has inguinal teats, and the male is devoid of a scrotum.

The dental formula of the adult Hippopotamus is 4. >=
e: a p.m. = m. ==, while Cheropus has only two incisors in
the lower jaw. The tubercles of the molar teeth, when ground
down by mastication, present a double trefoil pattern, and the
hindermost inferior molar is trilobed. The incisors are straight
and tusk-like. The very large and curved canines are directed
downward in the upper jaw, upward in the lower. Their mu-
tual attrition wears the anterior face of the extremity of the
upper, and the posterior face of that of the lower, flat.

The milk dentition consist of dz. = d.c. s d.m. — The

last lower deciduous molar is trilobed, and the first deciduous
molar persists a long time, and seems not to be replaced.

The stomach is divided into three or four compartments,
and there is no cecum, ‘The liver has a gall-bladder, and the
kidneys are lobulated.

The skeleton is very pig-like, but in some respects ap-
proaches the Ruminants. The centra are slightly convex in
front, and concave behind, in the cervical region, but not else-
where. The prezygapophyses overlap the postzygapophyses
in the posterior dorso-lumbar vetebrae. On the other hand, the
transverse processes of the last lumbar vertebre articulate
with those of the preceding and succeeding vertebra, as in
the Horse and other Perissodactyles.

In the skull the orbits are nearly complete posteriorly, and
they become almost tubular by the outward production of the
frontal and lachrymal bones.

The nasals and premaxille unite for a great extent. The

* The Papuan pig may have been introduced from the westward.

320 THE ANATOMY OF VERTEBRATED ANIMALS.

osseous palate is long; the large tympanic bone is anchylosed
with the approximated post-glenoidal and post-tympanic pro-
cesses.

The mandible is extremely massive, and has a backwardly
produced angle.

The scapula has a short acromion, The radius and ulna
are complete and anchylosed, and there are eight bones in the
carpus. The fibula is complete, and the tarsus, which has
seven bones, much resembles that of the Pig.

The Hippopotamide are at present confined to Africa;
but a species abounded in the rivers of Europe in the later
tertiary times.

Merycopotamus of the miocene Fauna of the Sewalik
Hills appears to have been a Hippopotamid, with upper molars
having a quadri-crescentic, ruminant-like pattern, and lower
molars bi-crescentic and rhinocerotic in character.

In the Suide and Hippopotamide, it is interesting to
remark the tendency to the coalescence of the metacarpals
and metatarsals in Dicotyles ; the disappearance of the upper
incisors by pairs in Dicotyles, Porcus, and Phacocherus ; and
the great complexity of the stomach in Dicotyles and Hippo-
potamus ; as they are so many approximations toward the
structure of the Ruminant Artiodactyla. And the transition
from the non-Ruminant to the Ruminant groups, or rather the
common stem of both, is furnished by the Anoplotheride.

ce. The family of the Anoplotheride exclusively contains
extinct Mammals belonging to the eocene and miocene epochs.
They are most conspicuously distinguished by the circumstance
that the teeth, of which there are eleven on each side, above
and below, in the adult dentition, are not interrupted by any
gap in front of and behind the canine, as they are in the pre-
ceding genera, but form an uninterrupted and even series, as
in Man.

The dental formula of the adult Anoplotherium is i. =;
c. 1 p.m. —, mM. 55) supposing that the first premolar is really
such, and not a persistent milk-molar.

The upper and lower molars have the general structure of
those of the Rhinoceros; but the laminze of the upper are bent
more backward into parallelism with the outer wall, and a
strong conical pillar is developed on the inner side of the
anterior lamina. The skull resembles that of the Ruminant
Zragulide in structure, but the orbit is incomplete behind

THE ANOPLOTHERIDA. 321

The rest of the skeleton partly resembles that of the Pigs,
and partly that of the Ruminants.* .

In Xiphodon and Cainotherium, which are ordinarily com-
prised among the Anoplotheride (though, in all probability,
they are true Ruminants of the Traguline group), the orbit is

Fia. 101.—The skeleton of an Ox (Bos).

*In Anoplotherium secundauium the digit 7%. is developed in each foot,
though not nearly so long as #., which is neariy symmetrical in itself. There
is an approach to the same structure in the manus of Cainotherium.

322 THE ANATOMY OF VERTEBRATED ANIMAIS.

complete, and both upper and lower molars put on the Rumi-
nant characteristics. In dentition, Cainotherium differs from
a Ruminant only in possessing all the upper incisors, while
no existing adult Ruminant has more than the outer upper
incisors. Weare of course unacquainted with the structure
of the stomach in these animals, but they so closely resemble
Ruminant Artiodactyla that it is highly probable they may
have possessed the faculty of rumination in a more or less per-
fect degree.

B. The Auminantia.—In the commonly-recognized mem-
bers of this division of the Artiodactyla there is never more
than one pair of incisors, and that the outermost, in the upper
jaw of the adult. Canines may or may not exist in the upper
jaw; they are always present in the lower jaw, and are gen-
erally inclined forward and closely approximated to the inci-
sors, which they usually resemble in form. It consequently
happens that they are often reckoned as incisors, and Rumi-
nants are said to possess eight cutting teeth in the lower jaw.

With one exception (Hycemoschus), the metacarpal and
metatarsal bones of the third and fourth digits early become
anchylosed together into a single, so-called cannon-bone.
There isa peculiar bone called madlleolar, which takes the
place of the distal end of the fibula, articulating below with
the caleaneum and above with the astragalus.

The great majority of the Ruminantia possess horns, the
bony supports, or cores, of which are developed on each side
of tke middle line; and, except in the Giraffe, are outgrowths
of the frontal bones.

The stomach has, at fewest, theee divisions; and, in the
majority of the Auminantia, it has four compartments.

If the stomach of a typical Ruminant, such as a Sheep or
an Ox, be examined, it will be found to be divisible into two
principal moieties, the one cardiac and the other pyloric, while
each of these is again subdivided into two others. Thus the
extreme cardiac end of the cardiac moiety is dilated into an
enormous sac of irregular form, the mucous membrane of
which is raised up into a vast number of close-set papille.
This chamber is the Rumen, or Paunch. It communicates,
by a wide aperture, with a much smaller chamber, which con-
stitutes the second subdivision of the cardiac moiety. Thisis
called the Reticulum, or Honeycomb stomach, from the fact
that its mucous membrane is raised up intoa great number of
folds, which cross one another at right angles, and, in this
way, enclose a multitude of hexagonal-sided cells. The reticu:

THE RUMINANT STOMACH. 323

lum communicates by a narrow aperture with the first sub-
division of the pyloric moiety, which is somewhat more elon-
gated in form. The mucous membrane of this subdivision is
produced into a vast number of longitudinal folds of various
heights, but the majority of them are sufficiently large to ex-

A,

=

®

WW
Nn)

Y
—Y

Fig. 102.—A, the stomach of a Sheep. B, that of a Musk-deer (Zragulus). ., esophagus;
Rn., rumen; et., reticulum; Ps., psalterium; A., Ad, abomasum; Dw., duo-
denum; /y., pylorus

tend almost completely across the cavity of the chamber;
they thus reduce that cavity to a series of narrow radiating
clefts interposed between the lamella. When this portion of
the stomach is slit open, longitudinally, the lamellze fall apart
like the leaves of a book, whence it has received the fanciful
name of the Psalterium from anatomists, while butchers give
it that of Manyplies. The fourth segment of the stomach, or
second subdivision of the pyloric moiety, is termed the Ado:

B24 THE ANATOMY OF VERTEBRATED ANIMALS.

masum, or Rennet stomach, This portion is comparatively
slender and elongated, and its mucous membrane has a totally
different character from that of the other three segments, being
soft, highly vascular, and glandular, and raised into only a few
longitudinal ridges.

Jt will be observed that the psalterium is so constructed as
to play the part of a very efficient strainer between the reticu-
lum and the abomasum; nothing but very finely-divided, or
semi-fluid matter, being capable of traversing the interstices
of its lamellee.

The gastric aperture of the cesophagus is situated at the
junction of the paunch and the reticulum ; the margins of its
opening are raised into muscular folds, and are produced,
parallel with one another, along the roof of the reticulum to
the opening which leads into the psaltertum. When the lips
of this groove are approximated together, a canal is formed,
which conducts directly from the cesophagus to the psalte-
rium.

A Ruminant, when feeding, crops the grass rapidly and
ereedily, seizing it with its tongue and biting off the bundle
of blades thus collected, by pressing the lower incisors against
the callous pad formed by the gum which covers the pre-
maxilla. The bunches of grass are then hastily swallowed,
accompanied by abundant saliva. After grazing until its ap-
petite is satisfied, the Ruminant lies down, usually inclining
the body to one side, and remains quiescent for a certain space
of time. A sudden movement of the flanks is then observed,
very similar to that which might be produced by a hiccough ;
and careful watching of the long neck will show that some-
thing is, at the same time, quickly forced up the gullet into
the cavity of the mouth. This is a bolus of grass, which has
been sodden in the fluids contained in the stomach, and is re-
turned, saturated with them, to be masticated. In an ordinary
Ruminant this operation of mastication is always performed in
the same way. ‘The lower jaw makes a first stroke, say in the
direction from left to right, while the second stroke, and all
those which follow it until the bolus is sufficiently masticated,
take place from right to left, or in the opposite direction to
that of the first. While the mastication is going on, fresh
quantities of saliva are poured into the mouth, and, when the
crass is thoroughly ground up, the semifluid product is passed
back into the pharynx and swallowed once more. These
actions are repeated until the greater portion of the grass
which has been cropped is pulpified.

THE ACT OF RUMINATION. 325

The precise nature of the operation, the external features
of which have now been described, has been the subject of
much investigation and discussion. The following points appear
to have been clearly established :

1. Rumination is altogether prevented by paralysis of the
abdominal muscles, and it is a good deal impeded by any in-
terference with the free action of the diaphragm.

2. Neither the paunch, nor the reticulum, ever becomes
eompletely emptied by the process of regurgitation. The
paunch is found half full of sodden fodder, even in animals
which have perished by starvation.

3. When solid substances are swallowed, they pass indif-
ferently into the rumen, or reticulum, and are constantly driven
backward and forward, from the one into the other, by peris-
taltic actions of the walls of the stomach.

4, Fluids may pass either into the paunch and the re-
ticulum ; or into the psalterium, and thence at once into the
fourth stomach, according to circumstances.

5. Rumination is perfectly well effected after the lips of
the cesophageal groove have been closely united by wire
sutures.

It would appear, therefore, that the cropped grass passes
into the reticulum and rumen, andis macerated inthem. But
there is no reason to believe that the reticulum takes any
special share in modelling the boluses which have to be re-
turned into the mouth. More probably, a sudden and simul-
taneous contraction of the diaphragm and of the abdominal
muscles compresses the contents of the rumen and reticulum,
and drives the sodden fodder against the cardiac aperture of
the stomach. This opens, and then the cardiac end of the
cesophagus, becoming passively dilated, receives as much of the
fodder as it will contain. The cardiac aperture now becoming
closed, the bolus, thus shut off, is propelled, by the reversed
peristaltic action of the muscular walls of the cesophagus, into
the mouth, where it undergoes the thorough mastication which
has been described.

The sodden fodder is prevented from passing out of the
psalterial aperture of the reticulum, in part by the narrowness
of that aperture, and in part by the fine grating formed by the
edges of the psalterial laminz. But when the semifluid
matter, returned after mastication, once more reaches the
cardia, it is compelled to pass toward the psalterial end of the
reticulum (even apart from the guidance afforded by the lips
of the cesophageal groove) on account of the direction of the

326 THE ANATOMY OF VERTEBRATED ANIMALS.

cesophagus and the bounding of the cardiac aperture, on the
side of the rumen, by a raised ridge. ‘The chewed matter thus
flowing over the surface of the more solid contents of the re-
ticulum reaches the psalterium; and, in consequence of the fine
state of division of its solids, readily traverses the interspaces
of the lamelle of that organ, and passes into the fourth
stomach, there to be submitted to the action of the gastric
juice and to undergo the digestion of the protein compounds,
which have remained unaffected by the previous mastication
and insalivation.

The Ruminantia are divided into three groups: 4a. the
Tragulide, 6, the Cotylophora, and ¢. the Camelide.

a. The Tragulide are a remarkable family, formerly united
with the genus Moschus, and still commonly known under the
name of Musk Deer, though they are devoid of the musk-sac
and, in other respects, are totally different from Moschus.
They are at present restricted to Southern Asia and Africa ;
and they are particularly interesting, as affording, in many
respects, a connecting link between the typical Ruminants and
the other Artiodactyla, especially the Anoplotheride. Thus,
the second and fifth digits are complete in both fore- and hind-
feet, and the metacarpals and metatarsals of the third and
fourth digits unite very late, or, as in one genus, Hycemoschus,
not at all. The canines are well developed in both jaws, and
the premolar teeth are sharp and cutting.

The cesophagus opens at the junction of the rumen with
the reticulum, the communication between the two being very
wide (Fig. 102 B). The epithelium of the rumen is papillate,
and there are two cesophageal folds, as in ordinary Ruminants,
but the psalterium is represented only by a very short and
narrow tube, the lining membrane of which is devoid of folds.

The surface of the hemispheres of the brain has fewer
convolutions than in any other Ruminants, though this may
very possibly be connected with the small size of the animal;
as it is a general rule that, within the same group, the brain is
less convoluted in small than in large animals.

The blood-corpuscles, small in all Ruminantia, are remark-
ably minute in the Zragulide, not exceeding 75495 Of an inch
in diameter. They have circular contours,

The placenta is very nearly diffuse, the foetal villi being
scattered over the chorion in bands, not collected into cotyle-
dons.

As further remarkable peculiarities of this group may be
mentioned the anchylosis of the malleolar bone with the tibia,

aisha

at Mrinal m+

ir oa ee oor

2 Oa Da ti nan

a a eo Pe See

THE COTYLOPHORA. 327

and the tendency to ossification in the pelvic ligaments and
of the aponeurosis of the muscles of the back, in adult males,
Finally, the navicular, cuboid, and ectocuneiform bones in the
tarsus are all anchylosed together. If, as is probable, Xipho-
don is one of the Zragulide, the group has existed since the
eocene epoch.

b. The Cotylophora are, like the preceding group, unguli-
grade, but the outer metacarpals and metatarsals are incom-
plete at their proximal ends, and the middle ones are early
anchylosed into a cannon-bone. The malleolar bone is always
distinct. The navicular and the cuboid bones of the tarsus are
anchylosed together, but rarely with any other tarsal bone.
The premaxilla is devoid of teeth in the adult, The stomach
has the structure which has been described as typical.

The blood-corpuscles are circular, and may have a diameter
of as little as 3454 of an inch.

The foetal villi are gathered together into bunches or co-
tyledons, which may present either a convex or a concave face
toward the uterus. They are received into persistent eleva-
tions of the mucous membrane of the uterus, the surfaces of
which present a reverse curvature.

All the Cotylophora except Moschus, the true Musk Deer,
are provided with horns, but these horns are of two kinds.
The bony core, in the one case, is ensheathed in a strong horny
epidermic case; while, in the other, the epidermis of the integ-
ument which covers the core does not become so modified.
In the former kind of horn, the core becomes excavated by the
extension into it of the frontal sinuses, whence the Ruminants
which possess such horns are not unfrequently called Cavi-
cornia (Antelopes, Sheep, Goats, Oxen). As a general rule,
the horny sheath persists throughout life, growing with the
growth of the core. But in the remarkable Prong-horned
Antelope of North America (Antilocapra), the horny sheath
is annually shed and replaced by a newly-formed one.

Of the second kind of horn, or that which acquires no horny
sheath, there are also two kinds. In the Giraffe, the horn-
cores are attached over the coronal suture, at the junction of
the frontal and parietal bones, with which they are not anchy-
iosed; they persist throughout life, and are always covered
by a soft and hairy integument.

In the Deer, on the other hand, the frontal bones grow out
into solid processes, which are, at first, covered by soft and
hairy integument; generally they are developed in the male
sex only, but both sexes have them in the Reindeer. The

328 THE ANATOMY OF VERTEBRATED ANIMALS.

horns attain their full size very rapidly, and then a circular
ridge, which makes its appearance at a short distance from the
root of the horn and is called the “ burr,” divides the horn into
the “ pedicel” on the skull-side of the burr, and the “ beam”
on the opposite side. The circulation in the vessels of the beam
now gradually languishes, its integument dies and peels off, and
the dead bony substance beneath is exposed. Absorption and
sloughing next occur at the extremity of the pedicel, just as
might happen in any other case of necrosis. The beam and
burr are shed, and the end of the pedicel scabbing over, fresh
integument gradually grows up under the scab, and eventually
restores to the extremity of the pedicel its pristine smooth and
hairy covering.

The rapidity with which the development of bony matter
into Deer-horn takes place is wonderful, horns weighing sey-
enty-two lbs. having been produced in ten weeks.

The Cotylophora are represented in all parts of the world
except the Australian and Novo-Zelanian provinces. They
have not yet been traced back farther than the miocene epoch.

c. The Camelide or (Tylopoda) are devoid of horns; and,
unlike the other Ruminants, they walk upon the palmar and
plantar surfaces of the phalanges of the third and fourth toes,
which are alone developed. Broad integumentary cushions
form a sole to the foot; while the nails are flattened and can
hardly be called hoofs.

The arches of the cervical vertebrz, and not their trans-
verse processes, are perforated by the canal of the vertebral
artery; a character which the camels share with the Macrau-
chenide.

The metacarpals are separated by a deep cleft, and the
distal phalanges of the digits are nearly symmetrical in them-
selves, The distal facets of the astragalus are more unequal
than in the other Auminantia, and the navicular and cuboid
bones are not anchylosed together.

The premaxille have 4 single strong outer incisor on each
side. Large curved and pointed canines are developed in each
jaw, and are quite distinct from the series of the incisors in
the mandible. There are not more than five grinding teeth in
a continuous series above and below.

The stomach is unlike that of the typical Ruminants. The
cesophagus opens directly into the paunch, which is lined by a
smooth, not papillose, epithelial coat. From its walls, at
least two sets of diverticula, with comparatively narrow
mouths, are developed. These, the so-called “ater-cells,”

——~. oe

THE TOXODONTIA. 329

serve to strain off from the contents of the paunch, and to
retain in store, a considerable quantity of water. ‘lhe reticu-
lum is sharply defined from the rumen, and communicates with
it by a comparatively small aperture. ‘The cesophageal groove
is bounded by only one ridge, which lies upon its left side,
The psalterium is reduced to a mere tubular passage, without
lamin; and the abomasum is large, and has the ordinary
structure. The pyloric end of the duodenum is considerably
dilated, and has been taken for a division of the stomach. The
cecum is short and simple. By a remarkable exception
among the Mammalia, the red blood-corpuscles are elliptical,
The foetal villi are scattered evenly over the chorion, so that
the placenta is diffuse.

While the Zragulide connect the typical Ruminants with
the non-ruminant Artiodactyles, the Camelide, on the other
hand, link them with Macrauchenia and the Perissodactyles,

The Camelide are at present represented by two very
distinct groups—the Camels of the Old World and the Llamas
of the New. They occur in the fossil state as far back as the
miocene epoch.

If. The Toxopont14.—This order has been founded for the
reception of the large extinct Mammal (Zoxodon), remains
of which have been discovered in the later tertiary deposits
of South America.

The supraoccipital surface of the massive skull slopes
obliquely upward and forward. There are supraorbital pro-
longations. ‘The zygomata are very strong and arched, and
the bony palate is very long.

In the upper jaw there are two small, inner, and two large,
outer, incisors. In the lower jaw there are six incisors. In
the mandible there are canines in the middle of the interval
between the incisors and the grinders. In the upper jaw of
the adult, only indications of the former existence of alveoli
for canines remain. The grinding teeth are seven on each side
above, and six on each side below. They are greatly bowed
(whence the name of the genus), so as to be convex outward
and concave inward. They grow from persistent pulps, and
the enamel is absent upon their inner faces.

The centra of the cervical vertebree have flattened articular
faces. The dorso-lumbar vertebrae and the sacrum are not
known. ‘The ribs are spongy internal'y, like those of ordinary
Mammals, not compact, as in the Sirenia.

The scapula has a very large supraspinous fossa, as ip

530 THE ANATOMY OF VERTEBRATED ANIMALS.

Tapirus. There is no acromion, and the coronoid is very
small, The humerus and the ulna are very massive, but the
rest of the fore-limb is unknown. The femur is devoid of any
third trochanter, and, like the tibia and astragalus, presents a
good many points of resemblance to the corresponding bone
in the Elephants. ;

It is a curious comment upon the pretension to reconstruct
animals from mere fragments of their bones and teeth which
some have put forward, that, although we know the skull, the
dentition, and the most important of the limb-bones of Zoxo-
don, no one ventures to predict the characters of its feet, still
less to say any thing about its internal organization. Hven its
zoological affinities are extremely doubtful, and it is hard to
say whether Zoxodon is merely an aberrant Ungulate, or
whether it is the type of a new order.

III. The Strenra.—As has been already said, nothing is
known of the placentation of this small but important group
of Mammalia, all the existing forms of which are aquatic in
their habits, frequenting great rivers and their estuaries; and
are devoid of hind-limbs, while the integument of the caudal
end of the body is produced into a flattened horizontal fin.
No dorsal fin is ever present. ‘The demarcation between the
head and neck is but obscurely marked, and the fore-limbs are
converted into paddles, upon which only rudimentary nails are
developed. Scanty bristles cover the surface of the body.
The snout is fleshy and tumid, and the valvular nostrils, which
are perfectly distinct from one another, are situated consider-
ably above its termination. There is a well-developed third
eyelid, the pinna of the ear is absent, and the mamme are
thoracic ; a circumstance which has probably not a little con-
tributed to the origination of the myths respecting the exist-
ence of mermaids.

The Sirenia were formerly united with the Whales and
Porpoises as Cetacea herbivora. But their organization dif-
fers from that of the true Cetaceans in almost every particular,
while they are closely allied with the Ungulata.

The cervical vertebrae are reduced to six in one genus-——
Manatus. The bodies of these vertebrae are always com-
pressed from before backward, but they are never all an-
chylosed together (it is rare for any of them to be thus
united), and the second has a distinct odontoid process. The
dorsal vertebree have broad and depressed spines, and may be
as many as seventeen or eighteen in number, while there are

THE SIRENIA. 331

not more than three lumbar vertebrae; and the hindermost of
these even is probably to be regarded as sacral. There are
twenty or more caudal vertebre, the terminal ones being not
polygonal, but depressed, with well-developed processes.

The zygapophyses of successive vertebre articulate to-
gether in the dorsal region; but, in the lumbar and caudal re-
gions, the postzygapophyses disappear and the prezygapo-
physes are small, and neither overlap, nor embrace, the spine
of the antecedent vertebra. The posterior moiety of the spine
thus acquires considerable flexibility. There is no true sacrum,
the vertebra called “sacral” being only determined as such
by its connection with the rudimentary pelvis. Strong sub-
vertebral chevron-bones are placed beneath the interarticular
cartilages of the caudal vertebra. The heads of the ribs
articulate with the centra of all the vertebra. The bodies of
the ribs are very thick, rounded, and have a remarkably dense
and laminated structure. The narrow and elongated sternum
is an undivided mass of bone, and is connected by ossified
sternal ribs with the anterior three pairs of vertebral ribs.

In the skull the elongated and subcylindrical form of the
cranial cavity is worthy of notice, as it strongly contrasts with
the form of the brain-case in the Cetacea. The supraoccipital
is very large and slopes upward and forward a long way on to
the upper surface of the skull; but it does not separate the
parietal bones; which, as usual, unite in the sagittal suture.
The frontals are prolonged into broad supraorbital processes.
The nasal bones are abortive, and, in the dry skull, the external
nares are very wide, and look upward. The tympanic bone is
a thick hoop, anchylosed with the periotic bones, and readily
comes away from the skull with them. The zygoma is
enormously stout. The premaxille constitute a large portion
of the boundary of the gape; and the lower jaw has a high
ascending portion, with a large coronoid process.

The scapula has a distinct spine occupying the ordinary
position. There are no clavicles. The humerus has its distal
end fashioned into articular surfaces, upon which the radius
and ulna are freely movable. The pollex is rudimentary, and
the other digits have no more than three phalanges each.

The pelvis is rudimentary, the bones which represent the
ossa innominata being connected by their proximal ends with
the transverse processes of the last of the precaudal vertebre.
They are disposed vertically to the axis of the body. No
trace of the hind-limbs has been observed in any of the exist
ng Sirenia.

332 THE ANATOMY OF VERTEBRATED ANIMALS.

The premaxillary region of the palate, and the correspond-
ing surface of the mandible, are coated with mammillated and
rugose horny plates formed of hardened epithelium; and, in
the extinct genus hytina, these plates were the only masti-
cating organs, as there were no teeth. In H/alicore (the
Dugong’), there are teeth which have no vertical successors,
form no roots, and are devoid of enamel; while, in Alanatus,
there are milk-molars, and the grinding teeth are enamelled,
and present crowns with double transverse ridges.

The adult Manatee has no incisors. In the Dugong there
are no incisors In the mandible of the adult. The male has
two tusk-like incisors which project from their sockets in the
premaxille ; while, in the femaie, the tusks remain concealed
in their alveoli.

In the foetal state, both Halicore and Manatus have in-
cisors in the mandible as well as in the premaxiliz.

The stomach is divided into two portions by a median con-
striction, and its cardiac end is provided with a peculiar gland.
Its plyoric end, in some species, gives off two czeca.

Fic. 103.—Dorsal view of the heart ofa Dugong (alicore), its cavities being laid open.—R.
®., right ventricle; Z. v., left ventricle. V. c¢. 8. 8., left superior vena caya. V.c. 8. d.,
right superior vena cava. V.c.7%., vena cavainferior. /. o. v., the inner end of a cecal
diverticulum of the right auricle, into which a style is introduced, and which represents
the foramen ovale. O, the auricular septum.

There is a caecum at the junction of the large and small in-
testine. Salivary glands are well developed. The apical pore
tion of the septum ventriculorum is deeply cleft, so that the
ventricles are separated from one another through about half
their extent.

There are two superior cave and a Eustachian valve. Ex:

THE CETACEA. 333

tensive arterial and venous retia mirabilia are developed in
Manatus. In consequence of the great length of the thoracic
region and the brevity of the sternum, the diaphragm takes a
very unusual course, extending very obliquely from before
backward, and causing the upper part of the thoracic cavity to
extend posteriorly over almost the whole of the abdomen.
The greatly-elongated lungs fill this part of the thoracic cham-
ber, while the broad heart lies in its anterior and sternal portion.

The arytenoid cartilages are not prolonged as in the Ceta-
cea. A broad and high epiglottis is capable of covering the
glottis completely.

There is no third bronchus.

The cutaneous muscle is largely inserted into the humerus,
and the sub-caudal muscles extend forward as far as the pos-
terior lumbar vertebree. The chief muscles of the antibrachium
and manus are present.

The male Sirenia possess vesicule seminales. The uterus
is two-horned.

There are two living genera of Sirenia—the Dugong
(Halicore), which is found upon the shores of the Indian
Ocean and of Australia; and the Manatee (Manatus), which
is confined to the South American and African borders of the
Atlantic.

A third genus, Rhytina, which had a coriaceous integu-
ment almost devoid of hair, and possessed no teeth, abounded
in Behring’s Straits less than a century ago. It is now alto-
gether extinct.

The Miocene genus, Halitherium, appears to have pos-
sessed distinct, though small, hind-limbs.

IV. The Creracea.—In this order of Mammalia the form
of the body is still more fish-like than in the Sirenia. There
is no trace of a neck, the contour of the head passing gradu-
ally into that of the body. A horizontally-flattened caudal
fin is always present; and, very generally, the dorsal integu-
ment is produced into a median, laterally-compressed dorsal
fin. The body is incased in a thick smooth integument, be-
neath which a very thick layer of fat is deposited. Hairs are
almost entirely absent in the adult state.

As in the recent Sirenia, the anterior limbs alone are
present. Externally they do not present any indication of
division into brachium, antibrachium, and manus, but have the
form of a broad, flattened paddle, without any vestiges of nails.

The one or two apertures by which the cavity of the nose

334 THE ANATOMY OF VERTEBRATED ANIMALS,

opens externally, are always situated at the top of the head,
and far removed from the extremity of the snout. There is
no third eyelid, and the very small auditory apertures are to-
tally devoid of any pinna. The teats are two, and, in the
female, are lodged in depressions on each side of the vulva.

The articular surfaces of the centra of the vertebrz are
flat, and the epiphyses usually remain distinct for a long time,

The spinal column, as a whole, is remarkable for the short-
ness of its cervical, and the length of its lumbar region, there
being sometimes a greater number of lumbar than of dorsal
vertebrae. There is no sacrum. The caudal vertebre are only
distinguishable from the posterior lumbo-sacral vertebrae by
their chevron-bones. The second vertebra of the neck is de-
void of any odontoid process; and it very commonly happens
that more or fewer of the cervical vertebrae, the bodies of
which are often so short as to be mere disks, are anchylosed
together, either by their arches, or by their centra, or by both.
The centra of all the succeeding vertebree are large in propor-
tion to their arches, and the inter-vertebral fibro-cartilages are
exceedingly thick, so as to confer great flexibility and elasti-
city on the spine. The arches of the hinder dorsal vertebra,
and of those of the lumbar and caudal regions, are not articu-

lated together by zygapophyses. The centra of the posterior
caudal vertebrze lose their processes and become polygonal.

Very few of the ribs become connected with the sternum
at their distal ends; and, in contradistinction to what happens
in most Mammalia, the proximal ends of the majority of the
ribs are connected only with the transverse processes of the
vertebree, and not with their bodies.

The skull is even more remarkably modified than the ver-
tebral column. ‘The brain-case itself has a spheroidal form ;
while the jaws are greatly prolonged, the principal enlarge-
ment of the upper jaw taking place in the region which lies in
front of the nasal aperture. The basis cranii, as a whole, is
ramarkably broad, and its upper surface concave from before
backward, the sella turcica being very slightly indicated,
The parietal bones are comparatively small, and do not meet
in a sagittal suture, as they do in other Mammalia, the
supraoccipital, with an interparietal bone, being interposed be-
tween them, and extending forward so as to unite with the
frontals. Each frontal bone is produced outward into a great
bony plate which covers the orbit. The squamosal bone sends
a very large and stout zygomatic process forward to meet this
supra-orbital prolongation of the frontal. The proper jugal

+>"

went

THE CETACEA. 335

bone, on the other hand, which bounds the orbit below, is ex-
ceedingly slender. The very large maxilla extends backward
and outward in contact with the frontal, or even overlapping
the greater part of its surface; and it stretches forward to
very near the anterior end of the snout, so that almost the
whole of the gape is bounded by the maxilla.

The premaxillz, on the other hand, though very long, inas-
much as they occupy the whole length of the jaw in the mid-
dle line, from the anterior nasal aperture to the end of the
snout, are almost entirely excluded from the gape.

The nasal bones are always short; and, sometimes, are
mere bony tuberosities united with the frontal bones behind
the anterior nasal aperture. The turbinal bones are almost
always rudimentary, and the nasal passages are nearly verti-
cal, in consequence, for the most part, of the rudimentary con-
dition and shortness of the nasal bones.

The periotic bones are loosely connected with the squa-
mosal and tympanic, and are usually united with the other
bones of the skull only by cartilage, so that they fall out very
readily in the dry skull. The tympanic bones are commonly
of very considerable size, thick and scroll-shaped.

The lower jaw has hardly any coronoid process, and its
ramus has no perpendicular portion, the condyle being situated
upon its posterior extremity. The body of the hyoid isa very
broad plate of bone, and has two pair of stout, well-ossified
cornua.

The Cetacea are devoid of clavicles. If the spine of the
scapula is present, it is a low ridge situated close to the ante-
rior edge of the bone; but it commonly terminates in a long
acromion process, and, sometimes, there is a conspicuous,
straight, and flattened coracoid. The humerus is short, and
the articular surfaces at its distal end are, in allrecent Cetacea,
flat facets inclined to one another at an angle. The ulna and
the radius are short, laterally-compressed bones, without any
movement upon one another; and, in all recent Cetacea, they
are not freely movable upon the humerus. The carpus is often
imperfectly ossified. When the carpal bones are complete,
they are polygonal and imbedded in a fibrous tissue; not
united by articulations provided with synovial membranes.
The digits do not exceed five in number, but there are always
more than three phalanges in some of them.

The pelvis is represented by two bones which lie parallel
with the axis of the vertebral column, give attachment to the
corpora cavernosa in the male, and, therefore, probably yepre-

336 THE ANATOMY OF VERTEBRATED ANIMALS.

sent the ischia. They are elongated, convex upward and con-
cave downward, and are connected with the vertebral column
only by fibrous tissue. In some few Cetacea (Balenoidea)
ossicles, which lie on the outer side of the peivic bone, appear
to represent the femur, but no further indication of a hind-
limb has been discovered.

In most of the Cetacea, the muscles which, in other Mam-
malia, move the antibrachium and the manus, are absent, -
those which move the humerus upon the shoulder-blade being,
alone, represented,

In no recent Cetacean have the teeth any vertical suc-
cessors, nor more than a single root. The alveoli are often
incompletely separated from one another. The number of the
teeth varies very greatly, but they are almost always nearly
uniform in character. ‘There appear to be no salivary glands.
The stomach is’ complicated, being divided into, at fewest,
three chambers, of which the first is a kind of paunch lined by
a thick epithelium, while the second and the third are more
elongated, the last stomach being that in which digestion
takes place.

The arteries and veins form great plexuses, or retia mt-
rabilia, and these are especially conspicuous in the cavity of
the thorax, upon each side of the vertebral column, and in the
intercostal spaces.

The soft palate is remarkably long and muscular. The
epiglottis and the arytenoid cartilages are more or less pro-
duced, so as to give the glottis the shape of a funnel, the apex
of which is embraced by the soft palate, in such a manner as
to form a continuous air-passage from the posterior nares to
the larynx, on each side of which the food passes. The very
short trachea, before it divides into the bronchi, gives off the
so-called “ third bronchus ” to the right lung, as in the Bears,
Walruses, and Ruminants.

The kidneys are deeply subdivided into lobules. In the
male the testes always remain in the abdomen, and there are
no vesiculz seminales. The penis is devoid of a bone. The
uterus of the female is deeply divided into two horns, and the
villi of the foetus are scattered over its chorion, as in other
inammals with a diffuse placentation.

The Cetacea are divisible into three groups: the Bale-
noidea, the Delphinoidea, and the Phocodontia.*

* For further information respecting the characters of the recent Cetacea, I
refer the reader to Prof, Flowers’s very valuable memoir ‘‘On the Osteology

of Inia and Fontoporia,” published in the “Transactions of the Zoological
Society for 1867.”

:) Shean ae

THE BALANOIDEA. 337

a. In the Balenoidea the nasal chambers communicate
with the exterior by two apertures, which are capable of being
shut at the will of the animal, and are called spiracles. These
are not connected with any saccular dilatations of the nasal
passages, situated between the skull and the integument.

In the spinal column, no rib has a complete neck and capi-
tulum, the heads of even the most anterior ribs being united

mm r
ant TM Muni
ny oe

IVTEAURYNTRUPAUEDNUERNVCESN CNLUAULCOLLCNUAERILE

\

fe. 104.—Lateral and superior views of the skull of a fetal Whale (Balena A ustralia).—
The jugal bones are absent, and the figure does not sufficiently indicate the outward
curvature of the ramus of the mandible (Jf.).

15

338 THE ANATOMY OF VERTEBRATED ANIMALS.

with the bodies of the vertebra only by ligament. The chief
connection of all ‘the ribs, therefore, and the only connection
of most of them, is with the transverse processes of the verte-
bree. The short and broad sternum unites only with the first
rib, and the union is direct, so that there are no sternocostal
ribs.

5 rm hy A

be ue ;
het Poy) C20

uA os eu ih

Fre. 105.—“ Ear-bones ” of the adult Balena Australis—Seen from within in the upper
figure; from without in the lower. #w., Eustachian canal; Aw., external auditory
meatus; Sty., ossified root of the styloid process.

The skull (Fig. 104) is exceedingly large in proportion to
the body, and nearly symmetrical, The nasal bones, WVa.,
though short, are longer, and more like those of ordinary
mammals, than is the case in other Cetacea. The maxilla,
BE extends outward in front of the great supraorbital process
of the frontal, /7., but it does not cover the frontal bane,

There is a distinct lachrymal. Each ramus of the mandible, —

Mn., is convex outward and concave inward; and the space
between the rami of the mandible is very much greater than
the width of the maxillo-premaxillary part of the skull, which
tapers to its anterior end, and is more or less convex upward

THE BALANOIDEA. 339

and concave inferiorly. The two rami of the mandible are
connected only by ligament at the symphysis.

Minute teeth are developed in foetal Balenide, but are
very soon lost, and their place taken by the so-called Whale-
bone, or Baleen plates. Hach of these is triangular, with a
thick, smooth outer edge, somewhat concave from above down-
ward, which, in the natural position of the plates, is nearly
vertical, and is covered by the great lower lip. The upper
edge of the plate, also slightly concave, is attached to a trans-
verse elevation of the gum covering the palate. Vascular
papillae extend from this ridge into cavities of corresponding
dimensions, which lie, parallel with one another, in the baleen
plate. The third side of the triangular baleen plate, somewhat
convex and sloping from the middle line above, downward and
outward, gives origin to a number of filamentous processes,
into which the baleen appears to be, as it were, frayed out.
When the mouth is shut, these frayed edges of the numerous
and close-set baleen plates, which are longest in the middle
of each series, and shortest at each end, enclose a cavity, the
bottom of which is occupied by the large and fleshy tongue.
By raising the tongue, whatever solid matters are enclosed in
the mouth can be forced back into the pharynx and swallowed ;
while the water in which they were suspended is driven out
between the baleen plates. The Whale feeds by putting this
gigantic strainer into operation, as it swims through the shoals
of minute molluscs, crustaceans, and fishes, which are con-
stantly found at the surface of the sea. Opening its capacious
mouth, and allowing the sea-water, with its multitudinous
tenants, to fill the oral cavity, the Whale shuts the lower jaw
upon the baleen plates, and, straining out the water through
them, swallows the prey stranded upon its vast tongue.

In some of the #Salwnoidea, e. g., Balena rostrata, the
cricoid cartilage and the rings of the trachea are incomplete
in front, and a large air-sac is developed in the cricothyroid
space. The Balenoidea possess olfactory nerves and a dis-
tinct, though small, olfactory apparatus. The sclerotic coat
of the eyeball is enormously thick, and the optic nerve is sur-
rounded by a rete-mirabile. The tympanic membrane is con-
nected with the malleus by ligament. The semicircular canals
are very small, but the cochlea is large, and makes only 13
turns. The muscles of the antibrachium and manus are not
altogether absent.

The right Whale (Balena), and the Fin-fishes (Mega:
ptera, Balenoptera, etc.), belong to this division.

340 THE ANATOMY OF VERTEBRATED ANIMALS.

b. In the Delphinoidea the nasal chambers open by only
a single spiracle on the top of the head; and saccular dilata-
tions of various dimensions are developed from the walls of the
passage which connects this aperture with the bony naso-
palatine passages, and lie between the integument and the
outer surface of the skull.

More or fewer of the anterior ribs have heads and necks,
the capitula articulating with the bodies of the vertebra, as
in other Mammalia. The elongated sternum is, almost al-
ways, composed of several pieces arranged in a longitudinal
series; and cartilaginous, or ossified, sternal ribs are present
in greater or smaller number. The nasal bones, which are
very short, and have their upper surfaces tubercle-like, are
more or less asymmetrically developed, as are also the max-
ill; so that the facial part of the skull appears distorted.
The maxillze are expanded behind, and cover the orbital pro-
cess of the frontal bone wholly or partially. The lachrymal
bone is usually small and confluent with the slender jugal, but
it may be large and distinct. The rami of the mandible are
not arcuated outward, and they become united in a longer or
shorter symphysis. The mandible, as a whole, is not sensibly
broader than the corresponding portion of the maxillo-premax-
illary part of the skull.

Teeth always exist after birth, and are never replaced by |
baleen plates. They are usually numerous, but sometimes few
and deciduous. Occasionally, only one or two teeth persist,
and these, as in the Narwhal, may take the form of immense-
ly-elongated tusks.

To this division belong the Physeteride Platanistide and
Delphinide.

The Physeteride possess functional teeth only in the low-
er jaw. ‘The asymmetry of the skull is strongly pronounced ;
and, in the adult, the maxillary and frontal bones are pro-
duced, so as to form a sort of basin upon the upper and ante-
rior surface of the skull, The pterygoids meet in the middle
line below, and the mandibular symphysis is sometimes ex-
tremely long.

The greater number of the cervical vertebrae are anchy-
losed. The hinder ribs lose their tubercular, but retain their
capitular articulation with the vertebra. The costal carti-
lages are not ossified. The pectoral limbs are small, and a
dorsal fin is usually present.

The proper Sperm Whales (Physeferince) have an enor-
mous head, with a quadrate truncated snout, at the anterior

AA Seer ea
c

THE DELPHINOIDEA. 341

superior angle of which the spiracle is placed. The teeth
become fully developed only in the lower jaw. The cranial
basin is immense, and is filled by a loose connective tissue, in
which the peculiar fat known as spermaceti is contained. Am-
bergris is a sort of bezoar, found in the alimentary canal of the
Cachalot, and seemingly derived from the fatty matter con-

(C)

fic. 106.—Upper (A), under (B), and lateral (C) views of the skull of a feetal Cachalot
(Physeter).—The nasal hones are not represented in the upper view, and the hinder ead
of the jugal is displaced from its natural connection with the squamosal in ((),

B42 THE ANATOMY OF VERTEBRATED ANIMALS.

tained in the Cephalopoda on which the Cetacean feeds. In
the other group of the Physeteride—the Ziphiine or Rhyn-
choceti—to which the Bottlenosed Whale (Z/yperoodon) be-
longs, there are only one or two pairs of fully-formed teeth in
the mandible. Some recent and many fossil (middle and later
tertiary) genera of the Cetaceans are remarkable for the elon-
gated rostrum formed by the solid ossification and anchylosis
of the ethmoid, premaxillz, and maxille.

The Platanistide are fluviatile or estuarine Cetacea,
which occur in the Ganges and in the rivers of South America.
The cervical vertebrae are not anchylosed, and the costal car-
tilages are not ossified. The tubercula and capitula of the
ribs blend together posteriorly. The symphysis of the man-
dibles is extremely long and the jaws are narrow. Numerous
teeth with compressed fangs are found in both jaws. The
eyes are small, and in Patanista they are rudimentary.

In the Dephinide lastly (Dolphins, Porpoises, Gram-
puses), the teeth are usually numerous in both jaws, though
the Narwhal is an exception to this rule, as has already been
mentioned.

The anterior cervical vertebre are generally anchylosed
together. The posterior ribs lose their capitula and become
articulated only with the transverse processes of the vertebrae.
The costal cartilages are well ossified. ‘The symphysis of the
mandible does not exceed one third of the rami in length, and
the frontal and maxillary bones are not especially produced
upward at their edges.

As the common Porpoise (Phocena communis), which is
a member of this group, is the Cetacean which is most likely
to come within reach of the student, it may be useful to
speak at some length of its more interesting anatomical pe-
culiarities.

The adult animal is usually about five feet long, and is
covered with a smooth integument upon which no hair is to
be discovered, though a few hairs are visible about the mouth
in the young animal. The contour of the anterior part of the
head is very convex, and presents, in the middle line, the
spiracle or blow-hole, which has the form of a crescent with
the points turned downward and forward. The eyes are small
and placed low down, close to the posterior end of the gape
of the mouth, which is bounded by dense and rigid lips. The
aperture of the ear lies about an inch and three-quarters be:
hind the eye, and is so minute as to be discovered with diffi-
culty. The genital aperture is placed a long way in front of

THE SKELETON OF THE PORPOISE. 843

the anus in the male; while, in the female, the interval, in
which the fossze which lodge the teats are situated, is much
less. There is a conspicuous vertical dorsal fin in addition to
the flattened caudal fin. Immediately beneath the skin isa
thick layer of blubber, as in other Cetacea.

In the spongy texture of all the bones, the absence of me-
dullary cavities in those of the limbs, and in the long per-
sistent separability of the epiphyses of the centra of the verte-
bree, the Porpoise resembles other Cetacea ; as it does in the
shortness of the cervical, and the length of the lumbar, region
of the spinal column. .

The seven cervical vertebrve are all anchylosed together, and
the atlas, which is very large in proportion to the rest, over-
laps them above and at the sides. The centra of the hinder
cervicals are so short and broad that they are mere plates of
bone. There are twenty-eight dorso-lumbar vertebree, of which
fifteen are dorsal. In all but the most anterior of these
vertebrae, the zygapophyses are abortive ; and long accessory
processes, developed from the front-part of the neural arches,
loosely embrace the spine of the vertebrae in front. This ar-
rangement, together with the thickness of the intervertebral
ligaments, gives great flexibility to the spinal column. The
transverse processes of the hinder dorsal, and of the lumbar,
vertebree are very long. There are five pairs of true ribs. The
sternebrz anchylose into an elongated sternum. ‘The anterior
caudal vertebrz are provided with large chevron-bones, and
their transverse processes exhibit notches through which
branches of the aorta pass.

In consequence of the globular form of the brain-case, and
the prolongation of the jaws, the skull has a flask-like shape.
There is a slight want of symmetry about the base of the upper
jaw, but it is hardly appreciable.

In a longitudinal section, the flatness and the upwardly
concave contour of the base of the skull; the extreme shallow-
ness of the sella turcica ; the presence of an ossified tentorium 3
and the broad imperforate anterior wall, in the place of the
cribriform plate of the ethmoid, are striking features. The
synchondrosis between the basi- and presphenoid is persistent.
On the base of the skull the basi-occipital gives off great pro-
cesses outward and downward, to form, together with a para-
mastoid prolongation of the exoccipital, and the squamosal, a
chamber in which the anchylosed tympanic and periotic bones
are contained. ‘The ex- and supra-occipitals, together with the
interparietals, form the whole back wall and middle of the

344 THE ANATOMY OF VERTEBRATED ANIMALS.

roof of the cranium, separating the parietals completely, and
the frontals largely, and reaching the nasal bones.

The basi-sphenoid is anchylosed with the small and almost
horizontal alisphenoids, and there are no sphenoidal pterygoid
processes. The parictals are small, and occupy only the under
and lateral portions of the brain-case. The frontal bones are
very broad and expanded, and are completely anchylosed to-
gether, where they form the front wall of the brain-case. Pos-
teriorly and above, they diverge to receive the interparictal.
The supra-orbital processes are extremely large, and are
directed forward and outward, not backward and outward, as
in the Whalebone Whales. The greater part of the superior
surface of the frontals and of their orbital processes is rough
and covered over by the expanded maxillary bones, which
allow only a narrow, transverse, smooth, band-like surface,
formed by the frontals, to be seen on the upper and anterior
region of the skull. The rough surface is marked by two
shallow grooves which pass from below upward, and are con-
vex toward one another and to the middle line. Correspond-
ing grooves exist on the under side of the expanded proximal
ends of the maxillaries; and, when these are in their natural
positions, the coadapted grooves form two canals, which are
blind in front and above. These, in the natural state, are full
of air, and communicate with the air-chambers at the base of
the skull and with the Eustachian tubes.

The narrow premaxillze are anchylosed with the inner
margins of the maxillz, and contribute only a very small por-
tion of the alveolar margin of the upper jaw. The alveoli are
not completely separated from one another. The pterygoid
bones do not unite in the palate. They have a peculiar ex-
cavated form, and are notched for the passage of the ends of
the Eustachian tubes into the nasal passages. These are nearly
vertical and are separated by the large and strong vomer.
Their superior apertures are left quite uncovered in conse-
quence of the small size, tubercular form, and backward posi-
tion of the nasal bones. The squamosal is relatively small, but
has the characteristically cetacean, large, zygomatic process 3
this extends forward nearly to the posterior end of the supra-
orbital process, and gives attachment to the slender jugal.

The periotic bones form a dense osseous mass, which is
anchylosed with the no less heavy and thick, scroll-shaped
tympanic. The pars mastoidea of the periotic mass fits pretty
accurately into a recess of the chamber which has already been
described ; and is thus held in position in the dry skull, though
it is very easily detached.

THE SKELETON OF THE PORPOISE. 345

When the fympano-periotig bone and all the facial bones
are removed, only two pair of foramina are visible in the base
of the skull, The anterior pair give exit to the second, third,
fourth, the anterior division of the fifth and the sixth nerves,
and these answer to the optic and sphenorbital foramina. The
posterior pair take the place of the oval, posterior lacerated,
and jugular foramina, and the precondyloid foramina open into
them posteriorly. The rami of the mandibles are only united
by a short symphysis. The body of the hyoid is broad and
hexagonal, and has two slender, anterior, and two broad and
flat, posterior, cornua.

In the natural position the fore-limbs stand out from the
body with their flat surfaces looking upward and downward;
the upper surface being directed a little backward, and the
lower a little forward. The tuberosity of the short humerus
is directed forward. The carpus contains six or seven ossifica-
tions. The number of phalanges in the digits is two, eight,
six, three, two, counting the pollex as the first.

The pelvic bones are elongated, slightly curved, osseous
styles. They lie with their long axes parallel to the vertebral
column, their convex sides upward, and their smaller ends for-
ward, within an inch of the centra of the vertebra, their
hinder-ends being close to the third chevron-bone of the tail.
The front-ends are about an inch apart. Behind its centre,
each bone presents a flattened thickening for the attachment
of the corpus cavernosum of its side.

The cutaneous muscle is very largely developed, and lies
between two layers of blubber, the thick surperficial one sepa-
rating it from the skin, and the thin deep layer from the subja-
cent muscles. It may be said to be disposed in two broad
layers, a dorsal and a ventral, on each side; these extend from
the occipital crest, and from the rami of the mandibles, to the
tail. Both these divisions send off strong bundles to the hu-
merus, which act as powerful adductors, abductors, protractors,
and retractors of the fin. There is no trapezius, and the rep-
resentative of the latissimus dorsi is very small. A strong
occipito-humeralis, from the paramastoid to the tuberosity of
the humerus, seems to represent the cleido-mastoid and clavicu-
lar deltoid. A costo-humeralis extends from the sternum to the
inner tuberosity of the humerus. A small coraco-brachialis ex-
tends from the apex of the coracoid to the inner tuberosity of the
humerus. The pectoralis major seems to be represented by a
muscle which arises from the sternum, close to the attachment of
the third and fourth ribs, and is inserted into the ulna, The tre

346 THE ANATOMY OF VERTEBRATED ANIMALS.

ceps extensor is represented by tendinous fibres in which muscle
cannot always be detected, which extend from the posterior face
of the humerus to the ulna. The other muscles of the forearm
and all those of the manus are absent. The dorsal muscles
form a thick continuous mass from the end of the tail to the
occiput ; and, on the ventral side of the spinal column, the
subcaudal muscles are similarly continued forward, as far as
the middle of the thorax. An ischio-caudalis passes, on each
side, from the anterior chevron-bones to the ischium. Between
their attachments is an aponeurosis which supports the anus;
ischio-cavernous muscles pass from the ischia to the corpora
cavernosa.

The diaphragm has no tendinous centre. Its pillars are
very thin, and, extending between the kidneys and the spine,
become tendinous, and are attached to the ventral faces of the
vertebrae, as far as the ninth lumbar. A strong fibrous apo-
neurosis is continued back over the subvertebral muscles to the
pelvic bones. Between these bones and the ends of the trans-
verse processes of the twenty-eighth and twenty-ninth verte-
bree (counting from the first dorsal) the aponeurosis is so stout
as to form an almost distinct fibrous band, which occupies the
place of an ilium. Theureter lies between the ischio-vertebral
fascia and the peritonzeum.

The teeth are small and numerous, and their crowns are
obtuse and constricted. The passage of the pharynx is di-
vided in the middle, the soft palate being prolonged into a mus-
cular funnel, the opening of which closely fits the constricted
neck of the long cone into which the epiglottis and the aryte-
noid cartilages are produced. ‘Thus the arrangement which is
transitory in the Marsupial is permanent in the Cetacean.

The stomach is divided into three sacs. ‘The first is large,
conical, and lined by a coarse white epithelial coat. The gul-
let opens directly into it. The second stomach communicates
with the first by an aperture which is close to the cardiac end
of the gullet, and is surrounded by a very prominent rugose
lip. A curved passage about one inch long and capable of
admitting the finger, lined by a white epithelium similar to
that of the first, leads into the second stomach. The second
stomach is lined by an extremely vascular and soft mucous
membrane, with about ten strong longitudinal folds, separated
by deep sulci, interrupted by transverse ridges. A narrow
and curved canal leads from this into the third stomach, which
has a tubular form and is bent upon itself. Its lining mem-
brane is quite smooth, A small, circular, pyloric aperture

THE HEART OF THE PORPOISE. 347

places this in communication with the dilated commencement
of the duodenum, which has sometimes been regarded asa
fourth stomach. Its lining membrane presents longitudinal
rugze continuous with those of the duodenum itself. The con-
joined pancreatic and biliary ducts open just beyond the di-
lated part of the duodenum. ‘There is no coecum, or demar-
cation between the large and small intestines. ‘The bilobed
liver has no gall-bladder.

In the heart the fossa ovalis is distinct, but there is neither
Eustachian nor Thebesian valve. The vena cava inferior is
long and wide, but is not especially dilated near the heart.
Muscular fibres are not continued on to it from the diaphragm,
The aorta and pulmonary arteries are not dilated at their ori-
gins. The arteries have a great tendency to break up into
plexuses. Thus the internal carotids form great net-works
which communicate with vertebral plexuses, extending through-
out the entire spinal canal. The brachial artery divides into
two branches, and these subdivide into innumerable parallel
twigs. The intercostal arteries are the chief source of the
large thoracic plexuses, which lie at the sides of the vertebral
column in the dorsal half of the thorax. Finally, an arterial
rete mirabile surrounds the caudal aorta. The veins form
plexuses corresponding to, and mixed up with, those of the
arteries ; and a very large venous plexus lies on the subverte-
bral muscles in the abdomen and thorax.

The respiratory apparatus of the Porpoise presents many
remarkable peculiarities. The contour of the front part of the
head, as bounded by the integument, is very convex—the cor-
responding facial region of the skull, on the contrary, is very
concave. The interval between the two is occupied, in part,
by fibrous and fatty tissue; and, in part, by a singularly sac- *
culated spiracular chamber, which connects the single spiracle
with the double external nares of the skull. Two valves, an
anterior and a posterior, lie immediately above these external
nares and close the communication between them and the
chamber, except at such times as it is forced open from below.
Hach nasal passage remains distinct from the other as far as
the valves, the middle of each of the latter being fastened to
the septum, so that there may be said to be a pair of valves
for each opening between the passages and the spiracular
chamber. Each nasal passage, after it ceases to be surrounded
by bone, sends off two diverticula, one forward and one back-
ward, The anterior, which lies between the anterior valve
and the premaxilla, is a simple sac, lined with a thin, black,

¥

348 THE ANATOMY OF VERTEBRATED ANIMALS.

smooth membrane. The posterior diverticulum lies between
the posterior valve and the ethmoid and nasal bones. It is
incompletely divided by a sort of shelf, is prolonged forward,
‘round, and in front of, the anterior valve, and ends blindly in
the middle line above the anterior sac. The spiracular chamber
itself is produced, on each side, into a large lateral sac, the
walls of which are raised in strong parallel ridges, and covered
with a black papillose integument. The walls of these sacs
are strong and elastic. Layers of muscular fibres pass from
the occipital ridge to the posterior lip of the spiracle, and
from the edges of the maxillz to its anterior lip. Their ac-
tion is necessarily to open the spiracle and compress the sacs.
There is no sphincter, the form of the spiracle causing it to be
naturally shut by the fitting together of its walls, and the
pressure of the water upon them.

When a Porpoise comes to the surface to “blow,” the
shape of the posterior, concave lip of the crescentic spiracle
does not sensibly alter; but the anterior, convex lip is pulled
downward and forward, its surface becoming somewhat de-
pressed, and its free edge nearly straight—so that the aperture,
when fully dilated, assumes the form of a half-moon. At the
same time, the air is expelled with a rushing sound. The
inspiratory act must be very rapid, as the spiracle remains
open for only a very short time aiter expiration ends. When
the larger Cetacea come up to breathe, the expired vapor
suddenly condenses into a cloud; and, if expiration commences
before the spiracle is actually at the surface, a certain quantity
of spray may be driven up along with the violent current of
the expelled air. This gives rise to the appearance termed
the “ spouting” of Whales, which does not arise, as it is
commonly said to do, from the straining off of the sea-water
swallowed with the food, and its expulsion by the nostrils.

The epiglottis, in front, and the arytenoid cartilages be-
hind, are prolonged into a tapering tube, dilated at its summit
into a knob. The muscular soft palate embraces the neck of
this knob so closely that it cannot be withdrawn without
considerable effort. And thus, during life, the nasal air-
passages and the glottis are kept perfectly continuous; while
the Porpoise dashes through the water, open-mouthed, after
its prey. The point at which the extra bronchus to the right
lung is given off is separated by four rings from the bifurcation
of the trachea. The lungs are not lobed and their tissue is
very dense and elastic.

The cerebral hemispheres are, taken together, broader than

THE PHOCODONTIA. 349

they are long. In the upper view they leave not more than a
seventh of the length of the cerebellum exposed, while they
overlap it largely at the sides. The outer surface of the hemi-
spheres is extremely convoluted, the gyri being numerous and
separated by deep sulci. There is a well-marked Sylvian
fissure, with a central lobe, or insula. A rudiment of a pos-
terior cornu has been observed, in the lateral ventricle. The
corpus callosum is small, relatively to the size of the hemi-
spheres, and the anterior commissure is almost obsolete. The
medulla oblongata has corpora trapezoidea. ‘The olfactory
nerves are wanting—a circumstance which agrees with the
entire absence of ethmoidal turbinals. The eye has a thick
sclerotic, and there is a choanoid muscle; no nictitating mem-
brane is present.

The external auditory aperture is so small as to be easily
overlooked. The meatus auditorius is a narrow undulating
tube about two inches long. The tympanic membrane is con-
cave externally; and, as is usual in the Cetacea, is connected
by a ligament with the handle of the malleus. There is only
a small aperture in the stapes. The tensor tympani arises, as
in Carnivores, from a fossa in the periotic ossification.

The Eustachian tube passes through the notch in the ptery-
goid and opens into the nasal passage on the inner side of that
notch, Close to its commencement it communicates, by an
oval aperture, with a remarkable air-chamber, which extends
backward between the periotic mass and the bass cranii, and
forward to the under side of the expanded part of the maxilla,
where it opens into the canal between the maxilla and the
frontal already described. These chambers, like the bronchi,
are generally full of nematoid worms. The testes and penis
of the male are enormous in proportion to the size of the
body.

The penis is devoid of a bone, and, ordinarily, is bent up
in the long preputial sheath.

ce. The Phocodontia are represented only by Zeuglodon,
Squalodon, and other large extinct cetaceans of the tertiary
epoch. These remarkable fossil forms constitute connecting
links between the Cetacea and the aquatic Carnivora. The
cervical vertebree are distinct and unanchylosed, nearly re-
sembling those of the Rhyncoceti. The caudal vertebrae have
their transverse processes perforated vertically, as in many
Cetacea. The distal ends of the ribs are enlarged somewhat
as in the Sirenia. The skull is symmetrical, and the nasal
bones, though still short, are longer than those of any other

3850 THE ANATOMY OF VERTEBRATED ANIMALS.

cetacean. The zygomatic processes of the squamosal are large
and thick, and the supraorbital processes of the frontals wide
and expanded as in the Cetacea.

The scapula appears to have had a spine and acromion like
that of Manatus. The humerus is,compressed from the side,
and has true articular surfaces upon its distal end, although
they are of small size.

The molar teeth have laterally-compressed crowns with
serrated edges and two fangs, resembling tiose of many seals,
and Zeuglodon differs from all the other Cetacea in the circum-
stance that some of its teeth have vertical successors.

The DecipuaTE Mammatia.—These may be subdivided,
according to the form of the placenta, into two groups: the
Zonaria and the Discoidea. In the former the placenta sur-
rounds the chorion like a hoop, leaving its ends free of villi, or
nearly so,

In the Discoidea, on the other hand, the placenta takes
the form of a thick disk, which is sometimes more or less lobed.

The mammalia which possess a zonary placentation are the
Carnivora, the Proboscidea, and the Hyracoidea.

Kach of these divisions is very closely related to one of the
foregoing. ‘Thus the Carnivora approach the Cetacea; the
Proboscidea, the Sirenia ; and the Myracoidea, the Ungu-
lata.

The Zonarta. 1. The Carnivora.—In this order the
head, relatively to the body, is of moderate or small size; and
hair is abundant.

The cervical vertebree are free and unanchylosed, and their
centra are elongated. ‘The odontoid process of the second is
welldeveloped. The dorso-lumbar vertebree are almost always
twenty in number, rarely twenty-one or nineteen. ‘The num-
ber of dorsal and lumbar vertebrae, respectively, varies be-
tween sixteen dorsal and four lumbar, and thirteen dorsal and
seven lumbar. The dorso-lumbar vertebra are always articu-
lated together by their zygapophyses, and there is a com-
plete sacrum.

The sternebre are numerous and laterally compressed.

In the skull the nasal bones are well developed, and have
the ordinary form. When supraorbital enlargements of the
frontal exist, they are of moderate size. The parietals unite
in a long sagittal suture. The orbit and the temporal fossa
communicate freely, the posterior boundary of the orbit never
being completed by bone. The jugal bone is large and unites
by a broad surface with the maxilla, There is a distinct

THE CARNIVORA. 351

coronoid process, and the long axis of the articular surface
which receives the head of the mandible is transverse.

The hyoid has a small body and many-jointed anterior
cornua.

Both pairs of limbs are fully developed, and the tail is not
provided with a horizontal fin. Clavicles may be absent, and,
when ossified, they do not occupy more than half the interval
between the acromion and the sternum. The scapula has a
distinct spine, and a large supra-spinous fossa.

Neither the hallux nor the pollex is opposable. The car-
pal and tarsal bones have the ordinary number and arrange-
ment; except that, in the carpus, the scaphoid and lunare are
united into one bone. The terminal phalanges of the digits,
which never fall below four in number, are almost always
provided with sharp and pointed claws.

The teeth are always distinguishable into incisors, canines,
and molars; they are lodged in distinct sockets, and their
crowns are covered with enamel. ‘There are always two sets
of teeth, a milk and a permanent dentition. Asa very general
rule, there are six incisors above and an equal number below.
The canines are long, curved, and pointed.

The stomach is simple and undivided, and the cecum,
which is never large, may be altogether absent.

The liver is deeply subdivided, and there is a gall-bladder.

In the brain, the cerebellum is never completely covered by
the cerebral hemispheres, which are connected by a large
corpus callosum, and, except in the aquatic forms, by a well-
developed anterior commissure. On the exterior of each
hemisphere, there are usually three distinct convolutions sur-
rounding the Sylvian fissure. But, in the aquatic Carnivora,
the gyri are much more numerous and complicated ; the cere-
bral hemispheres are much broader and longer in proportion
to the length of the brain; and they may even exhibit a rudi-
ment of the posterior cornu. In all these respects they ap-
proach the Cetacea.

The inferior turbinal bones are always large and have a
complicated form.

There are no -vesiculz seminales, and an os penis is very
generally present. The ovary is enclosed in a peritoneal sae.

The Carnivora are divisible into the Pinnipedia, or aquatic
Carnivores; and the /%issipedia, which are mainly terrestrial
and cursorial.

a. In the Fissipedia the incisors are, with one exception

. »7 . e 8°83 . e . .
(Zinhydris, ine Sea-otter, with @. =), six in number in each jaw.

852 THE ANATOMY OF VERTEBRATED ANIMALS.

The hind-limbs have the position usual in mammals, ard
the tail is free to its root. The pinna of the ear is fully de-
veloped. The middle, or outermost, digits of the pes are
longest, the hallux being shorter than the others. .

Almost invariably, the distal phalanges of both limbs are

y= SS
Soy SSpeeh

:

in

Fie. 107.—Skeleton of the Lion (Fedés Zeo),

i;

y)

aX

provided with claws; and, in the most thoroughly carnivorous
forms, these claws are very strong, curved, and pointed, The
phalanx which supports the claw has a similar form, and a

THE ANATOMY OF THE DOG. ‘Sid

plate of bone rises from its base as a short sheath. An elastic
ligament connects the base of the ungual phalanx with the
middle phalanx, so that, when the flexor profundus digitorum
is not in action, the ungual phalanx is pulled back upon the
middle phalanx, and the claw which it bears is retracted into
an integumentary sheath.

The olfactory lobes are usually large and the cerebral hemi-
spheres elongated.

As the Dog (Canis familiaris) is an excellent and easily
accessible example of a fissipede carnivore, it may be useful to
mention some of the more important points in its anatomy.

The vertebral column contains twenty dorso-lumbar ver-
tebree, of which thirteen are dorsal and seven lumbar, three
sacral, and eighteen to twenty-two caudal vertrebre. The
atlas has broad and rounded ale, the anterior margins of
which are deeply excavated near the roots. The posterior
edge of the spinous process of the axis vertebra is almost per-
pendicular and very thick.

Nine pairs of ribs are usually connected by sterno-costal
cartilages with the sternum, which is composed of eight lat-
erally-compressed sternebree. Only two of the three anchy-
losed sacral vertebree articulate with the ilia.

As in the Carnivora in general, the occipital foramen is
placed at the posterior end of the skull, and looks almost
directly backward. The sagittal and lambdoidal crests are
greatly developed and meet in a prominent occipital spine ;
the zygomata are very wide and arched outward; and the
coronoid process of the mandible is very large. The size of
these parts is in relation to the magnitude of the muscles of
the neck and jaws.

The ramus of the mandible is nearly straight, the proper
angle of the jaw being obsolete. A supra-angular process
projects outward from the ascending portion of the ramus,
and takes the place of the proper angle. The articular
condyle is much elongated transversely, narrow and convex
from before backward; and the pre- and post-glenoidal pro-
cesses of the squamosal are produced downward so as to
convert the joint into a complete ginglymus and to restrict
the motion of the jaw to the vertical plane. The supra-orbital]
processes of the frontals are small and pointed. The root of
the alisphenoid is traversed by a longitudinal canal. The tym-
panum is bounded below by a convex osseous wall, which is
termed the bulla. It opens externally by the short external

354 THE ANATOMY OF VERTEBRATED ANIMALS.

meatus, at the inner end of which is a circular elevation for
the attachment of the tympanic membrane. A short distance
internal to this frame for the membrane of the drum, a low
crest rises from the floor of the bulla and imperfectly divides
it into an outer and anterior portion which communicates
with the Eustachian tube, and an inner blind spheroidal cavity
which occupies the greater part of the bulla. The part of the
bulla which forms the floor of this cavity is the result of the
ossification of a process of the periotic cartilage, while the
other part is furnished by the tympanic bone. The low crest
is produced by the conjunction of both. Posteriorly and in-
ternally, the periotic region of the bulla presents a canal,
through which the internal carotid artery passes. The pos-
terior opening of the carotid canal looks into the foramen
lacerum posticum, and is not visible without dissection.
There is a large paroccipital process, with a prominent free
extremity ; but, for the greater part of its length, it is closely
applied to the back of the bulla. The condyloid foramen is
quite distinct from the foramen lacerum posterius. A large
foramen behind the glenoidal cavity transmits a vein from the
interior of the skull. In the nasal cavity, the ethmoidal turbi-
nals are very large; the superior turbinals are prolonged into
the great frontal sinus, and the inferior turbinals unite, in the
middle line, with the septum.

The clavicles of the Dog are always rudimentary, and are
generally represented only by a gristly intersection of the
muscles which represent the sterno-mastoid and deltoid.

The olecranar fossa of the humerus is perforated. The
hallux is much shorter than the other digits. When the Dog
stands, the metacarpal bones of these digits are nearly verti-
cal; the basal phalanges are horizontal; the middle and the
distal phalanges are inclined in the form of a V with the apex
(the articulation between the two) downward. The claws
are, consequently, raised from the ground, the foot resting
partly on a thick integumentary pad, which lies beneath the
basal phalanges; and, partly, on the under surfaces of the
joints between the middle and the distal phalanges. The dis-
tal phalanges are kept bent upon the middle ones by elastic
ligaments, which pass from one to the other, and which an-
tagonize the action of the long flexors. The Dog, therefore,
possesses the mechanism for the retraction of the claws, but
its action is not sufficient to protect them from wear. Labelle,
or sesamoid bones developed in the tendons of the gastrocne-
mius, lie behind the condyles of the femur. ‘The fibula is thin

THE MYOLOGY OF THE DOG. 305

and closely applied to, but not anchylosed with, the tibia.
The hallux is usually rudimentary; only the metatarsal, and
the basal phalanx, being represented by two small ossicles.
In some breeds of dogs, however, the hallux is fully developed.

In the myology of the Dog the insertion of the tendon of
the external oblique muscle of the abdomen presents some in-
teresting peculiarities. The outer and posterior fibres of this
muscle end in a fascia which is partly continued over the
thigh as fascia lata, and partly forms an arch (Poupart’s liga-
ment) over the femoral vessels ; by its inner end it is inserted
into the outer side of a triangular fibro-cartilage, the broad
base of which is attached to the anterior margin of the pubis,
between its spine and the symphysis, while its apex lies in
the abdominal parietes. The internal tendon of the external
oblique unites with the tendon of the internal oblique to form
the inner pillar of the abdominal ring, and is inserted into the
inner side of the triangular fibro-cartilage. The pectineus is
attached to the ventral face of the cartilage; the outer part
of the tendon of the rectus into its dorsal face; but the chief
part of that tendon is inserted into the pubis behind it. This
fibro-cartilage appears to represent the marsupial bone, or
cartilage, of the Monotremes and Marsupials.

The trapezius and the sternomastoid coalesce into a single
muscle; and, in the absence of a complete clavicle, the outer
fibres of the latter and those of the anterior part of the del-
toid are continuous. In this way a muscle which has been
called levator humert proprius is formed. The omohyoid and
the subclavius are absent. There is a trachelo-acromialis and
a dorso-epitrochlearis. The supinator longus is absent, but
there is a pronator quadratus. The extensor communis digi-
torum mands divides into four tendons, in which sesamoid
bones are developed over the articulations between the first
and second phalanges. The extensor primi internodii pollicis
is absent. The extensor secundi internodii is one muscle with
the extensor indicis. 'The extensor minimi digiti sends ten-
dons to the third, fourth, and fifth digits. All these deep ex-
tensors have sesamoid bones over the metacarpo-phalangeal
articulations. The palmaris longus appears to be absent;
but all the other flexors of the manus, even the palmaris bre-
vis, are represented. The tendons of the flexor pollicis longus
aud flexor digitorum perforans are united. The divisions
which the common tendon sends to the five digits develop
sesamoid bones, just before their insertions into the bases of
the distal phalanges. The fifth digit has its abductor, flexor

356 THE ANATOMY OF VERTEBRATED ANIMALS.

brevis, and opponens ; the pollex, an abductor, adductor, flexor
brevis, and, perhaps, an opponens. The second, third, and
fourth digits have each a pair of jflexores breves, which repre-
sent the interossei, and are inserted into the bases of the prox-
imal phalanges, a relatively large sesamoid being developed
in each, Each sends off a fine tendon dorsad to the extensor
sheath. The plantaris is large, and, as in the Pig, its tendon
passes into the representative of the flexor brevis digitorum
pedis. ‘The tendons of the flexor hallucis longus and jlexor
perforans unite into a common tendon, which subdivides into
slips for the digits.

. eae 1—1 4s
The dental formula of the Dog is «4¢ = p.m. 7-4

ee) . : . :
M, 5~3—42. The two upper inner incisors, on each side, have ~

distinctly trilobed crowns—the lateral cusps of the crown
arising from outgrowths of the cingulum at its base. The
outer incisor is larger than the others, and its middle cusp is
very large, while the outer is rudimentary. The large canine
has a strong, curved, pointed crown, with a longitudinal ridge
along its posterior face. The crowns of the anterior three
premolars are triangular, with a smooth-cutting anterior edge;
the hinder edge is also sharp, but is divided by a notch into
two lobes, of which the hinder is the smaller. These teeth
are two-fanged. The fourth premolar is a large tooth. In
form, its crown has a general similarity to that of the fore-
going; but, firstly, the posterior lobe is relatively much larger,
and pointed, so as to form an obvious second cusp; and, sec-
ondly, a strong process of the crown projects inward from its
anterior end, and is supported by a distinct fang—so that this
premolar is three-fanged. It is termed a carnassial, or secto-
rial, tooth, as it bites like a scissors-blade against a corre-
sponding tooth in the mandible. The preceding teeth have
cutting crowns; but those of the molars are broad and crush-
ing. They exhibit an outer division, formed by two large
subequal cusps, and an inner division, also presenting two
cusps, the posterior of which is much smaller than the ante-
rior. In addition, the cingulum sends up a strong process on
the inner side of the crown.

In the lower jaw, the crowns of the incisors, the outer of
which is the largest, are all trilobed. The outer cusp is
stronger than the inner in all, and particularly in the outer
incisors. The canines resemble those of the upper jaw. Each
premolar has two fangs and a sharp triangular crown, the pos-
terior edge of which is trilobed, as in the upper premolars;

THE DENTITION OF THE DOG. 357

but the posterior lobe is small in the fourth, which differs but
little fromthe rest. ‘The first molar, on the other band, is a
large tooth, with a blade-like crown, which bites against the
inner side of the upper fourth premolar, and is called the
carnassial or sectorial tooth of the lower jaw. The crown is
elongated, and presents a large anterior external cusp, divided -
into two lobes by a deep notch. On the inner side of this is
a small internal cusp. The two posterior cusps are very much
lower than the anterior ones, and form a sort of heel to the
blade-like anterior portion of the crown. An oblique ridge
connects the outer and larger of the two posterior cusps with
the small inner and anterior cusp. The second molar has a
broad quadricuspidate crown, the inner posterior cusp being
almost obsolete. The crown of the last molar is small, simple,
and obtusely conical.

It thus appears that the sectorial, or carnassial, teeth in
the two jaws differ in their nature, the upper being the last
premolar, and the ig the anterior aes The milk denti-

tion of the Dogis di. 25 dc. = dm. =, the “ first premolar”

of the adult dendition fyi ng no deciduous predecessor; so
that, in this, as in so many other cases, it is doubtful whether
it ought to be counted in'the milk, or in the adult, dentition.
The middle deciduous molar in both j jaws resembles ‘the hinder-
most premolar of the adult dentition, and the hindermost, the
first molar of the adult. The so-called “ first premolar ” of the
adult, and the anterior molars, appear before any of the decid-
uous molars are shed,

The czecum of the Dog is long, and folded upon itself, in
which respects it is unlike that of other Carnivores. The arch
of the aorta gives off an anonyma and a left subclavian.

In the brain, the olivary bodies are inconspicuous, the
corpora trapezoidea large, and the corpora mammillaria dis-
tinctly double. The olfactor y lobes are very large, and ex-
pand posteriorly on the sides of the brain into a broad mass
continuous with the gyrus uncinatus, or hippocampal lobule.
The cerebral hemispheres extend for a considerable distance
over the cerebellum, in the upper view, and overlap it later-
ally. The Sylvian fissure does not extend more than half-way
to the median fissure. The surface which answers to the
insula is quite smooth. The anterior ends of the calloso-mar-
ginal sulci pass on the upper surfaces of the hemispheres, and
give rise to the “crucial” sulcus, There are three principal
gyri upon the outer surfaces of the hemispheres; one which

358 THE ANATOMY OF VERTEBRATED ANIMALS.

immediately bounds the Sylvian fissure, one which runs along
the upper margin of the hemisphere, and one between these
two. ‘The corpus callosum is long, and the anterior commis-
sure well developed.

There is a musculus choanoides in addition to the usual
ocuiar muscles, and the rudimentary nictitating membrane is
said to possess a muscle.

The tensor tympani arises from a deep pit above the prom-
ontory, and its tendon passes directly outward to the mal-
leus.

The male is devoid of Cowper’s glands. The penis has a
bone, and the glands becomes swollen during copulation, so as
to prevent the withdrawal of the penis from the vagina of the
female. The ovary of the female is enclosed in a sac of the
peritonzeum, and the uterus has long cornua. The umbilical
sac is drawn out toa point at each end. ’

The Dogs (including the Wolves, Jackals, and Foxes, under
this head) form the most central group of the Carnivora, which
may be termed the Cynoidea.* From these the Bears,
Weasels, and Procyonide depart, on the one hand, and the
Cats, Civets, and Hyzenas on the other. The former group
(Arctoidea) have the cavity of the bulla tympani undivided
by aseptum. ‘The paroccipital process is not applied to the
posterior wall of the dud/a. The mastoid process is widely
separated from the paroccipital. The condyloid foramen is
not merged in a common opening with the foramen lacerum
posticum. ‘The intestinal canal is devoid of a cecum. The
large penis has a bone which is not grooved; there are ne
Cowper’s glands, and the prostate is small.

In the latter group (Adluroidea) the bulla tympani is large
and rounded, and the septum, which is rudimentary in the
Cynoidea, is so much enlarged as to leave only a narrow
aperture of communication between the two chambers. The
par-occipital is closely applied to the posterior wall of the budla.
The mastoid process is often obsolete. The condyloid foramen
opens into a fossa common to it and the foramen lacerum
posticum. All have a short cecum. The penis is small, and
its bone small, irregular, or absent. They have Cowper’s
glands and a well-developed prostate.

The Cynoidea are all digitigrade, and resemble the Dog
in their dentition. The Arctoidea are plantigrade, while the

* See Prof. Flower’s important memoir on the Classification of the Car
nivora in the Proceedings of the Zoological Society for 1869.

ee

THE PINNIPEDIA. 359

Ailuroidea are for the most part digitigrade, but may be plan-
ticrade. In dentition, each of these groups presents forms
such as the Bears on the one hand, and the Cats on the other,
which may be regarded as extreme modifications, in opposite
directions, of the type exhibited by the Dog.

In the Bears, the dental formula is the same as in the
Dogs, but the crowns of the teeth are all more obtuse. The
sectorial teeth lose their marked characters, and the molars
have flat and tuberculated crowns. The anterior premolars
fall out as age advances. It is a remarkable circumstance that
the teeth of frugivorous and carnivorous Bears exhibit no such:
differences as would lead to a suspicion of their complete
difference of habit, if we were acquainted with these animals
only in the condition of fossils.

3°3 1—1

The Cats have the dental formula «4.3365 p.m 35
m. ~ = 30. The canines are very long and sharp. The pre-

molars are like the Dogs’, except that they are sharper, and
that the hindermost (the sectorial tooth) has hardly any in-
ternal process. The single upper molar is a small tooth with
a flat, transversely-elongated crown, and it lies within, as well
as behind, the great sectorial premolar. In the lower jaw, the
sectorial, or first, molar is the last tooth in the series, The
crown is a deeply-bifurcated blade representing the antero-
external cusp of the corresponding tooth in the Dog. The
“heel” is obsolete.

While the Bears are among the most completely planti-
grade of the Carnivora, the Cats are most entirely digitigrade,
and the apparatus for the retraction of the ungual phalanges
is so well developed that the claws are completely retracted
within sheaths of the integument, when the animal does not
desire to use them. To this end the elastic ligaments are very
strong, and the median phalanx is excavated, in order to allow
of the lodgment of the retracted phalanx on one side of it.

b. The Pinnipedia, or Seals and Walruses, are those Car-
nivora which come nearest the Cetacea. The tail is united,
by a fold of skin which extends beyond its middle, with the
integument covering the hind-legs. These are, in most
species, permanently stretched out in a line with the axis of
the trunk. The pinna of the ear is small or absent. The toes
are completely united by strong webs, and the straight nails
are sometimes reduced in number, or even altogether abortive.
The inner and the outer digits of the pes are very large. The
incisors vary in number and lose their cutting form. The pre:

360 THE ANATOMY OF VERTEBRATED ANIMALS.

molar and molar teeth are similar in character, and never
have more than two fangs. There is no lachrymal bone or
canal,

The brain-case of the cranium is generally much more
rounded than that of other Carnivora ; and, in some genera,
the supra-orbital processes of the frontals are very largely
developed. In both of these characters, and in the great
breadth and complication of the convolutions of their cerebral
hemispheres, as well as in their relatively small olfactory
nerves and anterior commissure, the Pinnipedia approach the
Cetacea.

There are three groups of Pinnipedia: the Otaride, the
Trichechide, and the Phocide.

1. The Otauride, or Eared Seals, are so termed because the
ear possesses a distinct though almost rudimentary pinna.
These Seals have long necks, and can stand or walk upon all
fours, the hind-limbs being capable of supporting the body in
the ordinary way.

In many respects, these animals are closely allied with the
Bears; and by no part of their organization is this more clearly
shown than by the skull, which in its general form, its large
supra-orbital processes, the small and rugged bulla tympani,
the perforation of the alisphenoid by a canal, and the presence
of a crest on the inner surface of the parietals, is extremely
ursine.

2. The Trichechide, or Walruses, are devoid of external
ears, but resemble the Otaride@ in their mode of standing and
walking. The skull resembles that of the Bear in the same
respects, but the muzzle is distorted by the enormous develop-
ment of the superior canines. The Walruses resemble the
Bears in another point, namely, in the presence of a supple-
mentary bronchus; the right bronchus, before it reaches the
lung, dividing into two trunks, a large and a small. The thy-
roid cartilage is deeply excavated, in front, by a triangular
fissure ; and the epiglottis is extremely small.

In the brain, the remarkably large and richly convoluted
hemispheres cover the cerebellum, and present a rudimentary
posterior cornu. The anterior commissure is very small, as
are the olfactory nerves.

The dentition of the Walrus is extremely peculiar. Inthe
adult, there is one simple conical tooth in the outer part of the
premaxilla, followed by a huge tusk-like canine, and three,
short, simple-fanged teeth. Sometimes, two other teeth,
which soon fall out, lie behind these, on each side of the upper

THE PHOCIDA. 261

jaw. In the mandible there are no incisors, but a single short
canine is followed by three, similar, simple teeth, and by one
other, which is caducous.

1—1

The dental formula is therefore 7. = Ci p.m. =

3. The Phocide, or ordinary Seals.—The pinna is alto-
gether absent. The hind-limbs are permanently stretched
out, parallel with the tail; and, consequently, they are unable
to support the body, or assist in locomotion on land.

The space between the orbits is extremely narrow, and
supra-orbital processes are absent. The bulla tympani is very
large and thick-walled ; and the middle are much shorter than
the outer digits of the pes.

The common Seal (Phoca vitulina) is a native and acces-
sible member of this group. It has a rounded head anda
neck which is well marked, though shorter in proportion than
that of the Eared-seals. The nasal apertures are slit-like and
can be closed at will, the eyes large and brilliant, and the
auditory apertures small and devoid of a pinna, The limbs
are large, and their distal longer than their proximal divis-
ions. ‘The fore-limb is buried beyond the elbow in the com-
mon integument, but the flexible wrist allows the weight of
the body to be supported by the palmar surface of the manus.
The hind-limbs, on the contrary, are permanently extended
and turned backward parallel with the tail, which lies between
them, and with which they form a sort of terminal fin, When
the Seal swims, in fact, the fore-limbs are applied against the
sides of the thorax, and, the hinder moiety of the body being
very flexible, the conjoined hind-limbs and tail are put to the
same use as the caudal fin of a Cetacean. The Seal has twenty
dorso-lumbar vertebree, of which five are lumbar. There are
four sacral vertebrae, but only one of these unites with the ilia.
Hleven vertebre enter into the formation of the short tail.
There are ten true ribs and nine sternebree, the manubrium
being prolonged forward into a long cartilaginous process.

The brain-case is smooth, rounded, and spacious, but the
cranium narrows rapidly in the interorbital region. Its floor
is remarkably flattened from above downward and very thin,
the broad basi-occipital sometimes presenting a perforation in
the dry skull. The falx is partially, and the tentorium is wholly,
ossified. The occipital segment is very large, and the supra-
occipital advances between the parietals, but does not separate
them completely. The alisphenoids are small and almost hori

16

362 THE ANATOMY OF VERTEBRATED ANIMALS.

zontal, and the synchondrosis between the basisphenoid and
presphenoid persists. In all these respects the Seal’s skull is
strikingly cetacean. In fact, if the supra-orbital processes
were sawn off, a Porpoise’s brain-case would closely resemble
a Seal’s. But the nasal bones and the parietals are large, and
the ethmoidal region is very peculiar. The lamina perpen-
dicularis is largely ossified, and the vomer soon becomes ossi-
fied into one mass with it. The two ethmoidal turbinals (or
the superior and middle) are small and flattened, and the lat-
ter anchyloses with the vomer on each side. The inferior, or
maxillary, turbinal is extremely large and complicated, and it
blocks the nasal passage in front of the others like a sieve, or
strainer. There is no lachrymal bone, but the jugal is large.
The squamosal is anchylosed with the periotic and tympanic.
The latter is massive and shell-shaped, somewhat as in the
Cetacea, but it has rather different relations to the auditory
meatus. The periotic is very large, and its tumid pars mas-
toidea appears largely on the exterior of the skull. The fossa
under the superior vertical semicircular canal is prolonged into
this tumid part of the periotic.

The alveolar portions of the premaxille are very small, but
these bones extend far up the sides of the anterior nares.
The maxillz do not extend over the frontals. The mandible
has a well-developed coronoid process.

The pollex is the longest and strongest digit, the others
oradually decreasing in length. The fifth metacarpal articu-
lates with the cuneiform bone, as well as with the unciform.

The ilium is short, and the long pubis and ischium are
ereatly inclined backward, so that the long diameter of the os
innominatum makes only an acute angle with the spine. The
femur is much shorter than the humerus. The tibia and fibula
are anchylosed, and more than twice as long as the femur.
The pes is longer than the tibia. The astragalus has a pecul-
iar, roof-shaped, tibial surface, and sends a process backward
which contributes to the formation of the very short heel.
The hallux is the strongest of the digits; while this and the
fifth digit are the longest of those of the pes.

The cutaneous muscle is largely developed and inserted
into the humerus. The pectoralis major is very large, and
arises from each side of the prolonged manubrium, and even
in front of it, beneath the neck; the fibres of the muscles of
opposite sides are continuous. The palmaris longus is a strong
muscle, but the proper digital muscles are weak or absent, as
in the case of the abductor, adductor, flexor brevis, and oppo:

THE PHOCID.A. 363

nens of the fifth digit. A special long abductor of this digit,
however, passes from the olecranon to the distal phalanx. The
liacus is wanting, and there is no psoas major ; but muscles
which represent the psoas minor and the subvertebral muscles
of the Cetacea are very large and play an important part in
effecting the locomotion of the Seal. The pectineus is very
small, and the other adductors are inserted, not into the femur,
but into the tibia. The glutwus maximus is inserted into the
whole length of the femur. The semi-membranosus and semi-
tendinosus are replaced by a caudo-tibialis, which arises from
the anterior caudal vertebrae and is inserted into the tibia,
some of its tendinous fibres extending to the plantar aspect
of the hallux. The poplitewus and gastrocnemius are strong,
but there is no soleus. The tendon of the plantaris passes
over the calcaneum and ends on the plantar fascia of the per-
forated tendon of the fourth digit. The other perforated ten-
dons seem to arise from the fascia attached to the calcaneum.

The dental formula is ¢. =} ¢ 5 mp.m. 3 = 34.

The grinding teeth have triangular crowns with notched
edges, and at most two fangs.

The milk-teeth are shed during foetal life, and at this
period there are three molars above and below on each side,
which appear to be replaced by the second, third, and fourth
of the adult set. If such be the case, only the hindermost of
these last will be a true molar,

The tongue is bifid at the extremity. The cesophagus,
very wide and dilatable, passes without any very well-marked
line of demarcation into the stomach, which is a great pyri-
form sac with its pyloric end bent upon itself. The intestine
is about twelve times as long as the body. The colon is
short, and is provided with a cecum. The liver is divided
into a great number of lobules, which are, as it were, set upon
the inferior cava. The latter vessel, just below the diaphragm,
presents a great dilatation, into which the venw hepatice of
the several lobules open. After traversing the diaphragm,
the vena cava is surrounded, for about an inch, by a layer of
red circular muscular fibres. The aorta and the pulmonary
artery are both dilated at their commencements.

The penis of the male is contained within a prepuce, sup-
ported by a loop of the cutaneous muscle. There is a large
os penis, which presents a groove for the urethra inferiorly.
The prostate is small, and there are no vesiculz nor Cowper’s
glands. The testes lie just outside the inguinal canal. The

364 THE ANATOMY OF VERTEBRATED ANTMALS.

anus and the vulva of the female are surrounded by a common
fold of integument. The clitoris has no bone. The body of
the uterus is divided by a longitudinal septum.

_ IL. The Proboscidea.—These are massive animals, walking
upon the extremities of the five toes, with which each foot is
provided, and upon a great tegumentary cushion which unites
these, and forms a flat sole behind them.

g
;
|
;

Fig. 108.—The skeleton of the African Elephant (Lowodon Africanus).

The nose is prolonged into a flexible proboscis, which is at
once a strong, and a delicate, organ of prehension. The hairy
covering is scanty in the recent species; but there were abun-

ee 2 Se ee

THE PROBOSCIDEA. 3865

Jant long hair, and an undercoat of wool, in at least one
extinct Proboscidean, the Mammoth (Hlephas primigenius),
which ranged over Northern Europe and Asia during the gla-
cial epoch. The pinna of the ear is large and flat. The testes
of the male remain in the abdomen, and the mammez of the
female are placed between the fore-limbs.

The dorso-lumbar vertebrz amount to as many as twenty-
three, and not more than three of these are lumbar, so that the
dorsal region is, proportionally, exceedingly long. There are
four sacral vertebrae, followed by a comparatively short tail. The
centra of the vertebrz are far more flattened, from before
backward, than those of any other terrestrial mammal, and
this is particularly the case in the cervical region, whence it
follows that the neck is extremely short.

The skull is enormous, even in proportion to the body, its
size arising, in great measure, from the development of air cav-
ities in the diploe. The interspace between the inner and the
outer tables of the skull is often, in an old elephant, consider-
ably greater than the diameter of the cerebral cavity itself.
The cranial cavity is elongated and subcylindrical. The supra-
occipital-rises far upon the roof of the skull, so that the pari-
etals are much narrower at the sagittal suture than elsewhere.
The premaxillz are very large, and the nasal bones short, the
nasal passages being nearly vertical. The jugal bone forms
only the middle part of the jugal arcade. The rami of the
mandible have a high perpendicular portion, and they are
largely anchylosed at the symphysis, which is produced into a
sort of spout.

The acromion of the scapula has a recurved process, such
as is frequently found in the Rodents, to which order the Pro-
boscidea present many curious approximations. There are
no clavicles. In the antebrachium, the radius is permanently
fixed (though not anchylosed) in the prone position, crossing
the ulna obliquely. The carpal and metacarpal bones, and
the phalanges, are remarkable for their short and thick form,
and the manus is larger than the pes.

The ilia are immensely expanded transversely. The femur,
which is not connected by any round ligament to the acetabu-
lum, is relatively long and slender; and, when the animal is
at rest, is directed perpendicularly to the axis of the trunk,
not bent up, so as to form an acute angle with that axis, as it
is in ordinary quadrupeds. The ham consequently occupies
the middle of the length of the hind-leg ; the flexion of which,
at this point, when the animal walks, gives an elephant a gait

366 THE ANATOMY OF VERTEBRATED ANIMALS.

which is strikingly different from that of other quadrupeds,
The tibia is relatively short. The fibula is distinct and com-
plete, and the bones of the pes have the same broad and short
form as those of the manus. The hallux has only a single
phalanx in some species.

The Proboscidea have only two kinds of teeth, incisors and
molars, canines being entirely absent. The incisors are com-
posed of dentine and cement, with or without a longitudinal
belt of enamel, and, in the recent Elephants, are developed
only in the upper jaw. As their growth continues for a long
period, or throughout life, they usually take the form of long
tusks, which project on each side of the upper jaw. The
molar teeth are composed of dentine, enamel, and cement, and
their crowns, when unworn, are always ridged, the ridges. very
often being made up of distinct tubercles. The intervals be-
tween the ridges are sometimes, as in the Asiatic Elephant,
exceedingly deep, narrow, and completely filled up with
cement; or, as in the African Elephant, they may be shallow
and open, the cement forming only a thin coat. In the recent
Elephants, only the two incisors are preceded by milk-teeth.
The molars are, altogether, six on each side, above and below ;
they come into place and use successively, the hinder ones
moving forward, in proportion as the anterior ones are worn
down by the attrition of those which are opposed to them.

The stomach is simple and elongated, and there is a very
wide cecum. The trilobed liver has no gall-bladder. The
heart has two anterior cave.

The cerebellum is left uncovered by the cerebral hemi-
spheres; which, in the existing Elephants, are large, and have
greatly-convoluted surfaces,

The male reproductive organs exhibit two very large ve-
siculz seminales, and four prostates. The uterus of the female
has two cornua,

Some, if not all, species of the extinct genus Mastodon
were provided with a pair of short tusks in the mandible, in
addition to the large ones in the premaxille. And in some of
these animals, as in certain other extinct Elephants, the an-
terior grinding teeth had vertical successors, The Miocene
genus, Dinotherium, possessed two large, downwardly-direct-
ed tusks, one on each side of the symphysis of the mandible,
while there were none in the upper jaw. The second and the
third anterior grinding teeth had vertical successors.

The Proboscidea are, at present, restricted to Asia and
Africa, where they are represented by two very distinct forms,

eo Se ee ee eee Pe

Can es i ee

a _
je A Te a tes oe oe

THE HYRACOIDEA. 367

to which the names of Loxodon (i. Africanus) and Huelephas
(Z. Indicus) proposed by the late Dr. Falconer may be very
properly applied. The oldest rocks in which their remains
occur are of Miocene age. Fossil remains of elephants occur
not only in the Old World, but also in both North and South
America.

Ill. The Ayracoidea.—The genus Hyrax, which is the
sole member of this group, was referred by Pallas to the Ro-
dents; and by Cuvier, who demonstrated that it could not bea
Rodent, it was placed among the Ungulata, in the immediate
neighborhood of AAinoceros, without any better evidence than
that afforded by the characters of the molar teeth. Prof.
Brandt, of St. Petersburg, in an elaborate memoir just pub-
lished, arrives at the conclusion that it is a “ gliriform Ungu-
late,” intermediate, in a certain sense, between the Lodents
and the Ungulata; but, still, more Ungulate than Rodent. It
appears to me to be neither Ungulate nor Rodent, but the
type of a distinct order, in many respects intermediate be-
tween the Ungulata, on the one hand, and Rodentia and In-
sectivora, on the other.

The small, Rabbit-like, animals comprised in the genus
Hyrazx are plantigrade, and provided with four visible toes in
front and three behind. The nails are not hoof-like, but
nearly flat, except the innermost of the hind-foot, which is
peculiarly curved. The body is covered with fur, and the
muffle, or snout, is split, as in the Rodents. There is a pen-
dulous penis, but no scrotum; and there are four inguinal and
two axillary teats.

There are from twenty-nine to thirty-one dorso-lumbar
vertebrae, which is the greatest number known in any terres-
trial mammal. Twenty-one or twenty-two of these are dorsal.
No mammal, except Choleepus, the two-toed Sloth, possesses
so large a number of dorsal vertebre as this. The transverse
processes of the last lumbar vertebra articulate with the
sacrum, as is the case in many Ungulate Mammals. In the
skull, the post-orbital processes, which are chiefly furnished by
the parietal and the jugal, nearly meet. Part of the articular
facet for the mandible is formed by the jugal, which extends
forward until it comes into contact with the lachrymal bone.
The base of the external pterygoid process is perforated by a
canal, as in Perissodactyla and Lemuridw. ‘There are large
pre- and post-tympanic processes, and the post-tympanic is
much shorter than the par-occipital process. The premaxillz
are large, and unite extensively with the nasal bones; the

368 THE ANATOMY OF VERTEBRATED ANIMALS. |

perpendicular ramus of the mandible is very wide, and some-
what like that of the Tapir in shape. The posterior margin
of the bony palate is opposite the anterior edge of the last
molar tooth.

The scapula is devoid of an acromion process, as in the
Perissodactyla. There are no clavicles, but the coracoid pro-
cess is well developed. ‘The ulna is complete, and a rudiment
of the pollex is present. In the carpus, a line prolonging the
axis of the third metacarpal bisects the os magnum and the
dunare, which is not the case in any Ungulate Mammal.

In the hind-limb, the femur possesses a small third tro-
chanter, which is not nearly so conspicuous as in some Ro-
dents. The tibia and fibula are complete. The extremity of
the inner malleolus articulates with a shelf-like process of the
astragalus, the distal face of which bone has no facet for the
cuboid. The digits 7. and v. are not represented even by rudi-
ments. The terminal phalanx of 7. is longitudinally cleft.

The dentition of the adult is 7. 30.25 p.m. pay and
m.;-, The outer upper incisors are very small, and soon
fall out; the inner, which are very large, curved, and have a
thick coat of enamel on their anterior faces, continue to grow
throughout life, as in Rodeuts. The lower incisors have
crowns denticulated at the edges, like those of Gialeopithecus
and some Bats. They bite upon a callous pad which lies be-
hind the upper incisors. The patterns of the upper and lower
molar teeth are very similar to those of the corresponding
teeth in Rhinoceros. As in the Horse, part of the Hustachian
tube is dilated into a thin-walled sac extending on the inner
side of the bulla tympani from the pterygoid processes to the
exit of the ninth nerve.

A slight constriction marks off the cardiac from the pyloric
division of the stomach. The cardiac portion is lined by a
dense epithelium. The intestine is provided with three ceca
—one in the ordinary position, and two placed much lower
down on the colon, opposite one another, and terminating by
pointed ends. There is no gall-bladder. The ureters open,
not near the neck of the bladder as in Mammals generaily, but
near the fundus, as in some few Rodents,

The male has vesicule seminales, prostatic and Cowperian
olands. The uterus is two-horned, and the vulva and anus are
surrounded by a common fold of integument.

In the foetus the yelk-sac and the vitello-intestinal duct
zarly disappear. The amnion is not vascular. The allantois

ST WE er ea ne

THE RODENTIA. 369

spreads over the interior of the chorion, and gives rise to the
broad zone-like placenta, which is composed of both maternal
and foetal parts. The maternal vessels pass straight through
the thickness of the placenta toward its foetal surface, on
which they anastomose, forming meshes, through which the
vessels of the foetus pass tow ard the uterine surface of the
placenta.

The species of the genus Hyrax are found only in Syria
and Africa. No fossil A yracoidea are known.

The DiscompEa.—The Mammalia with discoidal placentze
are the Rodentia, the Cheiroptera, the Insectivora, and the
Primates,

1. The Roprent1a.—This large group of Mammalia is most
definitely characterized by its dentition. There are no canines,
and the mandible never contains more than two incisors, which
are placed one on each side of the symphysis, and continue to
grow throughout life. They are coated with enamel much
more thickly upon their front surfaces than elsewhere; so
that by attrition they acquire and retain a chisel-shaped edge,
the enamel in front wearing away less rapidly than the rest
of the tooth.

With the exception of one group of Rodents, there are only
two teeth in the premaxillze; and these have the same char-
acters as the incisors of the mandible. The Lagomorpha, or
Hares and Rabbits, however, have a second pair of incisors
of small size, behind the first, in the upper jaw. The molars
are from two to six in number, in each half of the upper jaw,
and two to five, in the lower jaw. They consist of enamel,
dentine, and cement, and their crowns may be tuberculate or
laminate in pattern. Sometimes they form roots, but, in other
cases, they grow throughout life. Where there are more than
three grinding-teeth, the one which precedes the three hinder-
most has displaced a milk-tooth; but, where the grinding-
teeth are fewer than three, or only three, none of them dis-
place a milk-tooth. Even when milk-teeth exist they may
be shed before birth, as in the Guinea-pig.

The premaxillary bones are always large, and the orbits
are never shut off by bone from the temporal fossa. Very
generally, the condyle of the mandible is elongated from be-
fore backward.

With the exception of one group, the Dormice (Myoxine),
all Rodents have a large ceecum.

The cerebral hemispheres leave the cerebellum largely
uncovered, when the brain is viewed from above. They are

870 THE ANATOMY OF VERTEBRATED ANIMALS.

either smooth externally, or very moderately convoluted,
The corpus callosum is well developed.

With the exceptions noted, the foregoing characters are
universal among the Lodentia. There are other peculiarities
which are generally present, and, when they exist, are very
characteristic, though they are not universal.

Thus the dorso-lumbar vertebrz are usually nineteen in
oumber. There is a large interparietal ossification. The
jugal bone is comparatively short, and occupies only the mid-
dle of the zygomatic arch.

The clavicles are very generally present; though wholly
absent in some genera, as, for example, the Guinea-pig,
(Cavia). 'The acromion commonly sends a process backward
over the infra-spinous fossa. ‘There is a ninth bone in the car-
pus intercalated between the proximal and the distal series,
The digits are five, ungulate, and provided with small claws.

There is a bone in the penis. The testes do not leave the
abdomen, but come down into the groin in the breeding-sea-
son. Vesiculze seminales and prostatic glands are present.
In the female the uterus is, in many genera, completely di-
vided into two cornua, each of which opens separately into
the vagina; but, in the rest, the cornua unite into a corpus
uteri.

Some genera depart widely from the rest in particular
points ; for example, in the Porcupines, the hairs on the dor-
sal region of the body are very much enlarged, acquire a pe-
culiar structure, and formed the so-called “ quills.” Some of
the Porcupines have prehensile tails.

In Cavia and Hydrocherus the toes are reduced to three,
and the nails have almost put on the character of hoofs.

The Squirrels have the short pollex almost opposable.

The femur in some Rodents has:a well-developed third
trochanter; and in Dipus, the Jerboa, the long metatarsals
become anchylosed together into a cannon-bone.

In the Porcupines, the suborbital foramen is enormous,
and an anterior fasciculus of the masseter muscle arises from
the maxilla, and traverses the foramen to its insertion.

The Hamster ( Cricetus) has great cheek-pouches, provided
with special retractor muscles connected with the spines of
two lumbar vertebree.

In some genera, the stomach, which is usually simple, tends
to become complex. Thus the cardiac division of the stomach
of the Beaver is provided with a special glandular mass. The
cardiac end of the cesocphagus of the Dormouse is glandular

THE ANATOMY OF THE RABBIT. STE

and dilated like the proventiculus of a bird. And, in Arvicola,
the stomach becomes deeply constricted, and a groove leads
from the cesophagus toward the pyloric end, reminding one
of certain Artiodactyla.

In some few genera, the ureters open into the fundus of
the bladder, or near it.

Although the genera and species of the fodentia are
more numerous than those of any other mammalian order;
and although they are adapted to very different modes of life—
some, like the “ Flying Squirrels,” floating through the air by
means of a parachute-like expansion of the integument be-
tween the fore- and hind-limbs; others being arboreal, like the
ordinary Squirrels; or among the swiftest of runners, as the
Hares; or strong burrowers, as the mole-like Lathyergus ;
or aquatic, like the Water-vole—their structural differences
are comparatively insignificant, and the subdivision of the
order into large groups is proportionately difficult.

Brandt has divided the Rodents according to their cranial
characters into Sctwromorpha, Myomorpha, Hystricomorpha,
and Lagomorpha ,; or, Squirrels, Rats, Porcupines, and Conies,
if we use these English names in a broad and tribal sense.

The student will find the Rabbit, one of the Lagomorpha,
to be a conveniently-sized and easily-obtained subject for study.
The following are the most important points to be noted in
its structure: The hairy covering of the body extends over
the palmar and plantar regions of the feet, and into the interior
of the mouth, so that there is a band of hair on the inside of
each cheek. There are five digits on the fore-foot, or manus;
but the pollex is smaller than the others. The pes has only
four digits, and the hind-limb is longer than the fore-limb.
The upper lip is large, flexible, and cleft in the middle line;
the large eyes are provided with a third eyelid, and the pinnz
of the ears are very long and mobile. The tail is short and
recurved. The male has a recurved penis, and on each side
of it a scrotal sac. The female has five pair of abdominal teats.
In both sexes perineal glands are present, consisting of a
saccular involution of the integument with rugose walls, into
which the duct of a special gland lodged at the side of the
penis, or of the clitoris, opens.

There are nineteen dorso-lumbar vertebrze, of which twelve
are dorsal. Of the four sacral vertebrz only the first unites
with theilia. The dorsal vertebra have well-developed spinous
and transverse processes. At about the eighth, a mammillary
process, or metapophysis, becomes obvious ; and in the succeed-

B72 THE ANATOMY OF VERTEBRATED ANIMALS.

ing vertebree this increases in length and strength, till in the
lumbar region it becomes as long as the spinous process. In
the last lumbar, it is short, and in the sacrum it is obsolete,
but it is traceable through the series of the anterior caudal
vertebre. Accessory processes, or anapophyses, are observa-
ble in the last dorsal and four or five anterior lumbar vertebree.
The transverse processes of the lumbar vertebrze are exceed-
ingly long, and that of the first lumbar is bifurcated at its ex-
tremity. These transverse processes give attachment above,
to the sacro-lumbalis, and below, to the psoas major, both
which muscles are very large;. while the heads of the longis-
simus dorsi are attached to the long metapophyses. The great
mass of these extensor and flexor muscles of the spine, and
the leverage afforded by the mode of their attachment to the
long processes of the vertebree, would seem to be related to
the leaping and scratching movements of the Rabbit. Strong
median processes are developed from the ventral faces of the
centra of the three anterior lumbar vertebree ; these give attach-
ment to the crura of the diaphragm.

The tubercles of the second to the eighth ribs inclusively
are prolonged into spiniform processes, which give attachment
to the tendons of the longissimus dorsi. There are five ster-
nebrze and a long xiphoid process. ‘The manubrium is long,
narrow, deep, and keeled inferiorly.

In the skull, the great supra-orbital processes of the frontal
are to be noted. The presphenoid is high and greatly com-
pressed from side to side, so as to forma thin septum between
the orbits, and the optic foramina run into one, as In some
Seals. The tympanic and the periotic are anchylosed together,
but remain distinct from the adjacent bones, and are merely
held in position by abutting against the basi-sphenoid on the
inner side and by the post-tympanic hook of the squamosal on
the outside. The tympanic is prolonged upward and outward
into a tubular meatus. The glenoid cavity is elongated from
before backward. ‘The suture between the jugal and the
maxillary becomes obliterated, and there is no orbital process
given off from the zygoma. A considerable extent of the
outer wall of the maxilla remains incompletely ossified. The
premaxilla is extremely large and trifurcated.

The ascending portion of the ramus of the mandible is long,
and the coronoid process well developed. The long axis of
the condyle is antero-posterior, and the angular process has a
slight inward projection. In the palate, the prepalatine, or
incisive foramina are enormous; and partly in consequence of

THE MYOLOGY OF THE RABBIT. 373

this, partly by the posterior excavation of the palatal plate of
the palatine, the roof of the palate is reduced to little more
than a transverse bar of bone.

The scapula is long and narrow, and the backward process
of the acromion, to which reference has already been made,
gives attachment to a slip of the trapezius. A bony clavicle
is present, but itis incomplete at both ends. There is a supra-
condyloid foramen in the humerus. The radius and ulna are
complete, but are fixed in the attitude of pronation.

The femur has a small third trochanter. The tibia and
fibula are anchylosed. The internal cuneiform bone is want-
ing, and the plantar surface of the naviculare gives off a large
process. ‘The inner side of the base of the second metatarsal
sends a process along the inner face of the meso-cuneiform to
articulate with the naviculare. This may represent a rudiment
of the hallux with the ento-cuneiform.

In the myology of the Rabbit the vast size of the flexors
and extensors of the back has already been noted. The mus-
cles moving the fore- and especially the hind-limbs, and the
masseter, are not less remarkable for their dimensions. In the
fore-limb, the supinator longusis absent. The extensor indicis
and secundi internodit pollicis form one muscle. The extensor
minimi digitt goes to the fourth and fifth digits, The flexor
perforans and the flexor pollicis longus unite in a common
tendon which divides into five slips, one for each digit. There
are three lumbricales from the radial sides of the tendons for
the third, fourth, and fifth digits. The flexor sudlimis, or per-
foratus, for digits 77., 777., and iv., arises from the inner con-
dyle as usual; but that for the fifth digit springs from the
pisiform bone—thus simulating the ordinary arrangement of
the perforated flexor in the pes. There is no pronator quad-
ratus ; but the palmaris longus is distinct, and its slender ten-
don expands into the palmar aponeurosis. Each digit, except
the pollex, has a pair of flewores breves, or interossei, which lie
on the palmar faces of the metacarpal bones.

In the hind-limb, the so/eus has only a fibular origin. The
plantaris is very large and ensheathed in the gastrocnemius;
it ends in a tendon nearly as large as the tendo Achillis,
which passes over the end of the caleaneum, being connected
with this and the tendo Achillis by a strong fascia laterally,
but being otherwise separated from it by a synovial sac. In

he sole of the foot it divides into four tendons, which be-
come the perforated tendons of the four digits. The flexor
perforans and flexor hallucis are fused into one muscle, the

374 THE ANATOMY OF VERTEBRATED ANIMALS.

tendon of which divides in the sole into the four perforating
tendons. There are three lumbricales, and four pair of dnéer-
osset (flecores breves). There is no proper tibialis posticus,
but a muscle arises from the upper part of the inner face of
the tibia, internal to, and in front of, the insertion of the pop-
litceeus, becomes tendinous about the middle of the leg, passes
behind the inner malleolus, and runs along the inner and dor-
sal aspect of the second metatarsal to be inserted into the ex-
tensor tendons. It seems to stand in the same relation to the
second digit as the peroncwus quinti, on the opposite side of
the pes, to the fifth digit. The peronceus longus is inserted
into the base of the second metatarsal: a peronceus brevis, p.
guarti, and p. guinti digiti, are present. ‘There is no extensor
hallucis longus, nor any extensor brevis digitorum.

The principal characters of the brain of the Rabbit have
already been described (see p. 60, and Figs. 21 and 22).
There is a single large corpus mammillare. Of the corpora
quadrigemina, the nates are larger than the testes. There is
a very large and completely-exposed flocculus, and the vermis
is large in proportion to the lateral lobes of the cerebellum.
The corpora trapezoidea are well marked.

The membrana nictitans is very large, has a convex free
edge, and contains a triangular cartilage. There are no
puncta lachrymalia, but a crescentic aperture leads into the
lachrymal canal. The large lachrymal gland lies above and
external to the eyeball, and there is a well-developed Harde-
rian gland on its lower and inner side.

. e 22 0—0 3°3 3°3
Vhe dental formula is’%. 7, ¢ Gap 0:7: a5 Me aq =

The lower, and the inner upper, incisors are very large and
long; they grow continuously from persistent pulps, and they
are coated with enamel only in front, so that wear keeps them
constantly sharp. The second pair of small incisors exists
only in the upper jaw. A great diastema separates the inci-
sors from the first premolar above and below. The grinding-
teeth all grow from persistent pulps, and do not form fangs;
they have transversely-ridged crowns, the patterns of which
are very similar throughout, the first and the last only pre-
senting some differences. The young Rabbit bas three inci-
sors and three milk-molars on each side, in the upper jaw. In
the lower jaw, there are only two milk-molars on each side.

The stomach is simple, and there is a large czecum. Spe-
cial glands pour their secreticns at the side of the anus.

The pancreas is very large, and its duct enters the intes-

|
|
|

THE INSECTIVORA. 375

tine nearly a foot from the pylorus, and far distant from the
biliary duct.

There are two anterior cave; and the external jugular
vein is very much larger than the internal.

In the male, the inguinal canal remains permanently open,
and there is a large uterus masculinus. In the female, the
uteri are quite separate, and each opens by a distinct os tince
into the vagina.

The distribution of the Rodentia is almost world-wide,
Madagascar being the only considerable island in which indi-
genous Rodents are unknown. The Austro-Columbian provy-
ince may be regarded as the headquarters of the group.

Remains of Rodents have been found, in the fossil state,
as far back as the eocene formation.

II. The Insecrivora.—It is exceedingly difficult to give
an absolute definition of this group of Mammals. But all the
Insectivora possess more than two incisors in the mandible;
and their molar teeth, which are always coated with enamel,
have tuberculated crowns, and form roots.

The fore-limbs have the structure usual among ungui-
culate Mammals; and, in both limbs, the digits are provided
with claws. The hallux is not opposable, and, like the other
digits, it is provided with a claw.

In addition to these distinctive characters there are others
which are met with in all members of the group.

The Jnsectivora are, almost all, either plantigrade or semi-
plantigrade. The clavicles are completely developed in all,
except Potamogale. The stomach is simple. The testes of
the male are either inguinal or abdominal, and do not descend
into a scrotum. The female has a two-horned uterus.

The cerebral hemispheres leave the cerebellum uncovered,
in the upper view of the brain; and are almost, or wholly,
devoid of sulci and gyri. The corpus callosum is sometimes
exceedingly short.

No Insectivore attains a large size, and some, such as the
Shrew Mice, are the smallest of the Mammalia.

The Jnsectivora present a great diversity of organization,
the common Hedgehog being an almost central form. The
Shrews tend toward the Rodentia, the Tupaye toward the
Lemurs; while the Moles, on the one hand, and the Galeo-
pithect on the other, are aberrant modifications, Relations of
a more general character connect them with the Carnivora
and the Ungulata.

376 THE ANATOMY OF VERTEBRATED ANIMALS.

The Hedgehog (Zrinaceus Huropcus) is pentadactyle and
plantigrade. It has along flexible snout. The eyes are
small; the pinne of the ears are rounded, and the integument
lining the concha is produced into a transverse, shelf-like fold,
The under surface of the body bears hairs of the ordinary
kind; but, on the dorsal aspect of the head and trunk, the
hairs are converted into strong fluted spines. There are
twenty-one dorso-lumbar vertebrz (of which fifteen are dor-
sal, and six lumbar), three or four sacral, and twelve to four-
teen caudal. Accessory processes, or metapophyses, are de-
veloped on several of the dorso-lumbar vertebra. The sterne-
bree are laterally compressed, except the manubrium, which is
broad ; and eight of the fifteen pair of ribs are connected with
the sternum.

The occipital foramen is placed completely at the hinder
extremity of the skull, in the lower part of the perpendicular
occipital face of the cranium, and looks backward. ‘There are
large paramastoid processes. .The glenoidal surface for the
mandible is flattened. The zygoma is stout, and the jugal
bone is, as it were, applied upon the outer side of it. The
orbit has no posterior osseous boundary. The lachrymal fora-
men lies upon the face. There are unossified spaces in the
bony palate, and the posterior margins of the palate are thick-
ened, as in the Lemurs. The large and bullate tympanic bone
does not anchylose with the squamosal, or the periotic, and is
readily lost from the dry skull. The alisphenoid contributes
largely to the formation of the front wall of the tympanum ;
and a large portion of the inner wall of the tympanic cavity is
formed by a broad process of the basisphenoid, the outer and
lower edge of which joins, by a sort of harmonia, with the
inner and lower edge of the tympanic.

The ascending portion of the ramus of the mandible is
short, and the angle is slightly inflected. The two rami are -
not anchylosed at the symphysis. The supra-scapular fossa is
wider than the infra-scapular. The spine is strong, and the
acromion bifurcates, sending a prolongation backward. The
clavicles are long and convex forward. The humerus has an
intercondyloid foramen; but there is no foramen above the
inner condyle, and this circumstance is unusual among the
Insectivora. The bones of the antibrachium are fixed in tke
prone position. There is an os centrale in the carpus, so that
it has nine bones. The scaphoid and lunare are anchylosed,
as in the Carnivora, and the pisiform bone is much elongated,
The pollex and the fifth digit are the shortest.

ead
amet,

THE MYOLOGY OF THE HEDGEHOG. 377

The pelvis is remarkably spacious. The symphysial union
of the pubes is always small, and, sometimes, the bones remain
separate. The subpubic arch is much rounded. ‘The ilium is
narrow, and a mere ridge separates the iliac fossa from the
gluteal surface. The femur has a round ligament, and a
prominent ridge represents a third trochanter. The distal
ends of the tibia and fibula are anchylosed together.

One of the most notable peculiarities of the Hedgehog is
its power of rolling itself up into a ball, from all sides of
which the spines protrude. This is effected, for the most part,
by the contraction of the greatly-developed cutaneous muscle,
the chief fibres of which are disposed as follows: A very
broad band, the orbicularis pannicult, encircles the body lat-
erally. In front, it partly arises from the nasal and frontal
bones, and partly is the continuation of a thick mass of fibres
which pass over the occiput. Posteriorly, each lateral division
of the muscle spreads out into a very broad band, which is
thick ventrally and thin dorsally, and adheres closely to the
skin, from the line at which the hairy and spinigerous surfaces
join, to near the median line of the back. Posteriorly, the
two lateral halves of the orbicular muscle pass into one an-
other upon the distal half of the short tail.

The action of this muscle will depend upon the attitude
of the animal when it contracts. If the head and tail are fully
extended, the orbicularis can only diminish the dimensions of
the spinigerous region of the skin and erect the spines. But
if the head and tail be more or less flexed, as they always are
in the ordinary attitude of the Hedgehog, the orbicularis will
play the part of a powerful sphincter, approximating the
edges of the spinigerous area toward the centre of the ventral
side of the body, and forcibly enfolding the trunk and limbs
within the bag thus formed. It is, in fact, the chief agent in
coiling the body up, and keeping it so coiled.

Numerous muscular bundles take a radiating direction on
the dorsal aspect of the body, and antagonize the orbicularis:
1. A pair of slender occipito-frontales arise from the occipital
crest, and are inserted into the integument over the frontal
and nasal bones. 2. A pair of occipito-orbiculares arise from
the same crest, and pass into the anterior part of the orbicu-
laris. 3. A pair of broader cervico-orbiculares arise from
the fascia of the neck, and pass to the dorsal part of the an-
terior fourth of the orbicularis, 4. Slender dorso-orbiculares
arise close to the hinder ends of the trapeziz and spread out
above the foregoing. 5. Two stout muscles, coccygeo-orbicur

378 THE ANATOMY OF VERTEBRATED ANIMALS.

ares, arise from the middle caudal vertebree, and, after re-
ceiving fibres from the ventral region, end in the dorsal mar-
gins of the orbicularis. 6. Two muscles attached to the
pinne of the ears (auriculo-orbiculares) pass backward to the
orbicularis on each side.

On the ventral aspect are certain muscles which assist the
orbicularis: 1. Two broad muscles (sterno-faciales) arise in
the middle line, over the anterior part of the sternum, and
pass outward and forward to the sides of the lower jaw and
the integument of the face and ears. Muscular slips from
these are sent up over each shoulder to the orbicularis. 2. A
humero-abdominalis arises from each humerus beneath the in-
sertion of the pectoralis major, and, passing backward over
the sides of the abdomen, these become connected with the
ventral edges of the orbicularis. 'The external fibres of these
muscles are continued round the ischial regions to the coccy-
geo-orbicularis ; the internal fibres pass to the prepuce, and
over the middle line of the abdomen, in front of it. 3. A hu-
mero-dorsalis arises from the humerus close to the foregoing,
and, passing upward and backward through the axilla, spreads
out in the mid-dorsal integument and the orbicularis,

The contraction of all these muscles must tend to bring
togther the edges of the integumentary bag, and to tuck the
head, tail, and limbs into it.

In the myology of the limbs the following points are note-
worthy: The supinator longus, pronator teres, and palmaris
longus, are absent. The palmaris brevis is present. A single
muscle takes the place of the extensor secundi internodii polli-
cis and extensor indicis, and sends a third tendon to the mid-
dle digit. The extensor minimi digiti supplies the other two
digits. The flexor perforans and flexor pollicis longus are rep-
resented by five distinct muscular heads, each with a tendon
of its own; but all the tendons unite in the middle of the fore-
arm, and the common tendon again subdivides into only four
slips, the pollex receiving no tendon. There are no lumbrica-
les. The pollex has only a rudimentary flexor brevis and an
abductor. The other digits have each two interossei, or flex-
ores breves, inserted into the metacarpo-phalangeal sesamoids.

In the leg, the solews has only a fibular head, and the flexor
brevis digitorum arises wholly from the calcaneum, The flexor
hallucis and flexor perforans have a common tendon, which,
in the sole, divides into five tendons, one for each digit.
There are no lumbricales, nor flexor accessorius. The tibialis
posticus seems to be represented by twe small muscular bel-

THE BRAIN OF THE HEDGEHOG. 379

ies, one of which arises from the prominent end of the tibia,
and the other from that of the fibula. The tendons of both
pass behind the inner malleolus, and that of the former mus-
cle goes to the tibial and plantar surface of the hallucal meta-
tarsal, while the latter is inserted into the ento-cuneiform
bone. The interossei pedis are represented by a pair of jflex-
ores breves for each digit except the hallux.

The adult Hedgehog has thirty-six teeth, of which twenty
are in the upper, and sixteen in the lower jaw. The dental
0—0
0—0

: « 3°3 4—4 3°3
aernls 1%, .-, Co —, P.N. =, M. aa —= OO.

The grinding surface of the crowns of the first and second
upper molars exhibits a pattern fundamentally similar to that
of the corresponding teeth in Man, the Anthropomorpha, and
the majority of the Lemurs; that is to say, there are four
cusps, and the antero-internal is connected with the postero-
external cusp by an oblique ridge. The cusps are remarkably
sharp and pointed, and the outer surface of the postero-ex-
ternal one alone is somewhat inflected.

In the lower jaw, the corresponding molars are each marked,
as in most Lemurs, by two transverse ridges. In front of the
anterior ridge is a basal prolongation of the tooth, on to which
a curved ridge is continued inward and forward from the an-
terior principal ridge, giving rise to an imperfect crescent with
its convexity outward.

According to Rousseau there are twenty-four milk-teeth,

i. a.m. > which fall out seven weeks after birth.

The brain of the Hedgehog is remarkable for its low or-
ganization. The olfactory lobes are singularly large, and are
wholly uncovered by the cerebral hemispheres; which, on the
other hand, do not extend back sufficiently far to hide any
part of the cerebellum. Indeed, they hardly cover the corpora
quadrigemina. Only a single shallow longitudinal sulcus
marks the upper and outer surface of each hemisphere. On
the under surface, a rounded elevation corresponds with the
base of each corpus striatum. Behind this, another elevation
represents the end of the uncinate gyrus and the termination
of the hippocampus major; and therefore answers, in a man-
ner, to the temporal lobe. The inner face of the hemisphere
presents neither convolution nor sulcus, except -behind and
below, where a very broad jon follows the contour of
the fissure of Bichat and or: represents the dentate

sulcus. Above, this sulcuSends behind the posterior margin

380 THE ANATOMY OF VERTEBRATED ANIMALS.

of the corpus callosum. The latter is remarkably short, and
directed obliquely backward and upward. It has no genv, and
the pre-commissural fibres of the ventricular wall spread out,
beneath its anterior end, upon the face of the hemisphere.
The part of the corpus callosum which answers to the lyra is
very thick in proportion, and is inclined at an acute angle to
the rest.

In a transverse section, the corpus callosum is seen to be
very thin, and to curve upward and outward into the roof of
the ventricular cavity. The inner walls of the lateral ven-
tricles, which answer to the septum lucidum, are thick, while
the fornix is comparatively thin and slender. The anterior com-
missure is very stout. In this circumstance, as in the small
corpus callosum, the brain of the Hedgehog closely approaches
that of the Didelphia and Ornithodelphia, There is no trace
of a posterior cornu, or calcarine fissure, and the lateral ven-
tricle extends forward into the olfactory lobe. The optic nerves
are very slender; the corpora geniculata externa are large and
prominent; the nates are smaller than the testes, and trans-
versely elongated. The cerebellum has a large vermis and
small lateral lobes; the floccwli are prominent and are lodged
in fossee of the periotic bones. The pons Varolii is very
small; the corpora trapezoidea proportionally large.

The spinal cord is remarkable for its thickness, and, at the
same time, for its brevity, as it ends in the middle of the dorsal
region, As a consequence of this arrangement, the cauda
eguina is particularly large and long.

The stomach is simple, but the mucous membrane of the
considerable cardiac dilatation is thrown into numerous, and
very strong, longitudinal ruge. The intestine is about six
times as long as the body, and presents no distinction into
small and large; nor is there any caecum. The liver is
divided by deep fissures into six lobes; a central one which
bears the gall-bladder, a bifid spigelian lobe, and, on each side
of these, two other lobes. The pancreas is a large and
irregularly-ramified gland; and the spleen is elongated and
trihedral.

The pericardium is extremely thin. The arteries arise
from the arch of the aorta, as in Man, by an anonyma, a left
carotid and left subclavian. The course of the internal
carotid is remarkable. When it reaches the base of the skull
it enters the tympanum and there divides into two branches,
of which one traverses the stapes, and, passing forward in a
groove of the roof of the tympanum, enters the skull and gives

THE SPLANCHNOLOGY OF THE HEDGEHOG. 881

rise to the middle meningeal and ophthalmic arteries. The
other branch passes over the cochlea, enters the skull by a
narrow canal near the sella turcica, and unites with the circle
of Willis.

The external jugular vein is very much more capacious
than the internal, the latter being very small and hardly
traceable to the internal jugular foramen. It is by the external
jugular vein, in fact, that the great mass of the blood within
the skull is carried away, a foramen in the squamosal bone
allowing of a free communication between the external
jugular vein and the lateral sinus. There is a left superior
vena cava, which winds round the base of the left auricle,
receives the coronary vein, and opens into the right auricle.
The vascular system thus retains many embryonic characters.

The right lung is four-lobed ; the left may possess from one
to three lobes.

Two ossifications, one on each side of the opening for the
aorta, occur in the diaphragm.

The testes of the male do not leave the cavity of the
abdomen, but they descend as far as the inner side of the in-
guinal ring, to which they are connected by a short guber-
naculum and cremaster. The vasa deferentia descend to the
base of the bladder and then enter a hollow muscular sheath
on their way to a “chamber,” which is lodged in the distal
end of that sheath. This “chamber” passes into the penial
urethra; the cystic urethra opens into it by a narrow slit in
its front wall; and it receives the ducts of three pair of
appendages. The proximal pair consist of a multitude of
ramified tubuli, which have been found to contain sperma-
tozoa, and are usually regarded as vesicule seminales. The
middle pair (the so-called “ prostatic glands”) have a similar
structure and have also been observed to contain spermatozoa.
The lowermost pair are Cowper’s glands. The ‘“ chamber”
appears to represent the urogenital sinus of the embryo, which
has not become differentiated into prostatic and bulbous
urethra.

The ovaries are enclosed in wide-mouthed peritoneal sacs,
and a ligamentous band, the diaphragmatic ligament, extends
from the ovary to the posterior surface of the diaphragm.
The cornua uteri are large and long. There are five pair of
teats; the anterior pair being axillary and the posterior
inguinal, The other three pair are equidistant, and lie along
the ventral surface, internal to the edge of the orbicularis pan
niculi,

382 THE ANATOMY OF VERTEBRATED ANIMALS.

Like the Rodentia, the Insectivora have a great diversity
of habit; some G‘aleopitheci flitting through the air after the
fashion of the flying Squirrels ; some arboreal, as the Tupaye ;
some terrestrial and cursorial, like the majority of the order.
A few are swimmers; and some, like the Mole, are the most
completely fossorial of Mammals.

The most aberrant form of the Jnsectivora is the genus
Galeopithecus, essentially an Insectivore of arboreal and
frugivorous habit, with very long and slender limbs. These
are connected with one another, with the sides of the neck and
body, and with the tail, by a great fold of the imtegument,
which is called patagium ; and, unlike the web of the Bat’s
wing, is hairy on both sides, and extends between the digits
of the pes. By the help of this great parachute-like expan-
sion, the @aleopithecus is enabled to make floating leaps,
from tree to tree, through great distances. When at rest,
the Galeopithect suspend themselves by their fore- and hind-
feet, the body and the head hanging downward; a position
which is sometimes assumed by the Marmosets among the
Primates.

The fore-limbs are slightly larger than the hind-limbs.
There are four axillary teats. The male has a pendent penis
and inguinal scrotal pouches. The pollex and the hallux are
short, and capable of considerable movement in adduction and
abduction, but they are not opposable; and their claws are
like those of the other digits.

The occipital foramen is in the posterior face of the skull.
The orbit is nearly, but not quite, encircled by bone. The
lachrymal foramen is in the orbit. The bony roof of the palate
is wide and its posterior margin is thickened. There is a
strong curved post-glenoidal process of the squamosal, which
unites with the mastoid, beneath the auditory meatus, and
restricts the movement of the mandible to the vertical plane.
A longitudinal section of the skull shows a large olfactory
chamber projecting beyond that for the cerebral lobes, and two
longitudinal ridges, upon the inner face of the latter, prove that
these lobes must have possessed corresponding sulci. The
tentorial plane is nearly vertical and the floccular fossee are
very deep.

The ulna is very slender inferiorly, where it becomes anchy-
losed to the distal end of the radius, which bears the carpus.
When the ilia are horizontal, the acetabula look a little up-
ward and backward as well as outward. The fibula is com:
plete. As in the Sloths and most Primates, the navicular and

GALEOPITHECUS. 383

cuboid readily rotate upon the astragalus and calcaneum, so
that the planta pedis is habitually turned inward.

The dental formula is ¢. 5 ¢ (5 p.m. m. = = 34.

The outer incisor, in the upper jaw, has two roots, a
peculiarity which is not known to occur elsewhere. The
canines of both jaws also have two roots, as in some other
Insectivora. The lower incisors are single-fanged ; and their
crowns are broad, flat, and divided by numerous deep longitu-
dinal fissures, or “ pectinated.”

The length of the whole alimentary canal from mouth to
anus is not more than six times that of the body. The sac-
culated caecum is as long as the stomach, and its capacity
must be greater than that of the latter organ.

Galeopithecus has, at one time, been placed among the
Lemurs, and at another, among the Bats. But the resem-
blances with the former are general and superficial, and the
differences in the form of the brain, the dentition, the structure
of the limbs and of the skull, exclude it from the order of the
Primates.

Galeopithecus agrees with the Bats in the disposition of
the tail, and in the existence of a patagium provided with
special muscles. Further, in a slight obliquity of the acetab-
ula, such as is seen in its extreme development in the Bats;
in the imperfect condition of the ulnz; and in the pectoral
position of the teats and the pendent penis. Both of these
last, however, it must be recollected, are also Primatic charac-
ters. Finally, the somewhat similarly pectinated lower incisor
teeth are found in the Cheiropteran genera, Diphylla and

Desmodus.
But G‘aleopithecus differs from the Bats completely in the
structure of the fore-limbs; in the position of the hind-limbs
and the absence of a calcar ; in the two-fanged outer incisors
and canines; and in the presence of a cecum,

On the other hand, the peculiarities of the skull and brain
are mainly insectivorous, as is the two-fanged canine; and 1
see no reason for dissenting from Prof. Peters’s view that Gal-
eopithecus belongs neither to the Primates, nor to the Chei-
roptera, but that it is an aberrant Insectivore.

With respect to other Jnsectivora, it is worthy of note,
that Macroscelides has the radius and the ulna anchylosed.
The Tupaye possess a large cecum. Chrysochloris has pec-
toral mammary glands; Centetes and the Moles have the penis
pendent.

384 THE ANATOMY OF VERTEBRATED ANIMALS.

The Zupayce are soft-furred, long-tailed, tree-loving ani-
mals, with complete bony orbits and a large cecum, and are
those Jnsectivora which most nearly approach the Lemurs.

The Shrews (Sorices) most nearly resemble Rodents out-
wardly, being very like small mice. The zygoma is imperfect,
the tibia and fibula are anchylosed, and the pubic bones do not
meet in the symphysis. There are sixteen to twenty teeth in
the upper jaw and twelve in the mandible. Canines are
absent, and there are six incisors above and four below. The
inner lower incisors are greatly elongated and proclivous, and
some of the teeth not unfrequently become anchytosed with
the jaws. There is no czecum, and peculiar musk-glands are
sometimes developed at the sides of the body.

The Moles (Zalpine) have no external ears, and the eyes
are rudimentary. ‘The fore-limbs are much larger than the
hind, and are inclosed within the integument up to the carpus.
The palmar surface of the broad manus is turned outward and
backward.

a

BR xe
‘

Fia. 199.—The skeleton of a Flying-Fox (Pteropus).

The manubrium of the sternum is very broad, and its ven-
tral surface gives rise to a strong median crest. The scapula
is as long as the humerus and the radius together. It is tri-
quetral and possesses an acromial process, but no distinct cor

THE CHEIROPTERA. 385

racoid. The clavicle, which is very strong, is perforated by a
great foramen, and at the middle of its posterior margin sends
off a truncated reéntering process. - Proximally, it furnishes
an articular surface for the humerus. In the carpus there is a
distinct centrale, and a large accessory C-shaped bone lies on
its radial side. The pubes are separate at the symphysis, and
an accessory styloid bone is connected with the naviculare of
the foot.

The distribution of the Jnsectivora is singular in this
respect, that, although they are met with, under very various
climatal conditions, throughout the Old World and North
America, there are none in South America or Australia.

In the fossil condition they are not certainly known to
occur in strata older than the tertiary. hie

II. The Currrorrera.—The Cheiroptera may be regard-
ed as exceedingly-modified Insectivora, having their nearest
ally in Galeopithecus,

They possess one or two pair of pectoral teats; and the
fore-limbs are very long, some of. the digits particularly being
immensely elongated. There is a patagium, or expansion of
the integument, uniting the fore-limbs with the body, and ex-
tended, as a membranous web, between the elongated fingers,
Of these, the third, fourth and fifth, and very frequently the
second, are devoid of nails. The pollex always has a claw-
like nail. When the animal is resting upon the ground, the
thigh is twisted upward and backward, in such a manner that
its extensor face looks forward, and its flexor face backward.
In consequence of this the knee looks upward and backward,
and the toes are turned backward and slightly outward. Un-
der the same circumstances, all the digits of the manus are
flexed upon their metacarpal bones; and the folded-up wing
rests against the side of the body, while the pollex, with its:
claw, is extended forward. In this position the animal shuffles
along, with considerable rapidity; hauling itself forward by
the claws on the pollices, and shoving itself along, by extend-
ing the hind-limbs.

The favorite attitude of a Bat, when at rest, however, is
that of suspension by the claws of one or both legs, with the
head downward and the patagium folded over it like a cloak.
The most active movement of the Bat is effected by flight, the
fore-limbs being extended, and the patagium, which they sup-
port, playing the part of the feathers of a bird’s wing.

The gk a as are remarkably large in proportion

1

386 THE ANATOMY OF VERTEBRATED ANIMALS.

to the others, but, as in the rest of the vertebral column, the
spinous processes are very short. The ribs are long and
curved, so as to include a relatively capacious chest. The
manubrium of the sternum is very wide, and the middle of its
under surface raised into a crest. In the lumbar region, the
vertebral column is bent, so as to be concave forward and to
describe almost the quarter of a circle. As a consequence, the
axis of the sacrum is at right angles to that of the anterior
thoracic vertebree.

In the skull, the orbit is not divided by bone from the
temporal fossa, and the premaxillz are relatively small, and
sometimes altogether rudimentary.

The clavicles are remarkably long and strong, and the
broad scapula has a strong spine. The ulne are imperfect
distally, the carpus being borne altogether by the radius.
There is only a single bone in the proximal row of the carpus,
the pisiform being absent. Those digits of the manus which
are devoid of nails possess not more than two phalanges.

The pelvis is very narrow and elongated, and the pubic
bones are widely separated at the symphysis, as in some Jn-
sectivora. ‘The anterior caudal vertebrz and the ischia are
frequently united. The axes of the acetabula are directed
toward the dorsal side of the body as well as outward;
whence, in part, arises the peculiar position of the thigh,
which has already been described. The fibula is rudimentary,
its upper part being represented only by ligament, and there
is an elongated bone, or cartilage, attached to the inner side
of the ankle-joint which lies in and supports the patagium,
and is called the calecar. The distal moiety of the tarsus
readily rotates upon the astragalus and calcaneum, permitting
the sole to turn inward with much ease.

All Cheiroptera possess three kinds of teeth, incisors,
canines, and molars; and the intestine is devoid of a caecum.

The heart is provided with two superior cave, a right and
left; and the smooth cerebral hemispheres leave the cerebel-
lum completely exposed.

The testes are abdominal throughout life, or may descend
into the perineum, but there is no true scrotum. The penis
is pendent. ‘There are vesiculze seminales. The form of the
uterus varies, being sometimes rounded and sometimes two-
horned.

The Bats are ordinarily divided into the Frugivora and
the Jnsectivora.

a. The Hrugivora live, as their name implies, exclusively

Ls

THE CHEIROPTERA. 387

upon fruits. With the single exception of Hypoderma, all
-the genera embraced in this group have a nail on the second

digit of the manus, and the crowns of the molar teeth, which
soon wear down, are, when entire, divided by a longitudinal
furrow.

'. The incisors do not exceed >.

The pyloric portion of the stomach is immensely elongated.

The nose has no foliaceous appendages, and the well-
developed pinna of the ear has the ordinary form, neither the
tragus, nor any other part, being unusually developed.

These Bats are confined to the hotter parts of the Old
World and of Australia, where, from their dog-like heads and
reddish color, they are known as “ Flying-Foxes ” (Pteropus,
Harpyia, etc.).

b. The division of the Insectivora contains Bats which, for
the most part, live upon insects, though some delight in fruits,
and others suck the blood of larger animals.

The second digit of the manus is devoid of a nail, and
sometimes is without any bony phalanges.

- The stomach is usually pyriform, with a moderate cardiac

enlargement. The molar teeth almost always have such a
‘pattern as is observed in the typical Jnsectivora, and do

not exceed six, or fall below four, on each side above and
below.

The incisors are ordinarily 2) or [,
be much reduced.

The integument of the nose is developed into an append-
age which is sometimes very large and leaf-like, and the tragus
of the large ears is often similarly modified. The tail is often

but their number may

‘Jong, and sometimes prehensile.

The genera Desmodus and Diphylla (of which the group
Heematophilina has been formed) are the most completely
blood-sucking of all the Bats in their habits. They have a

- pair of enormous, sharp-pointed, upper incisors, while the four

lower incisors are small and pectinated. The canines are very

~-Jaree and sharp, and the molars, which are reduced to two

above and three below, on each side, have their crowns con-

verted into sharp longitudinally disposed ridges, like the
“edges of scissors. In Desmodus, the very narrow cesophagus

leads into a stomach which would be of extremely small di-
mensions, were it not that its cardiac end is dilated into a
great sac, which is longer than the body, and lies, folded up
on itself, within the cavity of the abdomen. Into this sac it

388 THE ANATOMY OF VERTEBRATED ANIMALS.

would appear that the blood swallowed by the animal at first
passes, to be thence slowly drawn along the intestine.

Mr. Darwin* thus speaks of the habits of Desmodus
D Orbignyi:

“The Vampire Bat is often the cause of much trouble by
biting the horses on their withers. The injury is generally
not so much owing to the loss of blood as to the inflammation
which the pressure of the saddle afterward produces. The
whole circumstance has lately been doubted in England. I
was therefore fortunate in being present when one was act-
ually caught on a horse’s back. We were bivouacking late
one evening near Coquimbo, in Chili, when my servant, noti-
cing that the horses were very restless, went to see what was
the matter, and, fancying he could distinguish something, sud-
denly put his hand on the beast’s withers and secured the
Vampire. In the morning the spot where the bite had been
inflicted was easily distinguished, from being slightly swollen
and bloody. The third day afterward we rode the horse with-
out any ill effects.”

IV. The Primares.—The Primates have two pectoral
mamme, and, rarely, additional ones upon the abdomen. In-
cisor and molar teeth are always present, and, with one excep-
tion, canines. ‘he incisors are never more than two, nor are
there more than three premolars and three molars, on each
side, above and below.

Saving individual exceptions, which occur in one genus,
and may be regarded as abnormal, the hallux possesses a flat
nail. The hallux differs in form from the other digits of the
foot, and is so disposed as to be capable of more or less exten-
sive motion in adduction and abduction; and, very generally,
it is opposable to the other digits of the foot.

The Primates are divisible into—a. the Lemurida, 6, the
Simiade, and ¢, the Anthropide.

a. The first of these divisions, the Lemurida@, is more
widely separated, anatomically, from the other two, than these
are from one another, and it contains some forms which
very closely approximate to the Jnsectivora, while others are
nearly affined to the Rodentia.

* *S Voyage of the Beagle,’? Mammalia, p. 2.

+ On the strength of these differences M. Gratiolet relegated the Lemurs to
the Jnsectivora; and Mr. Mivart, in his valuable paper ‘‘ On the Axial Skele-
ton in the Primates,’ published in the Proceedings of the Zoological Society
for 1855, divides the /rimates into two sub-orders, Lemuroidea and Anthro-

pordea,

THE LEMURID. 389

All the Zemuride are habitually quadripedal, have the
integument furry, and are usually provided with long tails
which are never prehensile. They are devoid of cheek-
pouches and of callous patches upon the integument covering
the ischia.

The fore-limbs are shorter than the hind-limbs. In the
foot, the hallux is large and opposable, and the second digit
differs from the rest in size, and in the claw-like form of its
nail, The fourth digit is usually longer than the others, the
difference being especially marked in the pes.

In the skull, the brain-case is small relatively to the face,
and is contracted anteriorly. If a straight line drawn from
a point midway between the occipital condyles, through the
median plane of the skull, to the junction of the ethmoid and
presphenoid, in the floor of the cerebral cavity, be termed the
basi-cranial axis ; and if the planes of the cribriform plate of
the ethmoid, of the tentorium cerebelli, and of the occipital
foramen, be respectively termed the ethmoidal, tentorial, and
occipital planes; then, the greatest length of the cerebral
cavity hardly exceeds the length of the basi-cranial axis; and
the ethmoidal, tentorial, and occipital planes are very much
inclined to that axis. The upper aperture of the lachrymal
foramen lies upon the face, outside the front margin of the or-
bit. The frontal and the jugal bones are united behind the or-
bit, but a mere bar of bone results from their union ; and it is
so narrow that the orbit and the temporal fossa are in free
communication. The bony palate is elongated, and, in many
species, its posterior free edge is thickened.

The lateral processes of the atlas are, usually, expanded.
The lumbar region of the spine is elongated; the vertebrze
composing it, in some cases, being as many as nine. There
are nine bones in the carpus. The ilia are narrow and elon-
gated, and the ischia are not everted. In most Lemurs, the
tarsal bones resemble those of the other Primates ; but, in
Otolicnus and Tarsius, they have undergone a modification, a
ee to which is not to be found among Mammals, but must

e sought among the Batrachia. When the distance between
the heel and the digits is great in other Mammalia, the elon-
gation affects the matatarsal bones and not the tarsus; but, in
these Lemurs, the caleaneum and the naviculare are prolonged,
as they are in the Frogs.

The sublingua, a process of the mucous membrane of the
floor of the mouth, developed between the apex of the tongue
and the symphysis of the mandible, acquires a considerable

390 THE ANATOMY OF VERTEBRATED ANIMALS.

size, and is often denticulated, or comblike, at its free end.
The stomach is simple, with the cardiac and pyloric apertures
approximated. The cecum is long, and has no vermiform
appendage.

In many Lemurs (Stenops, Nycticebus, Perodicticus, Arcto-
cebus, Tarsivs) the great arteries and veins of the limbs break
up into retia mirabilia formed of parallel branches.

The ventricles of the larynx may be enlarged, but there
are no great air-sacs, such as exist in many other Primates.

In the brain, the ‘cerebral hemispheres are relatively small
and flattened, and have narrow and pointed frontal lobes.
They are so short as to leave the cerebellum largely uncovered,
The gyri and sulci are scanty, or absent, upon the outer sur-
face of the hemispheres, but the internal face exhibits the cal-
carine sulcus. The large olfactory lobes project forward be-
yond the cerebral hemispheres.

The pendent penis of the male commonly contains a bone ;
' the testes are lodged in a more or less complete scrotum; and
vesiculz seminales are generally present.

In the female, the uterus has two long cornua, and the
urethra traverses the clitoris. Sometimes there are one or
two pairs of teats on the abdomen, in addition to the ordinary
pectoral pair.

The Lemuride are distinguishable into two families, the
Lemurini and the Chetromyini.

In the Lemurini, the pollex is large, opposable, and almost
always has a broad, flat nail.

6°6

. co (Died Jf 3 5°5
The usual dental formula is 7. 5. ¢. [4 p.m. M. Fz, OF He

The upper incisors are vertical, and the pairs of opposite
sides are generally separated by an interval. The upper
canines are large and pointed, and very different from the
incisors. The lower incisors are close set, laterally compressed,
long and proclivous, and the canines, which resemble them in
form and direction, are closely applied to the outer incisors,
When six grinders are present, the anterior three are premo-
lars. The anterior premolars, and sometimes all of them, have
triangular and sharp-pointed crowns; the first premolar of the
lower jaw, in fact, resembles a canine, but its true nature is
shown by its biting behind the upper canine, not in front of it.

Very generally the crowns of the upper molars are quad-
ricuspidate, and an oblique ridge passes from the antero-ex-
ternal to the postero-internal cusp, as in the highest Primates ;
while, in the lower jaw, there are either two transverse ridg es,

THE SIMIADA. 391

or longitudinal crescents. The cusps of the molars are usually
much produced, as in the Jnsectivora.

In the Cheiromyini, the pollex is not truly opposable, and
its nail is claw-like and resembles that of the other digits,
All the digits of the pes, except the hallux, have compressed,
claw-like nails. The middle digit of the manus is much more
slender than any of the others, and is longer than the fourth.
The long axis of the articular head of the mandible is antero-

osterior. The dentition di‘ers from that of all the other
Pein (and indeed from that of all the other Primates), and
resembles that of the Rodents.

Thus there is only one pair of incisors in each jaw,* and
these grow from persistent pulps and have a thick layer of
enamel on their anterior faces, whence they wear to sharp
chisel-edges, like the incisors of the Aodentia. No canines
are developed, and there are four grinders with simple crowns
on each side above and below.

The formula of the milk dentition is d.i. 5 d.c. = d.m. 4.

The Zemuride are confined to Eastern Asia, Madagascar,
and South Africa; Madagascar presenting the greatest num-
ber and diversity of genera and species.

b. In the great group of the Stmiad«, which contains the
Apes and Monkeys, the attitude is sometimes habitually quad-
rupedal, the axis of the body being horizontal; but, in a few
species, the trunk is habitually held in a more inclined posie
tion, and the animals readily assume the erect attitude.

The Simiadce are sometimes terrestrial in habit, and good
runners, but they are always excellent climbers, and, in some
cases, they are necessitated by their organization to be almost
as thoroughly arboreal as the Sloths.

The hallux is always much shorter than the second digit
of the foot, and capable of very free movement in adduction
and abduction.

The series of the teeth, in each jaw, is interrupted by a
diastema in front of the canine in the upper jaw, and behind
it, in the lower; and the canine teeth are longer than the oth-
ers, the points of their crowns projecting for a greater or less
distance beyond the rest.

In the skull, the length of the basi-cranial axis equals more
than half the extreme length of the cavity which contains the

* Among the Lemuride, the outer and upper incisors of Wycticebus and
fursius soon fall out. Lachanotus and Zarsius have only one pair of incisors
in the mandible.

892 THE ANATOMY OF VERTEBRATED ANIMALS.

brain, ‘he absolute capacity of the cranium is less than forty
cubic inches; and, if there is any difference in the length and
abundance of the hair which covers the body, it is longest on
the back. The uterus is undivided, and the clitoris is not
perforated by the urethra. The teats are only two in number,
and they are pectoral.

The Simiade are divisible into three families—the Arcto-
pithecini, the Platyrrhini, and the Catarrhini.

1. The Arctopithecini, or Marmosets, are small, thickly
furred, long-tailed, habitually quadrupedal, Squirrel-like ani-
mals, which are found only in South America. None of them
are provided with cheek-pouches, nor possess bare and callous
patches of integument over the ischia. The ears are large
and hairy, and the nose is flat and broad as in the Platyrrhini.

Fra. 110.—Skeleton of a Catarrhine Monkey (Cercopithecus).

THE ARCTOPITHECINI. 393

The fore-limhs are shorter than the hind-limbs. The pol-
.ex is not opposable, nor susceptible of extensive abduction
from the other digits, which it resembles in being provided
with a sharp, curved claw. The manus, consequently, is a
mere paw, and the term “hand” is not applicable to it.
The hallux of the foot is very small, and is provided with a
flat nail. The nails of all the other digits of the pes are fal-
cate. The plantar surface is very long, and the digits are very
short. It follows from these facts that the term “ quadruma-
nous” is not applicable, in any sense, to the Marmosets.

The skull is remarkable for the smooth and rounded sur-
face and relatively large size of the brain-case. Although the
orbits are large, the brow ridges are inconspicuous, and the
occipital region of the skull projects so far backward that the
occipital foramen may lie completely upon the under surface
of the skull, toward the junction of its middle and posterior
thirds; and have its plane almost horizontal, when the face
looks forward. The orbit is almost completely shut off from
the temporal fossa by bone.

The hyoid resembles that of the Lemurs, its body being
narrow and much arched from side to side, while the anterior
cornua are strong.

There are usually nineteen dorsc-lumbar vertebre, and the
transverse processes of the atlas are somewhat broad and flat-
tened.

. e 2°29 1—1 3°3 2-2
The dental formula is 7. 55 ¢ {5 P.M. 53 2. = = 82. Thus

the number of the teeth is the same as in man and the Catar-
rhint ; but in the number of the premolars and molars the
Arctopithecini differ from both the Catarrhini and the Platyr-
rhini, having one premolar more than the former and one true
molar fewer than the latter. In Hapale, the lower incisors
are proclivous; and the canines are approximate to them, and
similarly inclined, as in the Lemurs.

Although the manus is a paw and the pollex is not oppos-
able, this digit has its proper abductor, adductor, and long
and short flexors. The existence of a proper opponens of the
pollex is doubtful, but there is an opponens minimi digiti.
The flexor longus is completely united with the flexor profun-
dus digitorum, but the tendon for the pollex comes off on the
radial side instead of on the ulnar side, as it does in some of
the higher Simiade. The extensor secundi internodii pollicis
is united with the extensor indicts, and the extensor minimi

tgiti gives off slips to the third, fourth, and fifth digits, so that

894 THE ANATOMY OF VERTEBRATED ANIMALS.

there is a complete set of deep extensors. The four dorsal and
three palmar znterosse? are not distinctly subdivided, but they
send slips to the extensor tendons.

There are four peroncei: p. longus, p. brevis, p. quarti, and
p. quints digitt. The flexor brevis digitorum of the pes has
one division which arises from the calcaneum and goes to the
second digit ; the other three heads arise from the tendons of
the flexor perforans. The flexor accessorius furnishes almost
the whole of the long flexor tendons of the hallux, the flexor
longus digitorum supplying the perforating tendons of the
second and fifth digits; while the flexor hallucis longus gives
off the corresponding tendons of the third and fourth digits.
The énterossei, in the pes, appear to be represented only by
the pairs of muscles which act as short flexors of the basal
phalanges, and these lie altogether upon the plantar aspect of
the five metatarsal bones. The hallux has no special adductor,
nor is there any transversus pedis. In fact, the pes is almost
as completely a “ paw” as is the manus.

The brain has long and relatively large cerebral hemi-
spheres, the posterior lobes of which project far beyond the
cerebellum, and thus completely hide it, in the upper view of
the brain. The external surfaces of the hemispheres are al-
most smooth, but the Sylvian fissure is well marked, and there
is a trace of that of Rolando. On the inner face of each hemi-
sphere, the calcarine fissure is deep and gives rise to a well-
marked /Aippocampus minor within the posterior cornu of the
lateral ventricle. The corpus callosum has about a third the
length of the hemispheres. The septum lucidum is very thick,
and the precommissural fibres abundant. The vermis projects
beyond the lateral lobes of the cerebellum, and the flocculi are
large.

°. The Platyrrhini are essentially quadrupedal and planti-
orade, though some, like the Spider Monkeys (Afeles), occa-
sionally assume the erect posture. They all possess tails, and
in some genera (e. g., Aée/es) this organ becomes very flexible
and muscular, and the under surface of its extremity is devoid
of hair and highly sensitive. The tail, thus modified, is a
powerful prehensile organ, and serves as a fifth hand. The
partition between the nostrils is broad and separates them
widely, so that the nose is remarkably wide and flat, whence
the name of the group. The ears are rounded and _ bare.
There are no cheek-pouches, nor ischial callosities, in any
Platyrrhine Monkey. In most, the fore-limbs are shorter than
the hind-limbs, but the reverse is the case in the Spider Mon-

THE PLATYRRHINI. 395

«xeys. The pollex differs less from the other digits than it
does in the Catarrhini. It is more nearly parallel with, and
in the same plane as, the other digits of the manus; and,
though capable of extensive adduction and abduction, can
hardly be said to be truly opposable. The hallux is large, and
susceptible of extensive movements in abduction and adduc-
tion.

The number of the dorso-lumbar vertebree varies from
seventeen to twenty-two, the greatest number being pos-
sessed by Wyctipithecus, which has 22 (14+8 or 15+7). In
those forms which have prehensile tails the terminal caudal
vertebree are flattened from above downward. The articular
surface of the head of the humerus looks more backward than
inward ; and, not unfrequently, there is a foramen above the
inner condyle. The carpus contains nine bones. The pollex
is generally complete, but, in Ateles, it is reduced to a small
metacarpal (to which, usually, a single minute nodular phalanx
is articulated), and is completely hidden beneath the integu-
ment, The pelvis is, generally, elongated, and the anterior
ramus of the pubis lies at right angles with the long axis of
the narrow ilium. ‘The tuberosities of the ischia are everted,
but not rugose. In Afeles, the pelvis is broader, and the pubis
forms a more open angle with the ilium. The calcaneal pro-
cess is always very short, and compressed from side to side.

The brain-case is rounded and devoid of strong crests.
There is no distinct mastoid process, and the styloid is not
ossified. The coronal suture is generally V-shaped, the apex
of the frontal bone extending far back on the vertex of the
skull. The alisphenoid and the parietal bones unite upon
the side-walls of the skull. The external auditory meatus is
not ossified, the tympanic bone retaining its fcetal, hoop-like
form. The frontal bones approach one another on the floor of
the skull, but rarely unite over the junction of the presphenoid
with the ethmoid. On the inner surface of the periotic bone
there is a fossa overarched by the anterior vertical semicircular
canal, in which the flocculus rests. In Ateles the greater part
of the tentorium is ossified. In other respects, the skull pre-
sents extraordinary variations among the Platyrrhini ; the
two extremes being presented by the Howling Monkeys
(Mycetes) and the Squirrel Monkeys (Chrysothrizx). In the
former, the face is very large and prominent, with a low facial
angle. The roof of the brain-case is depressed; the plane of
the occipital foramen is almost perpendicular to the basi-era-
nial axis; and that of the tentorium is very much inclined.

396 THE ANATOMY OF VERTEBRATED ANIMALS.

The occipital condyles are, consequently, situated at the pos:
terior end of the basis cranii, and the basi-cranial axis is as
long as the cerebral cavity. In Chrysothria, on the contrary,
the face is relatively small, with a high facial angle; the brain-
case is moderately arched; the plane of the tentorium is hori-
zontal, like that of the occipital foramen, which lies but little
behind the middle of the base of the skull. The basi-cranial
axis is much shorter than the cerebral cavity. The pre-
maxillo-maxillary suture disappears early in Cebus.

The formula of the adult dentition is 7. =e. = p.m =
m. ;3—86. The crowns of the molar teeth usually have two

transverse ridges, ending in four cusps. In the upper molars
of Ateles and Mycetes an oblique ridge crosses the crown from
the antero-external to the postero-internal cusp. The pezma-
nent canines usually make their appearance before the last
molar.

The stomach is simple, the cecum large, and devoid of
any vermiform appendix; the liver is usually five-lobed; and
the kidney has a single papilla.

The ventricles of the larynx are not usually developed into
air-sacs. In Ateles, however, a median air-sac is developed
from the posterior wall of the windpipe between the cricoid
cartilage and the first ring of the trachea. A very remarkable
modification of the hyoid and larynx takes place in Mycetes.
The cornua of the hyoid are rudimentary, but its body is con-
verted into a large thin-walled bony drum, the cavity of which
communicates, beneath the large epiglottis, with that of the
larynx. The thyroid cartilage is very large, and the carti-
lages of Wrisberg and Santorini are replaced by a fibrous mass,
which is united posteriorly with its fellow of the opposite side.
In addition to the hyoidean air-sac the ventricles of the larynx
are dilated and prolonged upward, coming into contact above
the larynx; two pharyngo-laryngeal pouches may be added
to these. Mycetes is famous for the distance to which its
howling voice can be heard in the South American forests.

Although the pollex is rudimentary and apparently fune-
tionless in Afe/es, all its characteristic muscles (abductor, ad+
ductor, flecor brevis, and opponens) are present, except the
long flexor.

In Wyctipithecus the pedal interossei are flexores breves,
and lie on the plantar surfaces of the metatarsal bones, as in
the Marmosets ; but both the adductor hallucis and the trans:
versus pedis are well developed.

THE CYNOMORPHA. 397

The brain varies remarkably in different Platyrrhini. In
Chrysothrix, the cerebral hemispheres project beyond the
cerebellum to a greater relative extent than in any other Mam-
mal, namely, by one-fifth of their total length. On the other
hand, in Mycetes, the cerebral hemispheres hardly hide the
cerebellum, when the brain is viewed from above.

In Cebus, the outer surface of the brain is almost as much
convoluted as in the Catarrhine Apes. -Afeles has the external
perpendicular fissure almost obliterated by the annectent gyri,
and, so far, exhibits a higher type of brain than the Catar-
rhint ; but, in Pithecia, Chrysothrizx, and Nyctipithecus, the
external sulci gradually disappear, until the brain is almost as
smooth as in the Marmosets. On the inner faces of the hemi-
spheres, however, the internal perpendicular, the calloso-mar-
ginal, the calcarine, and the collateral sulci remain, while, in
the interior of the hemispheres, the posterior cornu and the
hippocampus minor are always present.

The vermis of the cerebellum is large and projects beyond
the level of the posterior margins of its hemispheres ; the floc-
culus is large and lodged in a fossa of the periotic ossification,
as in the Marmosets. The upper ends of the pyramids are
separated by corpora trapezoidea from the pons Varolii.

The penis is usually terminated by a large, button-shaped
glans. The cavity of the tunica vaginalis is not shut off from
the abdomen, and the testes lie at the sides of, rather than be-
hind, the penis. The female Afeles has a long clitoris, which
depends from the vagina.

The Platyrrhini occur only in the Austro-Columbian proy-
ince, and are known in the fossil state only in certain caves
of that region.

3. The Catarrhini.—The Simiade of this division present
a great range of variation in most respects, but they agree in
having the partition between the nostrils narrower than in the
Platyrrhini ; in possessing a bony meatus auditorius; in the
dental formula ¢. >> ¢. 3} pm. 5 m. == and in being in-
habitants of the Old World. They fall into two very distinct
groups, the Cynomorpha and the Anthropomorpha.

a. The Cynomorpha are distinguished from the other
group by being essentially quadrupedal, and usually provided
with a tail, which is never prehensile. The femur and tibia,
taken together, are longer than the humerus and the radius,
The outer inferior incisors are not larger than the inner ones,
but are often smaller. The crowns of the molar teeth present

398 THE ANATOMY OF VERTEBRATED ANIMALS.

two transverse ridges, a third being present, in some genera,
on the last inferior molar.

All the Cynomorpha have ischial callosities, which some-
times attain a very large size, and are brightly colored.

The dorso-lumbar region of the spinal column is concave
toward the ventral aspect, and the lumbo-sacral angle is very
large. The atlas has narrow transverse processes. ‘The or-
dinary number of dorso lumbar vertebre is nineteen, of which
twelve, or thirteen, are dorsal; and seven, or six, lumbar.
The middle cervical vertebree have short spines, which are not
bifurcated at their extremities. In the posterior dorsal and
anterior lumbar vertebrae, the mammillary and accessory pro-
cesses may be enlarged and interlock. The long transverse
processes of the lumbar vertebree bend forward. The sacrum
usually contains only three anchylosed vertebra. The caudal
vertebree vary in number, from three in Jnuus (where they
form little more than a coccyx), to as many as thirty-one. In
the anterior part of the tail the vertebrze are provided with
subvertebral, or chevron, bones.

The thorax is laterally compressed, and the manubrium of
the sternum is broad; but the six or seven sternebree which
follow it are compressed and constricted.

The skull presents a considerable range of variation. In
the Semnopithecit and Colobi, the frontal region is rounded,
the facial angle is comparatively large, and the ascending por-
tion of the ramus of the mandible is high. In the Macaci and
Cynocephali, on the other hand, the supra-orbital ridges be-
come so much enlarged as to hide the forehead; and the hori-
zontal portion of the ramus of the mandible is much larger
than the ascending portion, in accordance with the great pro-
duction of the upper jaw, and the consequent low facial angle.
In many of the Cynocephali, longitudinal osseous ridges are
developed upon the maxillz, and greatly increase the brutish-
ness of their aspect. Sagittal and lambdoidal crests may ap-
pear along the lines of the corresponding sutures. There is
no distinct mastoid process; and the styloid process is not
ossified. ‘The parietal bones do not unite with the alisphe-
noids, being separated from them by the union of the squamo-
sals with the frontals. The brain-case is flattened and elon-
gated, and the convex roofs of the orbits project into it, and
greatly diminish the capacity of its frontal portion. The olfac-
tory fossz are very deep, and sometimes almost tubular, The
two frontal bones send thick processes across the base of the
skull, which unite over the junction of the presphenoid and

THE OSTEOLOGY OF THE CYNOMORPHA. 399

the ethmoid, and thus narrow the entrance to the olfactory
fossz. The basicranial axis is shorter than the cerebral cavity,
but is still proportionally long. The occipital foramen lies in
the posterior sixth of the base of the skull, and it looks ob-
liquely backward and downward. The premaxillo-maxillary
suture never disappears until long after the second dentition
as complete, and may persist throughout life. The palate is
long and narrow. ‘The nasal bones are flat, and early anchy-
lose into one bone.

The scapula is relatively longer and narrower than that
of Man; but the spine lies at right angles to the vertebral
border, and the supra-spinous is much smaller than the infra-
spinous fossa.

The axis of the articular head of the humerus is not di-
rected upward and inward, but upward and backward; the
bicipital groove lies on the inner side; and the shaft of the
bone is so bent that it is convex forward. In all these char-
acters the fore-limb shows its relation to the function of sup-
port. The radius exhibits modifications which have the same
signification. Its proximal head is transversely elongated,
and lies somewhat in advance of the ulna, articulating more
largely with the humerus than in the higher Apes. The neck
of the radius (between the head and the bicipital tuberosity)
fits more closely to the ulna, and hence the movements of pro-
nation and supination are restricted.

There are nine bones in the carpus. The pisiforme is
much elongated, making a sort of heel for the manus. To-
gether with the cuneiforme, it furnishes an articular face for
the ulna. The distal articular surface of the trapezium is
saddle-shaped, and the pollex is usually complete, though
short relatively to the other digits. In Colobus it is rudi-
mentary.

The pelvis is long and narrow. The ilia are narrow bones
with much-excavated posterior and outer faces. Their crests
generally lie opposite the transverse processes of the penulti-
mate lumbar vertebra. The long axis of the ilium and that
of the anterior ramus of the pubis cut one another nearly at a
right angle; while the long axis of the ilium and that of the
posterior ramus of the ischium lie nearly in one straight line.
The symphysis pubis is very long, and the subpubic arch cor-
respondingly reduced. The posterior ends of the ischia are
everted, broad, and rough, for the attachment of the callous
pads of integument. The femur has a round ligament. The
tarsus has not more than one-third the length of the foot.

£00 THE ANATOMY OF VERTEBRATED ANIMALS.

The calcaneal process is flattened from side to side, and has a
pulley-like excavation upon its posterior extremity. The
tibial facet of the astragalus is inclined slightly inward, as
well as upward, and its outer edge is raised. The distal di-
vision of the tarsus, consisting of the cuboid and navicular,
with the cuneiform bones, is capable of a considerable amount
of rotatory motion upon the astragalus and the calcaneum.
The ento-cuneiform bone is large, and has a transversely-con-
vex articular surface for the metatarsal of the hallux. Conse-
quently the latter (which is skort, reaching to only about the
middle of the proximal phalanx of the second digit) is capable
of free motion in abduction and adduction.

In the Cynomorpha, and even in the so-called “ tailless ”
genus, Znwus, proper caudal muscles are present. In the limbs
there is a levator clavicule which passes from the transverse
process of the atlas to the acromion; a dorso-epitrochlearis,
consisting of a muscular bundle detached from the latissinvus
dorsi near its insertion, and passing to the distal and inner
end of the humerus, or even farther down; a scansorius, from
the ventral edge of the ilium to the great trochanter, which
sometimes becomes confounded with the glutwus minimus ; a
special abductor ossis metacarpi quinti; and a peronceus
guint digiti, arising from the fibula, between the peronceus
longus and brevis, passing behind the external malleolus, and
sending its tendon to the extensor sheath of the fifth digit.

The extensor primi internodii pollicis and the peroncus
tertius are absent in this, as in the preceding group.

The biceps femoris usually possesses only an ischial head,
and the soleus arises only from the fibula. The flexor brevis
digitorum arises partly from the tendon of the plantaris,
where this passes over the pulley on the posterior surface of
the calcaneal process to become continuous with the plantar
fascia, and partly from the tendons of the long flexor. The
transversus pedis is usually fully developed, but has only two
heads of origin from the distal ends of the second and third
metatarsals. The interossei pedis are just visible ou the dor-
sal aspect of the foot, but none are, properly speaking, dorsal.
None of them are penniform muscles arising from adjacent
sides of the metatarsal bones; but they are attached, in pairs,
to the plantar and lateral aspects of the metatarsal bones of
the digits to which they appertain. They are inserted into
the sesamoid bones, of which each digit has two, and into the
bases of the proximal phalanges, and give off no distinct ten-
dons to the extensor sheaths. Additional muscles may arise

THE DENTITION OF THE CYNOMORPHA. 401]

over the proximal ends of the metatarsal bones, and pass to
the three fibular digits.

The interossei manus are very similar to those of Man,
being divided into a dorsal and a palmar set, and sending slips
to the extensor sheaths of the digits, without that complete
subdivision which is seen in the Anthropomorpha.

There is a complete double set of extensors in the four
ulnar digits of the manus, the extensor minimi digiti giving
a tendon to the fourth digit, and the extensor indicis one to
the third digit. The extensor ossis metacarpi pollicis gives a
distinct slip to the trapezium, and thus precisely corresponds
with the tibialis anticus, which has two tendons, one for the
ento-cuneiform, and one for the metatarsal of the hallux. The
flexor digitorum profundus and jlexor longus pollicis are rep-
resented by one muscle, a slip from the ulnar side of the ten-
don of which usually goes to the pollex.

The tendons of the flexor perforans digitorum and flexor
hallucis unite to form the deep flexor tendons of the pedal
digits in very variable proportions. The flexor accessorius is
very generally present.

The anterior upper premolar has its outer cusp peculiarly
modified and sharpened. The anterior lower premolar has
the anterior margin of its crown prolonged and cutting, so
that it works like as cissors-blade, against the posterior edge
of the upper canine. In the upper jaw, the premolars have
three roots; in the lower two. The molars in both jaws have
four cusps connected by two transverse ridges. Sometimes
there is “ heel” behind the posterior ridge of the last lower
molar.

The formula of the milk dentition is d.i. 5 dc. = dim,

°2
nent premolars, while the posterior is like a permanent molar,

The permanent canines make their appearance before, or,
at latest, contemporaneously with, the hindermost molar in
both jaws. They are large and long, and are separated, by
a well-marked diastema, from the outer incisor above, and
from the first premolar below.

The Cynomorpha very generally possess cheek-pouches,
which serve as pockets for the temporary stowage of food.
The stomach is usually simple, with a globular cardiac ex-
tremity and an elongated pyloric portion; but, in Semnopithe-
cus and Colobus, the stomach is divided into three compart-
ments, the middle of which is sacculated. A groove with

= 20; and the anterior milk molar resembles the perma-

102 THE ANATOMY OF VERTEBRATED ANIMALS,

raised edges leads from the cardiac end of the gullet to the
middle compartment.

The czecum, though distinct, is relatively small, and has no
vermiform appendage.

The liver varies much in the degree of its subdivision into
lobes, being least divided in the Semnopitheci, and most in
the Baboons. The innominate artery generally gives origin
to both carotids, as well as to the right subclavian, the left
subclavian arising directly from the arch of the aorta.

When laryngeal air-sacs are developed, they are not
formed by dilatations of the lateral ventricles of the larynx,
but a single sac, with a median aperture, is formed in the
thyro-hyoidean space immediately beneath the epiglottis.
This median air-sac is very large, extending down over the
front of the neck, and sending processes into the axillze, in
some Semnopithect and Cynocephali. The right lung is usu-
ally four-lobed, the left two-lobed.

The kidney has only a single papilla.

The posterior lobes of the cerebrum project beyond the
cerebellum in all the Cynomorpha; they are shortest in the
Semnopithect, and longest in the Cynocephali. The principal
sulci and gyri which are found in the human brain are always
indicated; but the external perpendicular fissure is strongly
marked. ‘The posterior cornu of the lateral ventricle is large,
and there is a strongly-marked hippocampus minor.

There is usually, if not always, a bone in the penis, which
is provided with two special retractor muscles. The females
are subject to a periodical turgescence of the sexual organs,
sometimes accompanied by hzmorrhage, and comparable to
menstruation. The placenta is often bilobed.

b. The Anthropomorpha differ from the Cynomorpha in
the following characters: They are especially arboreal ani-
mals, which habitually assume a semi-erect posture, support-
ing the weight of the fore-part of the body upon the ends of
the fingers, or, more usually, upon the knuckles. There is no
tail, The thigh and the leg are, respectively, shorter than
the arm and the fore-arm. The dorso-lumbar vertebre are
seventeen or eighteen in number, and their spines are not in-
clined toward a common point. ‘They develop no interlocking
mammillary and accessory processes. The sacrum contains
more than three anchylosed vertebrae. The thorax is rather
broad than laterally compressed, and the sternum is flattened
from before backward, and wide. The axis of the head of the
humerus is directed more inward than backward, and the un-

THE ANTHROPOMORPHA. 403

per part of the shaft is not bent as in the Cynomorphu. The
radius is capable of complete pronation and supination.

The relative proportions of the incisor teeth are the same
as in Man; that is to say, the inner upper incisors and the
outer lower incisors are larger than the others. The crowns
of the upper and lower molars have the same patterns as those
of Man.

The caudal muscles are small or absent. When the pollex
has a flexor tendon, that tendon is nota slip given off from
one common to the flexor pollicis and flexor _perforans, as in
the Cynomorpha. The plantaris does not pass over a pulley
furnished by the calcaneal process, as in the Cynomorpha ,;
and the flexor brevis has an origin from that process. The
peronceus quintt digitt has not been observed.

There are three well-marked genera of Anthropomorpha—
Hylobates, Pithecus, and Troglodytes ; and perhaps a fourth,
Gorilla, may be advantageously separated from the last-
named.

Pithecus, the Orang, has the smallest distributional area,
being confined to the islands of Borneo and Sumatra; HHy/lo-
bates, the Gibbons, of which there are several species, is found
over a considerable area of Hastern Asia and the islands of the
Malay Archipelago. The Chimpanzee and Gorilla are met
with only in the intertropical parts of West Africa.

The Gibbons are those Anthropomorpha which are most
nearly allied to the Cynomorpha. They possess ischial cal-
losities, and the nails of the pollux and hallux, only, are broad
and flat, The arms are so long that the points of the fingers
readily touch the ground when the animal stands upright, as
it very readily and commonly does. The Gibbons also run
with great swiftness, putting the sole of the foot flat on the
ground and balancing themselves with their long arms. Ney-
ertheless, they are essentially arboreal animals, leaping from
bough to bough of the trees in the forests which they frequent
with marvellous force and precision. The manus is longer
than the pes, and the antibrachium considerably longer than
the brachium. The Gibbons do not exceed three feet in
height; their heads are small, and their bodies and limbs
remarkably slender.

None of the other Anthropomorpha have callosities, and
the nails of all the digits are flattened. They are all heavier
_in make, with proportionally shorter limbs and larger heads
than the Gibbons. In the Orangs, which rarely attain a state
ure of more than four feet and a half, the arms are very long,

404 THE ANATOMY OF VERTEBRATED ANIMALS.

their span, when outstretched, being nearly double the height
of the animal. The brachium and the antibrachium are equa!
in length. The long and narrow pes is longer than the equal-
ly narrow manus, and the sole cannot be placed flat upon the
ground, but the animal rests upon the outer edge of the foot
when it assumes the erect posture. This posture, however, is
quite unnatural, and the Orangs cannot run as the Gibbons
do, but swing themselves along upon their long arms, as it
were upon crutches.

The pollex and the hallux are both short, the latter remark-
ably so; and the hallux is not uncommonly devoid of a nail.
The palmar and plantar aspects of the digits are naturally con-
cave, and they cannot be completely straightened.

The Chimpanzee attains a stature somewhat greater than
that of the average Orang. The span of the arms is about
half as much again as the height. The antibrachium is about
as long as the brachium. The manus is equal to, or a little
longer than, the pes; and these parts of the limbs are not so
elongated, or so curved, as the corresponding parts of the
Orang. The sole can be readily placed flat upon the ground,
and the Chimpanzee easily stands or runs erect. But his fa-
vorite attitude is leaning forward and supporting himself on
the knuckles of the manus. Both the hallux and the pollex
are well developed and possess nails.

The Gorilla exceeds five feet in height and may reach five
feet six inches. The span is to the height as about three to
two. The brachium is much longer than the antibrachium.
The pes is longer than the manus, and both are much
broader than in the other Anthropomorpha. In consequence
of this circumstance and of the greater development of the
heel, the erect posture is easily maintained, but the ordinary
attitude is the same as that assumed by the Chimpanzee. The
hallux and the pollex have well-developed nails. The basal
phalanges of the three middle digits of the foot are bound
together by the intezument.

With respect to the skeleton in the Anthropomorpha, the
Gibbons have the spinal column nearly straight, with a very
open vertebro-sacral angle. In the Orangs the dorso-lumbar
vetebrze form a curve, which is nearly as much concave for-
ward as in a new-born child. In the Chimpanzee the spinal
column begins to exhibit the curvatures which are character-
istic of the adult human subject; and these are still more
marked in the Gorilla.

The spinous process of the second cervical vertebra is

THE ANTHROPOMORPHA. 405

bifurcated in the Chimpanzee, but this human character does
not appear in the others.

In the Gibbons there are usually eighteen dorso-lumbar
vertebra ; but in the other Anthropomorpha the number is
' ordinarily seventeen, as in Man, or may be reduced to sixteen.
The Orang has the human number of twelve pairs of ribs ;
but the Chimpanzee and Gorilla have thirteen, and the Gib-
bons may possess fourteen pairs of ribs. The thorax is wide,
and the sternum broad and flat. In the Orang it may ossify
from a double longitudinal series of centres, as sometimes hap-
pens in Man.

In the Gibbons the transverse processes of the last lumbar

vertebra are not exceptionally broad, and do not unite with
the ilia. But in both the Chimpanzee and Gorilla they are
wide, and become more or less closely connected with the ilia.
The last lumbar vertebra may become anchylosed with the
sacrum in the Gorilla. All these conditions of the last lum-
bar vertebra are occasionally met with in Man.
_ The sacrum is broad, and contains not fewer than five
anchylosed vertebra, but its length always exceeds its breadth
(whereas its breadth is equal to, or exceeds, its length, in Man),
and its anterior curvature is but slight. The short coccyx is
made up of not more than four or five vertebra. In the skull,
the proper form of the brain-case is always more or less, dis-
guised in the adult males, by the development of crests for
muscular attachment, or of the orbits and the supraorbital
ridges. In the Gibbons and Chimpanzees, the latter are
large, but the sagittal crest is absent, and the lambdoidal
small, In the Orang, the brow-ridges are small, so that the
true form of the forehead is seen better than in the other
Apes, but the sagittal and lambdoidal crests are strong. In
the old male Gorilla the sagittal and lambdoidal crests, and
the supraorbital ridges, are alike enormous. ‘The frontal si-
nuses are large, and extend into the brow-ridges both in the
Gorilla and Chimpanzee. The jaws are largest in proportion
to the brain-case in the Gorilla and the Orang; smallest in
some varieties of Chimpanzee.

In all the Anthropomorpha the transverse is much less
than the longitudinal diameter of the cranial cavity. The
roofs of the orbits project into the frontal portion of the brain-
case, and diminish its capacity by causing its floor to slope
from the middle line obliquely upward and outward. The oc-
cipital foramen is situated in the posterior third of the base
of the skull, and looks obliquely backward and downward.

406 THE ANATOMY OF VERTEBRATED ANIMALS.

The frontals meet in the base of the skull over the ethmo-
presphenoidal suture in the Gibbons and in the Gorilla, as in
the Baboons; but not in the Chimpanzee or the Orang. The
alisphenoids unite suturally with the parietals, as is the rule
in Man, in the Gibbons and (usually) in the Orangs; but, in ©
the Chimpanzee, the squamosal unites with the frontal and
separates the alisphenoid from the parietal, as happens, excep-
tionally, in Man. The nasal bones are flat and early anchylosed
together, in the Gibbons, Orangs, and Chimpanzees. In the
Gorilla the nasal bones are distinetly convex from side to side,
and rise above the level of the face. None of these Apes havea
spina nasalis anterior ; and, only in the Siamang, is there a
rudiment of the mental prominence in the mandible. The
premaxillo-maxillary suture persists beyond the completion of
the second dentition in all but the Chimpanzee, in which it
disappears before that period. The epiotic region is never
developed into a distinct mastoid process; and there is an os-
sified styloid process only occasionally in the Orangs. The
palate is long and narrow, the alveolar margins being nearly
parallel, or even diverging anteriorly. The ; zyaomatic arches
are strong, wide, and curv ved in two directions,

The proportion of the length of the basi-cranial axis to
that of the cerebral cavity does not fall lower than the ratio
of 19 to 17 in any of the Anthropomorpha.

The body of the hyoid approaches the form of that of Man
most nearly in the Orang. In the other genera itis more ex-
cavated posteriorly.

The scapula of the Orang is most like that of Man, espe-
cially in the proportion of the supra- and infra-spinous fossa,
in the proportional length of the anterior and the posterior
borders, and in the angle made by the spine with the verte-
bral margin. In the other genera the posterior border is
longer in proportion than in Man, and the spine of the scapula
cuts the vertebral margin more obliquely. After the Orang’s,
the scapula of the Gorilla comes nearest to that of Man.

On the other hand, the long and straight clavicle of the
Orang is least like that of Man.

The head of the humerus loses the backward inclination
which it has in the lower Apes, and becomes directed up-

ward and inward, asin Man. ‘The radius and ulna are curved,
and leave a wide interosseous space. ‘There are nine bones
in the carpus in both Aylobates and Pithecus, but only eight
in the Chimpanzee and Gorilla. In Hylobates the articular
surface presented by the trapezium for the pollex is almost

THE FOOT IN THE ANTHROPOMORPHA. 407

globular. It is evenly convex in the Chimpanzee; but, in the
Gorilla, it has the characteristically human saddle shape. The
pollex is longest and strongest in proportion in LHylobates ;
its length in proportion to that of the manus being in ZZ. syn-
dactylus as three to seven. In the Gorilla, the pollex has
rather more than one-third the length of the manus; in the
Orang and Chimpanzee it has about one-third the length of
the manus.

The pelvis differs but little from that of the Cynomorpha
in Hylobates. In the other genera the pelvis is still elongated.
The antero-posterior diameter of the brim of the pelvis great-
ly exceeds the transverse, the tuberosities of the ischia are
strongly everted, and the pubic symphysis is very long, the
arch being correspondingly reduced; but the ilia are wider
and more concave forward in the Chimpanzee than in the
Orang, and in the Gorilla than in either.

In the female Chimpanzee, which is of about the same size
as the male, the dimensions of the basin of the pelvis, and of
its outlets, are greater than in the male, though the general
form and absolute length of the pelvis are the same in the two
sexes. The female Gorilla is much smaller than the male, and
the pelvis is shorter in proportion, but the intersciatic meas-
urement of the outlet is absolutely as great as in the male,
and the transverse diameter of the brim is nearly as great.
As, at the same time, the antero-posterior diameter is much
shorter, the brim of the pelvis of the female is much more
round, The female Orangs, also, are smaller than the males.
The basin of the pelvis is relatively, but not absolutely, larger
in all its dimensions, and the brim rounder.

The femur of the Orang has no round ligament, and differs
in this respect from the same bone in the other Anthropomor-
pha. The femur of the Gorilla resembles that of Man, most
especially in the projection of the articular surface of the inner
condyle beyond the outer.

The length of the whole foot to that of the tarsus is, in
Hylobates, as thirty-five to ten, and the proportion is about
the same in the Orang; in the Chimpanzee it is as twenty:
four to ten; and, in the Gorilla, about the same (twenty-three
to ten in the specimen measured).

The hallux has not more than one-fourth of the length of
the foot in the Orang; in the Gorilla less than five-twell{ths ;
in the Chimpanzee and in Hylobates a little more.

In the second digit of the pes of the Orang and the Chim-
panzee, the phalanges, taken together, are longer than the

408 THE ANATOMY OF VERTEBRATED ANIMALS.

metatarsal bone of the digit; in the Gorilla, they are about
equal in length to the metatarsal. The calcaneal process is
longest, strongest, and broadest, in the Gorilla. In the astrag-
alus the articular surface for the tibia is broadest in the Goril-
la; but, in this Ape, as in the others, it is inclined a little in-
ward when the foot is in its natural position; and the surface
for the external malleolus is oblique, and looks upward as well
as outward.

It is a mistake, however, to suppose that the disposition
of these surfaces has any thing to do with the more or less
marked tendency of the plantar surface to turn inward, and
of the outer edge of the pes to be directed downward, which
is observable in all the Anthropomorpha. 'This tendency is
the result of the free articulation between the scaphoid and
the cuboid, on the one hand, and the astragalus and the calca-
neum on the other; the consequence of which is, that the dis-
tal portion of the pes, with the first-mentioned bone, being
pulled by the tibialis anticus, easily rotates round its own
axis, upon the surface presented by the astragalus and calca-
neum. ‘This ready inversion of the sole must as much facili-
tate climbing, as it must interfere with the steadiness of the
foot in walking.

The distal surface of the ento-cuneiform is much inclined
inward in all the Anthropomorpha, and is convex from side to
side, or subcylindrical. The metatarsal bone of the hallux pre-
sents a corresponding articular concavity to this surface, and
has a great range of motion in adduction and abduction. The
inward inclination of the articular facet of the ento-cuneiform,
and its consequent separation from the facet upon the meso-
cuneiform for the second digit, is greatest in the Orang, in
which the hallux is habitually directed at right angles to the
long axis of the foot. The distal phalanx of the hallux is not
unfrequently absent in the Orang.

All the Anthropomorpha possess certain muscles which
are not usually found in Man, though they may occur as vari-
eties in the human subject. These are the levator clavicule,
the dorso-epitrochlearis, the scansorius,* and the abductor
ossis metacarpt quinti digiti. They are also devoid of two
muscles which are usually present in Man—the extensor primi
internodii pollicis + and the peroneus tertius. 'The former of

* Not actually described in the Gorilla, and absent in some Chimpanzees.

+ The former muscle is said to be present by several anatomists in the
Chimpanzee and other Apes; but what they have taken for it is the metacar-
pal division of the extensor ossis metacarpi.

THE MYOLOGY OF THE ANTHROPOMORPHA. 409

these is sometimes, and the latter frequently, wanting in the
human subject.

The flexor accessorius appears to be regularly absent in
Hylobates and Pithecus, and, in the majority of cases, in the
Chimpanzee. The transversus pedis seems to be absent in the
Orang, but it is present in the other Anthropomorpha. ee

Many muscles which exist both in these Apes and in Man
have different origins in the former. Thus, the soleus has
only a fibular head, and takes no origin from the tibia. The
fiexor brevis digitorum pedis never arises altogether from the
calcaneum, but a large proportion of its fibres spring from the
tendons of the deep flexors. The calcaneal head furnishes the
tendons for the second, or the second and third, digits. - The
interosseous muscle which lies on the tibial side of the middle
digit of the pes, usually arises from the fibular side of the sec-
ond metatarsal as well as from the tibial side of its own meta-
tarsal, and its origin lies on the dorsal side of that of the fibu-
lar interosseous muscle of the second digit. Hence, of the so-
called dorsal interosset interosset which are visible on the
dorsal aspect of the pes) two belong to the middle digit, and
one, to the second and fourth digits respectively ; which is
the same arrangement as that which obtains in the manus.
The flexor pollicis is more or less closely connected with the
flexor communis perforans, or with that part of the muscle
which goes to the index digit. The connection is slightest in
Hylobates, the origins of the two muscles, only, being united.
It is most extensive in the Orang, in which no tendon goes to
the pollex. The same complete loss of the flexor pollicis, as
a thumb-muscle, occasionally takes place in the Gorilla; but
in this animal, as in the Chimpanzee, the rule appears to be,
that the flexor pollicis unites at its origin with part of the
Jlexor perforans, and that the fleshy fibres converge to a com-
mon tendon which divides into two, one for the pollex and
the other for the index. In AHylobates, the short head of the
biceps brachii arises from the pectoralis major, and the ad-
ductor hallucis and transversus pedis form but one muscle.

The flexor longus hallucis takes an origin from the ex-
ternal condyle of the femur in the Orang; and the pectoralis
major arises by three distinct slips.

Some of the muscles in the Anthropomorpha differ in
their insertion, or in the extent to which they are subdivided,
from what is usual in the corresponding muscles of Man.
Thus the extensor ossis metacarpi pollicis ends in two distinct
tendons: one for the trapezium, and the other for the base of

i8

410 THE ANATOMY OF VERTEBRATED ANIMALS.

the metacarpal bone of the pollex. That part of the tibialis
anticus which goes to the metatarsal of the hallux is usually
very distinct, and is sometimes reckoned as a separate muscle,
the abductor longus hallucis.

In the Gibbons and in the Orang, there is a complete set
of deep extensors for the four ulnar digits, the tendons of the
extensor indicis and extensor minimt digitt subdividing to
supply the third and fourth digits. ;

In the Gorilla and Chimpanzee each of these muscles have
but a single tendon, as is the usual arrangement in Man,

The interossei of the hand are each divided into two mus-
cles with distinct tendons—a flexor brevis primi internodii and
an extensor brevis tertit internodii. 'The division is less obvi-
ous in the Orang than in the other Anthropomorpha.

In Hylobates, the tendon of the flecor perforans pedis goes
only to the fifth digit, and is not directly connected with that
of the flexor longus hailucis, which supplies the other four
digits. In the Orang, also, the tendons of the two muscles are
separate ; but the flewor perforans supplies the second and the
fifth digits, and the flexor hallucis the third and fourth. It
gives no tendon to the hallux. In both the Chimpanzee and
the Gorilla, a very large tendon is given to the hallux by the
fiexor hallucis, and it also supplies the third and fourth digits,
The tendon of flexor longus digitorum is but slightly con-
nected with that of the flexor hallucis, and its divisions go to
the second and fifth toes. In both the manus and the pes of
Hylobates a muscle occurs which is not, at present, known in
any other Mammal. It arises from the second metacarpal or
metatarsal bone, and is inserted by a long tendon into the pre-
axial side of the ungual phalanx of the second digit; it may
be termed “ abductor tertii internodii secundi digiti.”

The Orang, in like manner, stands alone in possessing a
small but distinct opponens hallucis.*

The volume of the brain, in the Orang and in the Chim-
panzee, is about twenty-six or twenty-seven cubic inches; or
about half the minimum size of a normal human brain. In the
Gorilla, the volume rises to near thirty-five cubic inches. In
the Gibbons the brain is very much smaller; and the Siamang,
among these, is remarkable for the short posterior lobes of the

* Tt must be borne in mind that these statements respecting the myology
of the Anthropomorpha are based upon my own dissections (sometimes sup-
plemented by those of Duvernoy and other anatomists) of particular speci-
mens. Endless varieties will no doubt be met with by those who carry their
inquiries further.

THE BRAIN IN THE ANTHROPOMORPHA. 411

cerebrum, which, in this anthropomorphous Ape, do not over-
lap the cerebellum as they do in all the others,

The cerebral hemispheres are higher in proportion to their
length in the Orang than in the other Anthropomorpha ; but,
in all, they are elongated and depressed, as compared with
those of Man. The frontal lobes taper off anteriorly, and their
inferior surfaces are excavated from without downward and
inward, in correspondence with the projection of the upwardly
convex roofs of the orbits into the cranial cavity. The pos-
terior cornu of the lateral ventricle is always well developed,
and contains a prominent hippocampus minor and eminentia
collateralis. An occipito-temporal or “external perpendicu-
lar” sulcus is always present. It is most nearly obliterated in
the Orangs. All the gyri of the human brain are represented
in the cerebral hemispheres of the Chimpanzee ; but they are
simpler and more symmetrical, and larger in proportion to the
brain (see Figs. 21 and 22). The fissure of Sylvius is less in-
clined backward, and that of Rolando is placed more forward
than in Man. The insula has simpler and fewer radiating sulci,
and is not completely hidden by the temporal lobe. Only the
second, third, and fourth annectent gyri appear upon the sur-
face. ‘The first remains folded upon itself, and gives rise to
the characteristically simian occipito-temporal or external per-
pendicular sulcus. The occipito-parietal sulcus, on the inner
face of the hemisphere, is much more nearly perpendicular
than in the human brain. The corpus callosum is relatively
smaller; the septum lucidum is very thick, and the precom-
missural fibres are well developed. The vermis is small in
proportion to the lateral lobes of the cerebellum, ard the floc-
culi are relatively small, and lie below the latter.

The whole cerebellum is larger in proportion to the cere-
bral hemispheres; the latter being to the former, as 84 to 1 in
Man, but as 52 to 1 in the Chimpanzee.* The nerves are
larger in proportion to the brain than in Man. There are no
corpora trapezoidea, such as exist in the lower Mammals, and
the corpora albicantia are double.

In all the Anthropomorpha, the inner incisors are larger
than the outer, in the upper jaw; smaller in the lower jaw.
There is a diastema, though it is often but small in the female
Chimpanzees. The canines are large and strong, and may be
grooved longitudinally on their inner sides. The premolars

* It must be recollected that the brains of young anthropomorphous
Apes, only, have been examined. Perhaps this has to do with the absence of
mineral deposits in the pineal gland of the Apes.

412 THE ANATOMY OF VERTEBRATED ANIMALS.

have three roots in the upper jaw, two in the lower. The
crowns of the middle molars, above, have four cusps, and an
oblique ridge which extends from the antero-external to the
postero-internal cusp; and those of the middle molar, below,
have five cusps, as in Man. The crown of the anterior premo-
lar in the lower jaw is pointed, and has a long, sharp, ob-
lique anterior edge as in the Cynomorpha.

In the Gibbons, the permanent canine emerges contem-
poraneously with, or before, the last molar; but, in the other
Anthropomorpha, the last permanent canine is cut, ordinarily,
only after the appearance of the last molar.

In the Orang the circumvallate papille of the tongue are
arranged ina V,asin Man. In the Chimpanzee they are dis-
posed like a T, with the top turned forward. The Chimpanzee
and the Siamang have a uvula, but the Orang has none.
The stomach of the Chimpanzee is very like that of Man; but
in the Orang the organ is more elongated, with a round car-
diac and more tubular pyloric portion. An appendia vermi-
Jormis is found in the czcum of all four genera. In the
Chimpanzee and Gorilla, the origin of the great arteries from
the arch of the aorta takes place asin Man. In the Orang,
they are sometimes disposed as in Man; while in other speci-
mens the left carotid comes off from the innominata, and only
the subclavian of the left side arises directly from the aorta.
In Hylobates, the latter arrangement appears to obtain.

The kidney has only a single papilla in Hylobates and
Pithecus.

Only one species of Hylobates, namely, the Siamang, is
known to possess a laryngeal sac. This is globular, and com-
municates by two apertures, situated in the thyro-hyoid mem-
brane, with the larynx. In the Orang, Chimpanzee, and Go-
rilla, enormous air-sacs result from the dilatation of the lateral
ventricles of the larynx. These dilatations extend down, in
front of the throat, on to the thorax and even into the axilla,
and sometimes open into one another in the middle line.

In the adult male Chimpanzee the penis is small and slen-
der, and terminates in a narrow and elongated glans. The
testes are very large, and the communication between the
tunica vaginalis and the peritonzum is completely closed.
The glans penis of the Gorilla is button-shaped. In the
Orang it is cylindrical, and the testes are situated close to the
inguinal canal, which has been found open on one side, and
closed on the other. An os penis is developed in the males.

The females have the clitoris large, and the uterus, which

RELATIONS OF ANTHROPOMORPHA TO MAN. 413

is undivided into cornua, resembles that of the human subject.
The placenta of a Chimpanzee foetus, 113 inches long, was sim-
ple, rounded, 3} inches in diameter, and 0.6 inch thick in the
centre. The umbilical cord was inserted near one of its edges.

The proportions of the limbs to one another and to the
body do not sensibly change after birth; but the body, limbs,
and jaws, enlarge to a much greater extent than the brain-case.

The amount of variation in the characters of the skull
among the Chimpanzees, Gorillas, and Orangs, is exceedingly
remarkable, especially if taken in connection with their very
limited areas of distribution.

Of the four genera of the Anthropomorpha, the Gibbons
are obviously most remote from Man, and nearest to the Cy-
nopithecini.

The Orangs come nearest to Man in the number of the
ribs, the form of the cerebral hemispheres, the diminution of
the occipito-temporal sulcus of the brain, and the ossified
styloid process; but they differ from him much more widely
in other respects, and especially in the limbs, than the Gorilla
and the Chimpanzee do,

The Chimpanzee approaches Man most closely in the char-
acter of its cranium, its dentition, and the proportional size
of the arms.

The Gorilla, on the other hand, is more Man-like in the
proportions of the leg to the body, and of the foot to the
hand; further, in the size of the heel, the curvature of the
spine, the form of the pelvis, and the absolute capacity of the
cranium,

c. The Anthropide are represented by the single genus
and species, Man, and they are distinguished from the
Simiade, and especially the Anthropomorpha, by the follow-
ing characters:

In progression on the ground, the erect posture is the
easiest, and no assistance is given by the arms, which are
shorter than the legs. After birth, the proportions of the body
alter in consequence of the legs growing faster than the rest
of the body. In consequence, the middle point of the height
of the body—which, at birth, is situated about the umbilicus
—becomes gradually lower, until, in the adult male, it is as
low as the symphysis pubis,

In the manus, the pollex is strong and long, reaching to
the middle of the basal phalanx of the index digit. In the
pes, the tarsus takes up half the length of the foot; the cal-
caneal process is long, and expanded posteriorly. The hallux

414 THE ANATOMY OF VERTEBRATED ANIMALS.

has half the length of the foot, and is nearly as long as the
second digit; and its mobility in adduction and abduction is
slight, compared with that of the hallux of the other Primates.

Hair is more abundant upon the crown of the head; and,
usually, in the axille, the pubic region, and the front part of
the thorax, than elsewhere.

In the new-born infant the whole dorso-lumbar region of
the spine is concave forward, and the vertebro-sacral angulas
tion is slight; but, in the adult, the spinal column is concave
forward in the thoracic, and convex forward in the lumbar.
region, mainly in consequence of the disposition of the elastic
ligaments which connect the faces and the arches of the ver-
tebre. There is a strongly-marked vertebro-sacral angulation.
Normally, there are twelve dorsal, five lumbar, five sacral, and
four coccygeal vertebre, and the transverse processes of the
last lumbar vertebra are not expanded or directly connected
with the ilia; but, in these respects, variations occur.

The spinous processes of the middle cervical vertebree are
much shorter than the seventh, and are usually bifurcated.
The breadth of the sacrum is greater than its length. In the
skull, the occipital condyles lie within the middle fifth of the
base, and the occipital foramen looks downward, and either a
little forward or but slightly backward. Neither sagittal nor
lambdoidal crests are developed, but the mastoid processes
are distinct, and generally conspicuous. The supraorbital
ridges are never so largely developed as in some of the An
thropomorpha. The orbits and the jaws are relatively smaller,
and situated less in front of, and more below, the fore-part of
the brain-case. A spina nasalis anterior is almost always
present ; * and, in the profile view of the face, the nasal bones
project more beyond the level of the ascending process of the
maxilla than they doin any Ape. The palate is broader and
its contour more arched than in any of the Anthropomorpha.
Its posterior margin is ordinarily produced in the middle line
into a spina nasalis posterior, and the palato-maxillary suture
is directed transversely.

The distance between the zygomata is either less than the
greatest transverse diameter of the calvaria, or exceeds it but
little. The malar is deeper than the squamosal portion of
the zygoma, and the upper edge of the zygoma is but little
curved.

* The only human skull in which I have been able to find no trace of the

existence of the anterior nasal spine, is that of an Australian, which, some
years ago, I presented to the Museum of the Royal College of Surgeons.

THE ANTHROPIDZA. 415

The post-glenoidal process of the squamosal is small, while
the auditory foramen is vertically elongated, its anterior wall
being more or less flattened.

The interorbital space occupies about one-fourth of the
interval between the outer walls of the orbits.

The planes of the orbital surfaces of the ethmoid bones
(ossa plana) are nearly parallel with one another.

The symphysis of the lower jaw has a mental prominence,
The length of the cerebral cavity is more than twice that of
the basi-cranial axis.

After birth, no trace of the premaxillo-maxillary suture
remains upon the face, though it may persist in the palate.

The nasal suture usually persists, and the direction of the
fronto-nasal suture is nearly transverse.

The cranio-facial angle * does not exceed 120°, and in the
higher races of mankind does not go much beyond 90°.

The supra-orbital plates of the frontal bones project but
little into the frontal region of the brain-case, and they are
almost horizontal, instead of being strongly inclined upward
and outward, as they are in the Anthropomorpha. The cri-
briform plate is long and wide, and the crista galli is usually
prominent. The capacity of the brain-case of a healthy adult is
invariably more than forty cubic inches, and may rise to more
than a hundred cubic inches.

The scapula is broad in proportion to its length, and its
spine cuts its vertebral edge nearly at right angles. © The ilia
are very broad; their inner faces present a well-marked con-
cavity, and their crests an S-shaped curvature. A line drawn
from the centre of the articular surface of the sacrum to the
centre of the acetabulum makes nearly a right angle with the
chord of the arc offered by the anterior face of the sacrum.
In all the Anthropomorpha this angle is much more open.

The tuberosities of the ischia are hardly everted. The
“symphysis pubis is comparatively short, and the sub-pubic arch
well marked. The width of the whole pelvis, from one iliac
crest to the other, is greater than its height, which is the re-
verse of what obtains in the Apes. The transverse diameter
of the brim is usually not exceeded by the antero-posterior
diameter, though the contrary proportion occasionally obtains.
The female pelvis is more spacious, and has a wider sub-pubic
arch than the male.

The proximal articular surface of the astragalus looks
almost directly upward, and hardly at all inward, when the

* See p. 420 for the explanation of this term,

416 THE ANATOMY OF VERTEBRATED ANIMALS.

sole is flat upon the ground; and the lateral facets are more
nearly at right angles to this surface than in any Ape. The
inner and outer malleoli are stronger and more downwardly
produced. The calcaneal process is thick, strong, enlarged at
its hinder end, and not incurved inferiorly, but produced into
two tuberosities on which the heel rests. The form and dis-
position of the astragalar, navicular, and calcaneo-cuboid
articulations are such that the distal moiety of the tarsus is
capable of only a slight rotatory motion upon the proximal
portion.

The distal articular surface of the ento-cuneiform bone is
very nearly flat, though it has a slight convexity from side to
side, and is irregularly concavo-convex, from above downward.
The comparatively slight mobility of the metatarsal bone of
the hallux arises partly from this circumstance, partly from
the fact that the proximal articular surfaces of the four outer
metatarsal bones are not perpendicular to the axis of those
bones, but are obliquely truncated, from the tibial side, back-
ward, to the fibular side. Hence the four outer metatarsal .
bones, instead of diverging widely from the hallux as they
would do if their axis were perpendicular to the distal facets
of the meso- and ento-cuneiform and cuboid bones, take a direc-
tion more nearly parallel with the metatarsal of the hallux,
and the base of the second metatarsal, as it were, blocks the
latter, in adduction. The hallux thus loses most of its pre-
hensile functions; but, in exchange, it plays an important
part in supporting the weight of the body, which, in the erect
position, falls on three parts of the pes; namely, the heel, the
outer edge, and the integumentary pad which stretches be-
neath the metatarso-phalangeal articulations, from the hallux
to the fifth digit.

In the infant, the sole naturally turns inward, and the
digits (especially the hallux) retain much of their mobility.

The only muscles which exist in Man, but have not yet
been found in any Ape, are the extensor primi internodi pol-
licis and the peroncus tertius.

The only peculiarities in the origin of muscles which ordi-
narily obtain in Man, and have not yet been found in the Apes,
are—the complete separation of the flexor pollicis longus from
the flexor digitorum perforans ; the presence of a tibial, as well
as of a fibular, origin of the soleus ; the origin of all four heads
of the flexor brevis digitorum pedis from the calcaneum; the
origin of the fibula dnterosseus of the second digit of the pes
from the middle metatarsal, on the dorsal side of the tibial

THE BRAIN OF MAN. 417

interosseus of the middle digit. The result of the last-men-
tioned arrangement is that the second digit of the pes has
two “ dorsal ” interossei, like the third digit of the manus. In
the Apes the interossei of the second digit are generally ar-
ranged in the same way in both manus and pes.

The tendons of the flexor hallucis longus and flexor digi-
torum perforans are usually more closely connected in the
sole of the foot in Man, than in the Anthropomorpha. But
it is to be noted that all the apparently distinctive peculiari-
ties of the myology of the Anthropomorpha are to be met
with, occasionally, as varieties in Man.

In the brain of Man, the only distinctive features, apart
from its absolute size (55 to 115 cubic inches), are the filling
up of the occipito-temporal fissure ; the greater complexity
and less symmetry of the other sulci and gyri; the less exca-
vation of the orbital face of the frontal lobe; and the larger
size of the cerebral hemispheres, as compared with the cere-
bellum and the cerebral nerves.

There is no diastema, though the summits of the canines
project, slightly, beyond the level of the other teeth. The
premolars have not more than two roots, and the anterior edge
of the crown of the anterior lower premolar is not prolonged
and sharp. The permanent canine tooth emerges before the
second molar.

The penis is devoid of a bone (though a prismatic carti-
laginous body has occasionally been found in the centre of the
glans), and its glans has a different shape from that of any of
the Anthropomorpha. The vulva looks downward and for-
ward, and the clitoris is comparatively small.

The changes in the proportions of the different parts of the
body, at different periods of intra- and extra-uterine life, are
very remarkable. In a foetus an inch and a half long, from the
vertex to the heel, the head takes up from one-third to one-
fourth of the entire length. The arms and legs are of about
the same length, and are shorter than the spine. The forearm
is about as long as the upper arm, and the leg as the thigh.
The manus and pes are very similar in size and form; and
neither pollex, nor hallux, are so different from the other digits
as at later periods. In a foetus rather more than five inches
high, the head occupies a fourth of the entire height; the
arms are longer than the spine by one-sixth of their whole
length, and are a little longer than the legs. The forearm is
about as long as the upper arm, and the thigh is a little longer
than the leg. The manus and pes are about equal in length

418 THE ANATOMY OF VERTEBRATED ANIMALS.

In a foetus eight and a half inches high, the head measures less
than a fourth of the whole height; the arms are longer than
the spine by a fourth of their whole length, and they are longer
than the legs, The extremities of the digits reach down to
the knee when the body is erect.

At full term, the height of the head of the human foetus
is rather less than a fourth that of the whole body, and the
legs are longer than the arms. The arm is longer than the
forearm and the thigh than the leg. The hands and the feet
are still about equal in length.

Thus it would appear that, while the head grows more
slowly than the rest of the body, throughout the period of ges-
tation, after the embryo has attained more than two inches in
length; the arms grow proportionally quicker than the body
and legs, in the middle of gestation, when the proportions
most nearly resemble those of the Anthropomorpha. In the
latter part of the period of gestation the legs gain on the arms,
and the proximal segments of the limbs on the distal ones.
After birth these changes are continued. The adult has, on
the average, three and a half times the height of the new-born
child, and his arms are elongated in the same proportion.
But the head is only twice as large, while the legs of the adult
are five times as long as those of the child. At all ages after
birth, the distance between the extremities of the digits of
the outstretched arms is equal to the height in average Eu-
ropeans.

Sexual differences, independent of the genitalia, are per-
ceptible at birth; and the female infant is, as a rule, slightly
smaller than the male. These differences become more marked
at, and subsequent to, puberty; and are seen in the smaller
stature of the female, the larger size of the head in proportion
to the stature, the shorter thorax, the longer abdomen, and the
shorter legs; so that the middle point of the stature of the fe-
male is nearer the umbilicus than in the male. The hips are
wider in proportion to the shoulders, whence the femora are
more oblique. The ridges and muscular processes of all the
bones are less marked, and the frontal contour of the skull is
more sharply angulated. When the peculiarities of the female
sex are not connected with reproduction, they may be said to
be infantile.

The different persistent modifications or “ races” of man-
kind present a very considerable amount of variation in their
anatomical characteristics. The color of the skin varies from
a very pale reddish brown—of the so-called “ white” races—

anit i ei

THE RANGE OF VARIATION IN ANTHROPIDZ. 419

through all shades of yellow and red browns, to olive and
- chocolate, which may be so dark as to look black.

The hair differs much in its character, having sometimes a
circular, sometimes an oval or flattened transverse section, and
presenting all varieties, from extreme length and straightness
to short, crisp wool.

The hair on the scalp is longer than that elsewhere; and
it is very often, but not always, longer in the female. Hair
upon the face and body is scanty in most races, and almost
absent, except in the eyebrows, in some; but in others it be-,
comes greatly developed over the lips, chin, and sides of the
face, on the thorax, abdomen, and pubes, in the axilla, and
sometimes, though more rarely, upon the rest of the body and
limbs. When hair is developed upon the limbs the points of
the hairs of the arm and forearm slope toward the elbow, and
those of the leg and thigh away from the knee, as in the An-
thropomorpha.

Enormous accumulations of fat take place upon the but-
tocks of the Bosjesmen, especially in the females; and the
nymphe of these and some other Negroid tribes become great-
ly elongated.

It appears in some of the lower races, e. g., Negroes ard
Australians, the forearm and hand, and the foot and leg, are
often longer in proportion than in Europeans. From not
wearing shoes, the hallux is much more movable in these
races, and the foot is commonly employed for prehension.

There is no proof of what is so commonly asserted, that
the heel is longer, in proportion to the foot in Negroes.

The spines of the middle cervical vertebrze sometimes
cease, more or less completely, to be bifurcated in the lower
races. ‘Thirteen pair of ribs are sometimes present, and occa-
sionally there is a sixth lumbar vertebra. There may be one
more sacral vertebra than the normal number; and a modifi-
cation of the last lumbar, so that it resembles a sacral verte-
bra, and becomes connected with the ilia, seems to be more
common in Australians and Bushmen than in other stocks.

In the lower races, the male pelvis is less in many of its
dimensions, and seems to differ more from the female, espe-
cially in the tendency to equality of the transverse and antero-
posterior diameters of the brim, and the narrowness of the in-
tersciatic diameter, than in the higher races, ‘This is particu-
larly obvious among the Australians. The antero-posterior
diameter of the brim of the pelvis is occasionally greater
than the transverse, and this variety would seem to be com:

420 THE ANATOMY OF VERTEBRATED ANIMALS.

moner among the Bushwomen of South Africa than else-_

where.

But itis in the skull that the different races of mankind :

present the most striking osteological differences. The pro-
_yortions of the antero-posterior and the transverse dimensions

of the brain-case vary extremely. Taking the antero-posterior
diameter as 100, the transverse diameter varies from 98, or 99,
to 62. The number which thus expresses the proportion of
the transverse to the longitudinal diameter of the brain-case
is called the cephalic index. Those people who possess crania
with a cephalic index of 80 and above are called brachy-
cephali ; those with a lower index are dolichocephali. The
brain-case also varies greatly in its relative height. ‘The pro-
portion of the length of the cerebral chamber to the basicranial
axis (as 100) may rise to 270 in the higher, and sink to 280 in
the lower races; and there are great diversities in the extent
to which the cerebral cavity is rotated backward or forward
upon this axis. The position and the aspect of the occipi-
tal foramen vary considerably, as does the plane of that part
of the sguama occipitis which lies above the superior semicir-

cular ridge. The supra-ciliary ridges vary greatly in their”

development, and in the extension of the frontal sinuses into
them. They are nearly or quite solid in many Australian skulls.

In the size, form, and disposition of the facial bones, the
different races of mankind present great diversities. A line
drawn from the anterior extremity of the premaxilla to the
anterior extremity of the basicranial axis, may be taken to
represent the facial axis, and the angle included between
these two is the craniofacial angle. It varies with the extent
to which the face lies in front of, or below, the anterior end of
the cranium, from less than 90° to 120°. When it is great,
the face is prognathous,; when it is small, the face is orthog-
nathous. This is the fundamental condition of prognathism
or orthognathism. A secondary condition is the form of the
alveolar portion of the upper jaw, which, so far as it is ver-
tical, tends toward orthognathism; but, so far as it is oblique
and produced, tends to prognathism.

The arch formed by the teeth is,in the most orthogna-
thous races, wide and evenly rounded; while, in the most
prognathous, it is prolonged, and its sides are nearly parallel.
The teeth themselves are much larger, the roots of the pre-
molars and molars more distinct, and the hindermost molar
not so small relatively to the others, in some of the lower
races, notably the Australians.

THE ULOTRICHI AND THE LEIOTRICHI. 421

The mental prominence may project beyond the line of
the vertical alveolar margin of the mandible, in the higher
races, or it may be almost obsolete, and the alveolar margin
may be greatly inclined forward, in the lower.

The different races of mankind are divisible into two
primary divisions; the Ulotrichi, with crisp or woolly hair,
and the Letotrichi, with smooth hair. |

a. The color of the Ulotrichi varies from yellow-brown to
the darkest hue known among men. The hair and eyes are
normally dark, and, with only a few exceptions (among the
Andaman Islanders), they are dolichocephali. The Negroes
and Bushmen of ultra-Saharal Africa, and the Negritos of the
Malay peninsula and archipelago, and of the Papuan Islands,
are the members of this Vegroitd stock.

6. The Letotrichi are divisible into—

1. The Australioid group, with dark skin, hair, and eyes,
wavy black hair, and eminently long, prognathous skulls,
with well-developed brow-ridges, who are found in Australia
and in the Dekhan. The ancient Egyptians appear to me to
have been a modification of this race.

2. The Mongoloid group, with, for the most part, yellow-
ish-brown, or reddish-brown, skins and dark eyes, the hair
being long, black, and straight. Their skulls range between
the extremes of dolichocephaly and those of brachycephaly.
These are the Mongol, Tibetan, Chinese, Polynesian, Esqui-
maux, and American races.

3. The Xanthochroie group, with pale skins, blue eyes,
and abundant fair hair. Their skulls, like those of the Mongo-
loid group, range between the extremes of dolichocephaly and
brachycephaly. The Slavonians, Teutons, Scandinavians, and
the fair Celtic-speaking people are the chief representatives
of this division ; but they extend into North Africa and West-
ern Asia.

4, The dark whites, or Melanochroi; pale-complexioned
people, with dark hair and eyes, and generally long, but
sometimes broad skulls. These are the Iberians and “ black
Celts” of Western Europe, and the dark-complexioned
white people of the shores of the Mediterranean, Western
Asia, and Persia. Iam disposed to think that the Melano-

4292 THE ANATOMY OF VERTEBRATED ANIMALS.

chroi are not a distinct group, but result from the mixture of
Australioids and Xanthochroi.

Fossil remains of Men or implements of human manufac-
ture have hitherto been found only in late Tertiary (Quater-
nary) deposits, aud in caves, mingled with the remains of ani-
mals which lived during the glacial epoch.

INDEX.

A.

AccrPenseER, cartilaginous cranium of, 124,

Air-sacs in birds, 271.

Alimentary canal, 79.

Alligator terrapene, 171.

Amia, caudal extremity of, 20.

— calya, reproductive organs of, 126.

Amphibia, general characteristics, 149.

—— development, 164.

—— groups, 149,

— heart, 159.

—— limbs, 156,

— muscles, 45.

—— reproductive organs, 163.

—— respiratory organs, 161.

— teeth, 158.

Amphisbeenoida, 198.

Ankle-joint of sloths, 283.

Anoplotheride, 320.

Antibrachium, muscles of, 49,

Anthropide. See Man.

Anthropomorpha, general characteristics of,
402.

— comparison of, with man, 413.

— divisions, 403.

Aortic arches. See Arches, aortic.

Apes. See Simiade.

Arch, pectoral, 34,

— pelvic, 36.

— pectoral and pelvic, of chelonia, 178.

— pectoral and pelvic, of plesiosauria, 184,
185.

Arches, aortic, 83, 84.

—— number of, belonging to skull, 71.

— pectoral, and sternum, of a frog, 157.

Arches, visceral, skeletons of, TT.

Arctopithecini (marmosets), general charac-
teristics of, 392.

— brain, 394.

—— limbs, 393.

— muscles, 393.

—— skull, 393.

— teeth, 393.

—— vertebra, 393.

Armadillos, general characteristics of, 290.

Artiodactyla, non-ruminantia, 313,

—— ruminantia, 321.

Ascalabota, 194.

Australians, peculiarities of, 495.

Aves. See Birds.

Axolotl (Siredon), 161.

—— gortic arch of, S4.

BALZNOWRA, general characteristics of, 337
Baleen plates, or whalebone, 339.
Bats. See Cheiroptera.
Birds, general characteristics of, 168.
—— air-sacs of, 271.
brain of Meleagris gallopavo, 259.
— classification, 233.
— digits, 250, 254.
ear, 262.
— heart, 267.
—— larynx and syrinx, 267.
—— limbs, 249, 202.
—— lungs, 270.
—— muscular system, 257.
—— organs of copulation, 272.
—— pectcral arch, 247.
— pelvis, 251.
—— sacrum of a chick, 238.
— skull, 241.
—— spur, 254.
—— sternum, 240, 241.
—— vertebra, 236.
See also Fowl.
Bears, teeth of, 359.
Blood, circulation of, in frog, 160.
— corpuscles, 89.
Bloodsucking bats, 387.
Bones of cetacea, 335.
—— cynomorpha, 398.
— delphinoidea, 340.
— elephant, 360.
—— the face, 27.
—— fishes, 29, 79.
—— galeopithecus, 382.
—— hedgehog, 376.
— pig, 315.
—— rhinoceros, 308.
— the skull, 25, 26.
See also Os, Ossa.
Bosjesmen, fat of, 419.
Brain of anthropomorpha, 411.
carnivora, 351.
—— chimpanzee, 60-65,
—— cynomorpha, 402.
—— divisions.of, 55.
—- dog, 357
— frog, 162.
—— hedgehog, 879.
—— horizontal section, 56,
—— lemuride, 396.
—— longitudinal and vertical section, 57.

494 INDEX.

Brain of man, 417.
— marmoset, 394.

—— pike, 142.

— platyrrhini, 397.

— porpoises, 349.

—— rabbit, 60-65, 374.

Brain-case. See Skull.

Bruta, or Edentata. See Edentata.

Cc.

Ca sHALor, skull of, 341.

Cainozoic formation, crocodiles in, 221.

Camelide or tylopoda, 328

Canal, alimentary, 79.

— spinal, and cord, 64.

Canals of Stenson, 72.

Carnivora, general characteristics of, 350.

— classification, 358.

— divisions, 351.

Carpus, skeletal elements of, 31.

Catarrhine monkey, skeleton of, 392.

Catarrbini, characteristics of, 398.

Cats, teeth of, 359.

Caudal extremities of polypterus, amia, and
salmo, 20.

— vertebre, 21.

Cerebral nerves, 66.

Cetacea, general characteristics, 334.

—— grovps, 336.

Characters, distinctive, of vertebrata, 7.

Chalk, ichthyosauria in, 214.

— lizards found in, 196, 199.

Chameelonida, 198.

Cheiroptera, general characteristics of, 385.

— digits, 34.

—— position of limbs of bats, 33.

Chelone midas, carapace of, 173.

— section of skeleton of, 172.

Chelonia, general characteristics, 170.

— divisions, 179.

— heart, 264.

— lungs, 270.

—— muscular system, 257.

—— organs of copulation, 273.

—— pectoral and pelvic arches, 178.

—— plastron, 174.

— skull, 176-178.

Chelydra, fore-foot of, 33.

Chimera monstrosa, section of skull, 112, 113.

Chimpanzee, 404.

—-— brain of, 60-66.

Circulatory organs, 81.

Cochlea, development of, 75, 77.

Comparison of man with anthropomorpha,
413.

Corpuscles, blood, 89.

—— lymph, 91

Corpus callosum in mammalia, 59.

Cotylophora, 327.

Cranial nerves, 69.

—— system, 21.

Cranio-facial angle, 415, 420.

Crocodile, segment of endoskeleton in tho-
racic region of, 19.

Crocodilia, 214.

—— derma! armor, 214.

— ear, 262.

Crocodilia, groups, 221.

— heart, 266.

—— lungs, 270.
—— pelvis and hind-limb, 222,
—— reproductive organs, 272.

— skull, 218.
— teeth, 221.
—— vertebra, 215.

Crus, muscles of, 49.
Cutaneous muscle of hedgehog, 377.

—— porpoise, 345.

D.

Deer, horns of, 327.

Delphinoidea, characteristics of, 349.
Dental formule. See Teeth.
Dentition. See Teeth.
Development of amphibia, 163.

—— cochlea, 75-77.

egg, 9

DD) Ye
— fowl, stages of, 11, 18, 16, 23.
— lamb, 29.
— skull of fishes, 24.
— vascular system, 83-87.
— vertebrata, 9.

DIAGRAMS:
Accipenser, skull, 124.
Alligator terrapene, 171.
Amia, caudal extremity, 20.
Amia calya, reproductive organs, 126
Amphioxus lanceolatus, 104, 105.
Aortic arches, 83.
Axolotl, 161.
Bird and lizard, brain, 258, 259.
Cachalot, skull, 341.
Catarrhine monkey, 392.
Chelone, skeleton, shell, 172, 173.
Chelydra, foot, 33.
Chimera, skull, 113.
Chimpanzee, brain, 61, 63.
Crocodile, anterior thoracic region, 18
—— pelvis and hind-limb, 223,
— skull, 218,
Cyclodus (/acertilia), skull, 189, 190.
Dromeus, pelvis, and hind-limb, 228.
Dugong, heart, 332.
Elephant, skeleton, 364.
Fish, visceral arch, 77.
Foetus, human, principal vessels, 85.
Fowl, development, 11, 13, 16, 23.
fore-limb, 250.
— leg, 253, 254.
pelvis, 251.
sacrum of chick, 238.
scapula and coracoid, 247.
skull, 242.
spur, 254,
sternum, 241.
Flying fox, skeleton, 385.
Frog, nervous system, 65.
skull and brain, 152, 153, 162.
—— sternum and pectoral arch, 157.
Holoptychus, 127.
Homo, pregnant uterus, 9.
Horse, carpus, 299.
— cervical vertebra, 295.
— femur, 301.
— foot, 294, 298.
—— ossa innominata, 300.

ITT

INDEX.

Disgrams—continued.
Horse, aacyert 296.
—— tarsus, 293.
en ociras 208, 209.
Iguanodon, pelvis and hind-limb, 223.
Lamb, fcetal, head, 29.
Lamprey, skull and brain, 108, 110, 111.
Lepidosteus, 122.
Lion, skeletou, 352.
Lizards, pectoral arch and sternum, 35, 36.
— visceral arch, 77.
Mammal, visceral "arch, Ie
Monkfish (squatina), ‘pectoral member,

ao " skull, 115.

Mudfish, skull, 145, 146.

Orang, digit, 51.

Qs innominatum of man, 34,

Ostrich, skull, 243.

Ox, skeleton, 821.

Pig, brain, 61, 63.

Pike, brain, 142.

— outline, 41.

— pectoral arch and fore-limb, 137.
—— skull, 132-135.

Plaice, skull, 30.

Plesiosaurus, skeleton, 182.
Polypterus, caudal extremity, 20.
Pterodactylus, skeleton, 229.

Python, dorsal vertebree, 201.

—- skull, 203, 205.

Rabbit, brain, 61, 63.

Rattlesnake, skull, 206.

Oe en organs in higher yvertebra-

ta, 97.
Salamander, foot, 32.
Salmo, caudal extremity, 20.
Secretary- bird, skull, 245.
Shark, aortic bulb, 108.
Sheep, stomach, 328.
Skate, brain, 118.
Spatularia, skull, 128.
Sturgeon, skull, 124,
Tadpoles, 165.
Torpedo, 55.
Trematosaurus, skull, 155.
Turtle, heart, 265.
plastron, 175.
— skull, 175-177.
Vertebrate brain sections, 56, 57.
Whale, skull, 837, 338.
Dicynodontia, 222.
Didelphia, characteristics of, 276.
— | Sete ipa of, 277.
— stomach of, 280.
Digits of ane pomor pha, 406, 408.
— bat, 34, 385, 387.
— birds, 254,
—— cynomorpha, 401.
— dog, 354.
—- lacertilia, 196.
— lemuride, 389.
— man, 31, 413.
—— marsupialia, 279.
— muscles of, 50.
—— rabbit, S71.
-— seal and turtle, 34, 362.
Dinotherium, 366.
Dipnoi, 145.
Dog, anatomy of, 353.
— digits, 354.

425

Dolichosauria, 196.
Dromeus, pelvis and bind-limb, 228.
Dugong, heart of, 332.

E.
Ear, 74,
—— bones of whale, 338.
— in sauropsida, 262,
See Hearing, organs of.

Edentata entomophaga, groups and charac

teristics of, 287.
— extinct, 286.
— loricata, 289.
—— mutica, 287.
—— phytophaga, characteristics of, 282.
—— squamata, 288.
— teeth of, 282, 286.

Egg, development of, 9.
Elasmobranchii, 111.
Electrical organs, 54, 55.
Elephant, skeleton of, 564,
See Proboscidea.
Embryo of vertebrata, development of, 10.
Encephalon, 55.
Endoskeleton, segment of, in thoracic region
ofa crocodile, 19.
— of vertebrata, 14.
Entomophaga, 287.
Eocene strata, didelphide in, 280.
— extinct mammals of, 320.
—— fossils of equide in, 305, 306.
— fossil rodents of, 375.
Episkeletal muscles, 44.
Equide, fossil, 305.
—— (horses and asses) general charac‘eris-
tics of, 295.
See Horse.
Exoskeleton, 39.
— in birds, fishes, reptiles, and mammals,
40-43, 168, 235.
a reptilia, 167.
Eye-muscles of sauropsida, 259.
—— structure of, 72.

F.

Fog, bones of, 27.
— of man, 414, 420.
Facial muscles, 67.
Feathers, 235,
Femur of the horse, 301.
Fins of fishes, 39, 40.
Fishes, electrical organs of, 54.
eons in class, 103.
— limbs, 3
— muscular system, 45.
—— raylike bones, 29.
—— skeleton of visceral arches of osseous
fish, 78
— skull, 24, 80.
Fissipedia, general characteristics of, 351.
Flatfishes ( plewronectid@), 30.
Flying-fox, skeleton of, 385.
Feetal appendages of vertebrata, 12,
Foetus, human, arrangement of principa! ves
yi sels i Zs 85.
oot of anthropomor 407, 410.
— horse, 295, 298. phe
—— man, 415.

426

Fossils in chalk, 197, 198, 214.

— eocene strata, 280, 805, 306, 320, 375.

>— lias, 180, 214.

— human, 421.

— mesozoic formation, 185, 187, 195, 221,
227, 228, 280.

— miocene formation, 306, 807, 309, 312,
820, 828, 329.

— permian formation, 195.

—— post-triassic formation, 185.

— triassic formation, 195, 214, 221, 222, 281.

Fowl, stages of development of, 12, 17, 21, 28.

pelvis, 250.

seapula and coracoid, 247.

skull, 242.

sternum, 241.

tibia and fibula, 252, 253.

Frog, aortic arch of, 84.

brain, 162.

— cerebro-spinal and sympathetic nervous
system, 65.

—— circulation of blood, 160.

— larya, 165.

— skull, 152, 153.

—— sternum and pectorai arches, 156.

—

G.

GALEOPITHECUS, general characteristics of,
382.

Ganoidei, existing and fossil, 127.

— genera of, 121.

Gibbons, 403.

Glyptodon, peculiar character of, 291.

Gorilla, 404.

Growth in man, laws of, 418.

H.

Haas (marsipobranchit), optic nerves of, 65.
Hand of anthropomorpha, 403, 410.

Head and trunk, muscular system of, 44.
— of sperm-whale, 340.

Hearing, organs of, cases, 26.

— in cetacea, 349.

Heart of amphibia, 158.

— birds, 267.

crocodiles, 266.

— modifications of, 87.

— porpoise, 346.

— sauropsida, 264,

— teleostei, 140.

— turtle, 265.

Hedgehog, 375.

Ee papowanide, general characteristics of,

Homeeosauria, 195.

Horns of deer, ete., 827.

Horse, general characteristics of, 293.
—— cervical vertebra, 295.

— femur, 301.

-—— fore-foot and hind-foot, 294, 298.
-— limbs, 297.

-~— muscles, 301.

—— ossa innominata, 300.

—- skeleton, 296.

— skull, 297.

— teeth, 295, 302.

—— viscera, 304.

INDEX.

Hyposkeletal muscles, 44.
Hyracoidea, characteristics of, 867.

I.

IcutHyorsipA, characteristics of, 100.
Ichthyosauria, 208.

pectoral arch, 212.

—— pelvis, 214.

— skeleton, 209.

— skull, 210.

—— vertebra, 210.

Impregnation of vertebrata, 9.
Insectivora, characteristics of, 375.

J.
JACOBSON, organs of, 72.

K.
Kronoorantra, 196.

L.

LAcERTILIA, 186.
—— groups, 193.
organs of copulation, 272.
—— skull, 188.

Lamb, development of, 28.
Lamprey, optic nerves of, 66, 67.
—— sections of skull, 103, 111.
— skull, 24.

teeth, 79.

Larva of frog, 164.

Larynx, 93.

—— platyrrhini, 396.

—— sauropsida, 267.

Leiotrichi, 421.
*Lemuride, general characteristics of, 388
brain, 390.
—— limbs, 389.

organs of reproduction, 390.
— skull, 389

— teeth, 390, 391.

Lepidosiren, aortic arch of, 84.
Lepidosteus semiradiatus, brain of, 121.
Lias, chelonia in, 180.

—— ichthyosauria in, 214.

Limbs of amphibia, 156.

—— birds, 249.

—— carnivora, 351.

—— fishes, 87.

—— galeopithecus, 382.

—— hedgehog, 379.

— lemuride, 389.

—— man, 413.

—— marmoset, 393.

—— muscular system of, 46.
— pig, 315.

— porpoise, 365.

—— position of, 33.

—— seal, 361.

—— vertebrated animals, 31.
Lion, skeleton of, 352.

Liver, 79.

— in sauropsida, 264,
Lizard, brain of, 259, 260.
—— pectoral arch and sternum, 85, 26.

INDEX. 427

Lizard, skeleton of visceral arches, 77.
Lymphatic system, 90.
Lymph-corpuscles, 91.

M.

MAcRAUCHENID&, 312.

Mammalia, general characteristics of, 102.
— classification, 278.

— deciduate, 350.

—— dental formule, 81.

—— development of heart, 89.

—— skeleton of visceral arches of mammals,

TT.

— teeth, 303.

Man, arrangement of principal vessels in hu-
man foetus, 85.

— general characteristics of, 413.

ST eae ie ee of anthropomor pha with,

— digits of, 31.
— divisions of—
Leiotrichi, 421.
Ulotrichi, 421.

— fossil, 421.
— laws of growth in, 418.
— muscles of digits, 50-54.
— muscles of limbs, 46.
— 0s innominatum, 36.
— position of limbs, 33.
— “races” of, 418.
— section of pregnant uterus of a decidu-

ate placental mammal, 10.
— sexual differences, 418.
— teeth, 81.
Marmosets. See Arctopithecini.
Marsipobranchii, 108.
Marsupialia, digits of, 279.
Mastodon, 366.
Mesozoic formation, crocodiles in, 221.
— didelphidie, ete., tn, 280.
— lizards in, 194.
— ornithoscelida in, 227.
— plesiosauria confined to, 186.
—— pterosauria in, 228.
Miocene epoch, cotylophora of, 328,
-— extinct mammals, 320.
— fossil camelide, 329.
— fossil equide, 306, 307.
— fossil hippopotamide, 320.
— fossil rhinoceros, 310.
—— fossil tapirs, 312,
— genus of sirenia, 383.
Modifications of the brain, 59.
—— of the heart, 88.
— of Pe organs, 98.
Moles (¢a/pine), 38
Monkeys. See bimiade,
sn ola (squatina), pectoral member of,

a Pe uns of skull, 114.
Monodelphia, characteristics of, 281.
Mosasauria, 197,
Mudfish, 146.
Muscles of amphibia, 46.
— antibrachium, 48.
—— anthropomorpha, 408.
— crus, 48.
— qpoeeerohe, 400.
e digits, 50.

Muscles of dog, 355.

—— eye in sauropsida, 259.

—— fishes, 45,

— hedgehog, 377-879.

—— horse, 301.

—— the limbs, 47.

—— man, 416.

—— marmoset. 394.

—— ophidia, 256.

— pig, 515.

—— platyrrhini, 396.

— rabbit, 373.

—— seal, 362.

— system of, in ophidia, chelonia, and
aves, 256.

— trunk and head, 44.

Musk-deer, stomach of, 323.

Myelon, 65.

Myxine, 109.

N.

NEGROES, peculiarities of, 419.
Nerves, cerebral, 66.

—— of the eye, 73-75.

—— sauropsida, 258,

—— spinal, 65.

—— sympathetic, 71.
Nervous system of frog, 66.
Non-ruminating animals, 313.

Oo.

OLFACTORY apparatus, 72.

—— nerves, 66.

Ophidia, groups of, 200.

— fossil, 208

—. sees system, 256.

— organs of copulation, 272.

—— skull, 202.

— teeth, 208.

—— vertebre, 200.

Optic nerves, 66, 73, 74.

Orangs, 403.

—— middle digit of, 50.

Organs, circulatory, 81.

—— of hearing, 74.

—- renal, 94,

—— reproductive. See Reproductive Or
gans.

—respiratory, 91. See also Respiration.

— of sight, 72.

—— of taste, 78.

—— of touch, 78.

— of voice, 93.

Ornithodelphia, characteristics of, 27

Ornithoscelida, 228.

op een character of skeleton of,

Os innominatum of man, 36.

Ossa innominata of the horse, 300.
Ossification of facial apparatus, 27.
— skull, 24,

—— vertebre, 17.

Ostrich, reproductive organs of, 272,
skull, 243.

Otaridz (eared-seals), 360.

Ox, skeleton of, 321.

428 INDEX.

P.

PALZOTHERID &, 312.

Palate of cetacea, 336.

Pectoral arch, 34.

— in birds, 247.

— chelonia, 178.

— crocodiles, 219.

— and fore-limb of pike, 188.

—— of plesiosauria, 184.

Pectoral fins, 39.

—— member of monkfish (sqguatind), 38.
Pelvic arch, 36.

— of chelonia, 178.

—— of plesiosauria, 185.

Pelvis of anthropomorpha, 407.

—— bat, 386.

— birds, 251.

— cetacea, 335.

— crocodiles, 220.

— cynomorpha, 4090.

— hedgehog, 377.

man, 415; lower races of man, 419.
of platyrrhini, 395.

— porpoise, 345.

— pterosauria, 230.

—— sirenia, 331.

Permian formation, lizards of, 195.
Perissodactyla, 292.
Pharyngobranchii, 104.

Phocide, general characteristics of, 361.
Phocodontia, 349.

Phytophaga, 282.

Pig, anatomy of, 313.

— brain, 60, 65.

— digital muscles, 53.

Pike, brain of, 142.

— fins, 41.

— pectoral arch and fore-limb, 187.
— skull, 132-135.

Pinnipedia, characteristics of, 359.
—— groups, 360.

Pisces. See Fishes.

“ Placoid exoskeleton,” 111.

Plaice, skull of, 30.

Plastron of the chelonia, 174.
Platyrrhini, general characteristics of, 394.
Plesiosauria, 180, 185.

—— pelvic arch of, 185.

—— skeleton, 181.

os
—_—

— extinct, confined to Mesozoic rocks, 185.

Pleuronectide (flatfishes), 30.
Polypterus, caudal extremity of, 20.
Porpoise, general characteristics of, 342.
— heart, 346.

— muscles, 346.

— pelvis, 345.

—— respiratory apparatus, 347.

— skull, 343.

— stomach, 346.

—— teeth, 346.

—— vertebre, 343.

Post-Triassic group of plesiosauria, 185.
Poupart’s ligament, 37.

Primates, characteristics of, 388.

— divisions of, 389.

Proboscidea, general characteristics of, 364.
— bones, 366.

— fossil, 368.

— reproductive organs, 366.

— skuil, 364.

Proboscidea, stomach of, 556.
— teeth, 366

vertebra, 364.
Protorosauria, 195.
Protovertebre, 16.

Psalterium of ruminants, 321.
Pterodactylus, skeleton of, 229.
Pterosauria, 228.

— groups of, 231.

— skull, 229.

— vertebra, 229.

Python, dorsal vertebra of, 201.
— skull, 203, 200.

R.

Rassrt, anatomy of, 371.

brain, 60-65, 374.

—— digital muscles, 53.

— limbs, 373, 374.

—— muscles, 373.

—— reproductive organs, 374.

— skull, 372.

— teeth, 374.

—— vertebra, 371.

—— yiscera, 374.

Races of man, 418.

Rana esculenta, cerebro-spinal and sympa
thetic nervous system of, 65

Rattlesnake, skull of, 206.

Rays, pectoral arch of, 34.

skull, 24.

Renal organs, 94.

Reproductive organs, 95.

— of amia calva, 126.

—— amphibia, 165.

—— anthropomorpha, 413.

—— hat, 356.

—— birds, 272.

—— dog, 358.

—— hedgehog, 381.

-— lemuride, 390.

—— man, 415, 417.

—— modifications of, 97.

—— osirich, 272.

—— porpoise, 349.

—— sauropsida, 273.

Reptilia, characteristics of, 165.

groups, 169.

Respiration, mechanism of, 93.

—— organs of, 91.

— in amphibia, 161.

—— porpoises, 348.

—— sauropsida, 269.

—— teleostei, 140.

Rhinoceros, general characteristics of, 807.

—— bones, 308.

—— fossil, 309.

—— reproductive organs, 309.

— skin, 307.

— skull, 307,

—— teeth, 307, 309.

— vertebra, 307.

— viscera, 309.

Rhynchocephala, 194.

Rodentia, general characteristics of, 882,

brain, 370.

—- digits, 371.

—— reproductive organs, 371.

— teeth, 369, 370.

—— vertebra, 370.

— oe ee eS

INDEX.

Ruminating animals, 322.
— act of feeding, 234.
— act of rumination, 325.
— groups of, 326.

Ss.

SALAMANDRA, hind-foot of, 33.
Salmo, caudal extremity of, 20.
Sacrum of birds, 238.

Sauropsida, general characteristics of, 101.
— alimentary canal of, 262.

—— brain, 258, 259.

—— ear, 262.

— eye-muscles, 259.

—— heart, three forms of, 264
——--- larynx, 267.

—— liver, 264.

—— muscles and viscera, 256.
—— nerves, 253.

— reproductive organs, 272.
—— respiratory organs, 269.

—— stomach, 264.

— tongue of, 262.

Seals. See Otaride, Phocide, Pinnipedia.
Secretary-bird, skull of, 246.
Sensory organs, 72.

Sexual differences in man, 418.
Sharks, aortic arch of, 89.

—— aortic bulb, 116.

— pectoral arch, 34,

— skull, 24.

Sheep, stomach of, 323.

Shrews (sorices), 384.

Simiad, general characteristics of, 391.
—— divisions of, 392.

— skull, 391.

—— teeth, 391.

Sirenia, characteristics of, 539.
Skate, brain of, 118.

Skeleton, amphibian, 151, 152.

— of anthropomorpha, 404.

—— satarrhine monkey, 392.

— chelone midas, section of, 172.
— elephant, 364.

— flying-fox, 384.

— fossil equide, 305, 306.

— horse, 296.

—— icthyosauria, 209.

— limbs, 31.

— lion, 352.

a caine transitional character of,

—— ox, 321.
—— plesiosaurus, 182.
-—— porpoise, 343.
—— pterodactylus, 229.
—— the skull, 22.
—— visceral arches of lizard, mammal, and
fish, 78.
See also Endoskeleton, Exoskeleton.
Skull of accipenser, 124.
—— amphibian, 153.
— of anthropomorpha, 405.
—— arches belonging to, 71.
—— of bat, 386.
—— birds, 241.
—— carnivora, 350.
—— common fowl, 242.
—- cetacea, 334.

429

Skull of chelonia, 176, 177.
cranial system, 22.
crocodile, 218.
cynomorpha, 397.
dog, 353.

elephant, 365.

fishes, 31.

foetal cachalot, 341.
frog, 152, 153.
hedgehog, 376.
horse, 297.

lacertilia, 189, 190.
lemuride, 389.

man, 414, differences in, 420
marmoset, 393.
modifications of, 24,
mudfish, 145, 146.
nerves of, 66-71.
ophidia, 202.
ornithoscelida, 227.
ostrich, 243.

osseous brain-case, 24, 25

pig, 314.

pike, 132-135.

plaice, 30.

platyrrhini, 395.
plesiosauria, 183.
porpoise, 343.
pterosauria, 230.
rabbit, 372.

rattlesnake (crotalus), 206.
rhinoceros, 307.

seal, 362.
secretary-bird, 240.
sirenia, 330.

spatularia, 123.
sturgeon, 124.
trematosaurus, 123.
typical segment of, 25.
walrus, 360.

— whale, 327, 328.

Sloths, characteristics of, 28%
—— ankle-joint, 283.

—— limbs, 283.

—— pelvis, 283.

— tongue, 286.

—— vertebre, 283.

Snakes. See Ophidia.
Sorices (shrews), 384.
Spatularia, skull of, 123.
Spinal canal and cord, 65.
— system, 17.

Spleen, 91.

Spouting, mechanism of, in cetacea, 848.
Spur of birds, 254.

Squatina (monkfish), pectoral member of, 89
—— sections of skull, 115.
Stenson, canals of, 72.
Sternum in birds, 240, 241.
—— of frog, 157.

—— of lizard, 35, 36.
Stomach, 79.

— of camels, etc., 328.
— carnivora, 351.

—— musk-deer, 323.

—— porpoise, 346.

—— ruminating animals, 822, 328.
—— sauropsida, 264.

—— sheep, 323.

—— teleostei, 159,
Sturgeon, skull of, 24, 124.

WURUUDRPROUURRRRMOODURRROOURURRGGGDURD

£30

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— variations in, 318.
Sympathetic nerves, 71.
Syrinx, 93.

—— of birds, 268.

T.

TapPores, 165, 166.

Tapirs, characteristics of, 310.
Tarsus, skeletal elements of, 31.
Taste, organ of, 78.

Teetk, 79.

-—— of amphibia, 158.

=—— anthropomorpha, 411.
— bat, 386, 387.

carnivora, 300.

cats, 359.

cetacea, 335.

crocodiles, 221.
cynomorpha, 401.
delphinoidea, 340.
didelphia, 278.

dog, 356, 359.

edentata, 282, 286.
edentata tubulidentata, 288.
elephant, 365.

extinct mammals, 320.
fishes, 114, 138.
galeopithecus, 388.
hedgehog, 379.
hippopotamus, 319.
horse, 295, 302.

hyrax, 368.

lacertilia, 193.
lemuride, 390.
macrauchenide, 312.
man, 417, 420.
marmoset, 392.

ophidia, 208.
ornithoscelida, 227.
paleotheridex, 312.

pig, 316.

platyrrhini, 396.
porpoise, 346.

rabbit, 874.

rhinoceros, 307.
rodentia, 369.

seal, 363.

sirenia, 332.

suide, 313, 318.

tapirs, 310.

toxodontia, 329

walrus, 360.

whale, or whalebone, 339.
Teleostei, 130.

-——— aortic arch of, 84.
Tertiary epoch, extinct cetaceans of, 350.
late, fossil man in, 421.
Thymus, 91.

Tongue of amphibia, 158.
—-- sauropsida, 263.

— sloths, 287.

Torpedo, electrical apparatus of, 55.
Tortoises, 170.

Touch, organs of, 78.

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Toxodontia, extinct, characteristics of, 329.

Tragulide, 326.

Transition of skeleton of ornithoscelida, 224.

Trematosaurus, skull of, 155.

INDEX.

Triassic formation, crocodiles of, 221,
— extinct lizards, 195.

— dicynodontia, 224.

—— ichthyosauria, 213.

—— macropodide, etc., 280.
Triassic groups of plesiosauria, 185.
Trichechide (walruses), 360.
Trigeminal nerves, 68, 70.

Trunk and head, muscular system of, 4
Turkey, brain of, 259.

Turtles, 170.

— heart, 264, 265.

—— plastron, 174.

— skull, 176, 177.

Tylopoda or camelide, 328.

Ue
Utorricat, 421.
Ungulata, characteristics of, 292.

—— bat, 385.

birds, 236.

caudal, 19.

of carnivora, 350.
cetacea, 334.
crocodiles, 214.
cynomorpha, 398.
dog, 353.
hedgehog, 376,
horse, 295.

hyrax, 367.
‘chthyosauria, 208.
%certilia, 187.
zemuride, 389.
man, 414; lower races of, 420.
marmoset, 393.
ornithoscelida, 227,
ossification of, 17.
of pig, 313.
platyrrhine, 394.
porpoise, 343.
proboscidea, 364.
pterosauria, 229,
rabbit, 371.
rhinoceros, 807.
rodentia, 370.

seal, 360.

sirenia, 330.
snakes, 201.
tapirs, 301.

POE

—— development, 9.

-~— fcetal appendages, 12.
—— impregnation, 9.

—— limbs, 31.

—— provinces or groups, 100.
Vertebrate endoskeleton, 14.
— exoskeleton, 39.

Vesicles of the brain, 55.
Viscera of anthropomorpha, 412.
— camelide, 324.

—— cynomorpha, 401.

INDEX. 431

Viscera of elephant, 366. Visceral arches, skeletons of, 77.
—— hedgehog, 380. Voice of birds, 268,

— horse, 304. —— organs of, 93.

— hyrax, 368.

—— lemurida, 389.

_— pig, 818. Ww.
—— platyrrhini, 396, 397.

—— rabbit, 374. WHALEBONE, 339

— roedentia, 370. Whale, ear-bones of, 338.
— seal, 363. — skull of, 338.

—— tapirs, 311. — skull of fetal, 337.
Visceral arches and clefts, 14, —— sperm, head of, 340.

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