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CORNELL UNIVERSITY

THE
Flower Veterinary Library Be
FOUNDED BY 3
ROSWELL P. FLOWER

for the use of the

N. Y. STATE VETERINARY COLLEGE
1897

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DATE DUE

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This book was digitized by Microsoft Corporation in
cooperation with Cornell University Libraries, 2007.
You may use and print this copy in limited quantity
for your personal purposes, but may not distribute or
provide access fo it (or modified or partial versions of if)
for revenue-generating or other commercial purposes.

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MORPHOLOGY OF THE. verre .

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‘GEORGE DRYDEN.
. EDINBURGH : S44 LOTHIAN: STREET.
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CORNELL UNIVERSITY.

THE

Roswell P. Flower Library
THE GIFT OF
ROSWELL P. FLOWER
FOR THE USE OF
-THE N. Y. STATE VETERINARY COLLEGE.
1897

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MORPHOLOGY OF THE VERTEBRATA.

DOG-FISH, COD, PIGEON,

AND

Ee may

LIBRARY.

RABBIT.

BY

D. KNIGAT,

MUSEUM OF SCIENCE AND ART, EDINBURGH 3
FORMERLY MUSEUM ASSISTANT AT OWEN’S COLLEGE, MANCHESTER.

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GEORGE DRYDEN.: |

EDINBURGH: 54a LOTHIAN! STREET |
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PREFACE,

HE following pages are intended as a guide to those about to

commence the practical study of Zoology.

In selecting the Dog-Fish, Cod, Pigeon, and Rabbit, I have
done so, as they are easily procurable, and serve as good types of
their respective classes. . .

Each animal has, for simplicity, been described in detail :—
First,’ commencing with the external characters, then going on
to the alimentary tract and viscera, at the same time taking
up the generative organs. After that a description is given
of the respiratory and circulatory apparatus, following which
is a short account of the nervous system; and, finally, the
skeleton is treated of. .

Each animal is described from many careful dissections, and >
illustrations are given of those points which might appear
difficult. We should advise the student to provide himself. with
two specimens of each animal, one for the examination of the
“soft parts, and the other for the preparation of skeleton. For the
latter object it is best, after cutting off muscle, etc. to macerate
in water in some hot place for three weeks, not disturbing the |
jax or pot until the bones are taken out to be cleaned.

In conclusion, I have to state that certain facts in the course

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PREFACE,
of the descriptions are on the authority of the writings of
‘Gegenbauer, Parker, and Owen, notably the latter. ‘:

I must apologise to the reader for an accidental error in Plate I.,
containing skull of Dog-Fish: there are no teeth in the dry skull,
«as is represented.

At the end of the book is inserted notes on the Development
of the Dog-Fish, derived from the late Professor Balfour's work
on the “ Embryology of the Elasmobranchs.”

D. KNIGHT.

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CONTENTS, |

_

a eo PAGE
DOG-FISH, . oe ‘ : ‘ ’ a
©OD, . 16
‘PIGEON, . : . : : . 28
RABBIT, . i : ‘ 37
DEVELOPMENT OF THE DOG-FISH, : : OAL

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MORPHOLOGY OF THE VERTEBRATA.

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DOG-FISH.

Class—Pisces. Order—Elasmobranchii. Sub-order—Selachoidei.
Type—Scylium (Dog-Fish).

Note elongated pointed snout, and that mouth is on under
surface of the head, some distance from anterior extremity of
body. It is of great capacity, being the common entry to both
the digestive and respiratory organs; and as the transmission of
the food to the stomach, and of respiratory currents to the gills,
is performed by similar acts of deglutition, the bony arches which
encircle the mouth are large, and there is a complicated mechanism
for directing the nutriment and the oxygenating water each to
their respective destination. In front of the mouth are the two
nasal apertures, and on either side of it the external auditory
openings. Following at some distance from the mouth are five
vertical clefts on each side—these are the external openings of
the branchial sacs, which look backwards. Immediately behind
the last branchial cleft are the pectoral fins. In front of the
junction of middle third with posterior third of body are the
ventral fins, with the anus between their apposed bases. The
attenuated posterior end of body is continued into the heterocercal
tail, On upper surface of head behind each eye is an opening—the
~spiracle—which leads into the cavity of the mouth, and is the
remains of the first branchial cleft of the embryo. On dorsal
median line are two fins—the dorsal fins—one being anterior and
the other posterior. In some species of dog-fish a sharp thick
spine is inserted in front of the dorsal fins, which is known as
a dermal defence, this being of the same nature as the fossils
ichthyodorulites. The entire body is covered over by sharp,
closely set spines, arranged in regular oblique rows—the whole
constituting the shagreen. Each spine or denticle ‘agrees with a
tooth in structure, being developed in a papilla of the true skin,
or corium. A wavy line, the lateral line, runs on each side of the
body from behind the head to the tail. As the description of this

is more easily seen in_the cod, its structure will be described a
few pages on. Digitized b y Microsoft®

8 MORPHOLOGY OF THE VERTEBRATA,

ALIMENTARY TRACT.

‘Teeth are developed upon the mucous membrane covering the
_ palato-quadrate cartilage and the mandible: these are never
implanted in sockets.

The basis of the tongue is composed of the glossohyal bone, and
its surface is smooth and devoid of papille. There are no
salivary glands or tonsils, but mucous follicles pour their secretion
into the mouth. The entry to the gullet is simply constricted by
a sphincter muscle. .

The cesophagus is a short and wide canal, with a thick muscular
coat; its mucous membrane is longitudinally folded to allow of
increased capacity for unmasticated and often very large food.
It is not uncommon to find a large-sized fish in the stomach in
specimens after death. Numerous récurved processes project.
from the inner surface of the cesophagus. are

. The stomach is simple, and is a Jarge extensive sac, with a great
disproportion in size of cardiac and pylorice orifices. The inner
surface is rugose at the cardiac end: a circular pyloric valve is
well developed. The intestinal canal is shorter than the body
itself. The true homologue of the small intestine is extremely.
narrow and short. It loops upwards from lower end of stomach,
and receives the ducts of the liver and. pancreas. Beyond the
openings of these ducts it suddenly expands into the large =
intestine, which is straight and very short in proportion to the —
length of the body, and is continued to the anus, which opens.:
into the fore part of the cloaca. Ma

To recompense for the great shortness of the intestinal canal,
the absortive area of the mucous membrane of the large intestine is
increased by being raised into spiral transverse folds, forming the
so-called “spiral valve,” which runs throughout the entire length
of the large intestine in a cork-screw-like manner. This spiral
valve is both the homologue and analogue of the valvule con-
niventes of some mammals, man included.

The stomach and intestines are invested by the peritoneum,
and are connected with the dorsal wall of the abdominal cavity
by the mesogastric and mesenteric folds of the peritoneum.

The cavity of the peritoneum is in communication in front -
with that of 'the pericardium, to be presently alluded to, and
behind communicates with the exterior by two pores.

ae: 4

THE LIVER

Is of eS aa size, and is remarkable for the great ©
quantity of fine oil in its substance. It, is attached at the fore
part of the abdomen Biotieed, asda, partitioning off the”

ee

why

DOG-FISH. 9

_ pericardium, and extends backwards farther on the left than the
right side. ‘It consists of two lobes, which occupy a considerable ‘
portion of the abdominal cavity, and embrace the other viscera
below. The gall bladder, of small size, is situated towards the
fore part of the liver, and is attached to its right lobe.

PANCREAS

Is a spongy conglomerate gland, placed by the commencement of
the small intestine. Its duct terminates in a papilla, a short
distance from the pyloric valve.

KIDNEYS

Are two elongated convoluted bodies of a whitish colour, which
are situated on either side of the spine, extending as far forward
as the pectoral girdle.

The ureter, after quitting the hinder part of each kidney,
dilates into a kind of receptacle, behind each oviduct or vas
deferens, and communicating with its fellow near the cloaca,
terminates, by a single urethral canal, in the cloaca behind the
anus. The ureters should be inflated through this opening with
a, blow-pipe.

GENERATIVE ORGANS.

Male—The testes are very small, except in the breeding season,
and are situated far forward in the abdominal cavity. They have
a capsule—the tunica albuginea—which sends septa into the
substance of the gland, which consists of the tubuli testes,’
separated by a small amount of connective tissue. Numerous vasa
efferentia convey the semen to the beginning of the vas deferens,
which, by its many convolutions, forms a large epididymus.
‘These gradually decrease as the duct approaches the cloaca, when
it becomes straight, and expands into an elongated receptacle, the
surface of the mucous membrane of which is increased by many

-transverse folds. Posterior to the termination of the rectum, the
vasa deferentia suddenly decrease, and nearing one another,
communicate with the ureters.

Female—Ovary is single, and placed symmetrically in the fore
part of the abdominal cavity. It is round in shape, dense in
structure, and relatively small. The fallopian tube or oviduct
opens promixally into the cavity of peritoneum, between the liver
and peritoneal septum; while at its distal end it is dilated into
a uterine cavity,.which opens into the cloaca, being distinct

from the ureters. '
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10 MORPHOLOGY OF THE VERTEBRATA.

HEART

Isa muscular sac invested in pericardium, situated just in
front of pectoral arch, below the. hind part of the gills. It
consists of an. auricle, which receives venous blood from a sinus
venosus, and a ventricle, which is continued into an aortic bulb,
which, in virtue of its striped muscular fibres, is rhythmically
contractile. The interior of the bulb is provided with four
transverse rows of valves. Sinus venosus—a development of the
termination of the venous system, is situated just behind auricle,
and is only partly covered by the pericardium. The wall of the
auricle is thin, its only function being to impel blood into the
ventricle. The ventricular wall having a more powerful function to
perform, viz., to impel the blood throughout the entire body, is in
consequence proportionally thick. It is internally provided with
stout muscular bands—the musculi papillares—which project into
its cavity. There are two membraneous valves at the auriculo-
ventricular opening, which prevent, after the contraction of the
auricle, the reflux of blood into that chamber. .
The pericardium is perforated, communicating with the cavity _
of the peritoneum by the pericardio-peritoneal canal, which
bifurcates, after leaving the pericardium, into two canals, which,
after diverging from one another, open into the peritoneum
opposite the termination of cesophagus. The course of the
circulation is as follows :—The blood is collected by the great veins
-into the sinus venosus, which pours its contents into the auricle,
by the. contraction of which the ventricle becomes filled. The
ventricle, contracting in its turn, propels the blood through’ the
aortic bulb to the gills, where it is erated. From the gills it is.
carried by efferent branchial vessels, which by their confluence form .
the dorsal aorta—from where the blood is distributed to all parts of
the body. From this it is observed that the erated blood which
has passed through the gills is not returned to the heart, but is.
_ driven from the branchie into the aorta, from where it is conveyed
all over the body. The propulsive force necessary for this is.
derived from the heart itself, the valves in the aortic bulb giving ,
full effect to the contraction of the muscular wall of the bulb,

RESPIRATORY ORGANS

_Are in the form of five fixed flattened pouches. The branchial
chamber is divided by four partitions into five chambers, and the
branchial laminz are attached by the whole of one margin to each
septa. In this manner five pouches are formed, each of which opens
inwardly into the pharynx by a separate slit. The branchiak

clefts are not covered by any, opersuas membrane asin the cod. .

. into large ganglionic masses before they enter the olfactory ~~
_8acs.

core

DOG-FISH. ’ 18

NERVOUS. SYSTEM.

Fishes inhabit water in every part of the globe, and occupy it.
at different depths, and are required to subsist on various sorts
of nourishment; and ‘as they must therefore have different
capacities, they must have corresponding variations in the:
structure of their bodies. The appetite for food appears to be
their predominant desire, and providing for its gratification to-
form their chief occupation: and as this is very voracious, they

‘must be constituted not only with a peculiar digestive apparatus

but with subtlety for taking their prey, and strength for pursu-
ing it, as well as for defending themselves against the attacks of
their enemies, To the varying functions of the different organs.
the nervous system is appropriately adapted. When the sense of
smelling is most conducive to their convenience, as in the dog-
fish, there isa capacious nose, large olfactory nerves, and large-
anterior lobes of the brain ; and when seeing is more advantageous,
as in the cod, the anterior lobes are smaller, and the olfactory .
nerves decrease in the same ratio; the eyes are consequently

large, and the optic nerves and parts of the brain from which

they originate are proportionate with them. Besides the different.
form and size of the several portions of the brain generally
existing, it is furnished with additional lobes when extraordinary
powers are necessary. :

Brain consists of a large cerebellum covering the fourth ven-
tricle, the sides of which are folded, and known as the restiform.
bodies. In front of the cerebellum is the mesencephalon, and in:
front of this the thalamencephalon. The cerebral hemispheres
are united in the middle line; the olfactory lobes are continued.
from the anterior lateral portion of the cerebrum, and they dilate

The optic nerve is seen passing to the eye. The third nerve

is seen passing to all the muscles of the eye, except the superior °
oblique and external rectus. The fourth is seen passing to the
superior oblique muscle, and the sixth to the external rectus. |
The fifth is seen giving off three principal trunks beside the
auditory. The first passes in. two divisions through the orbit ;
these become united at the anterior part of this cavity, and the.
nerve is then continued forwards, giving branches to the cellular
structure in its course towards the end of the snout. The second
trunk passes on the fore part of the muscles of the jaw, gives a

large branch, which distributes filaments to these muscles and the.

upper and lower lips; it gives a large branch to the cellular
structure on the ventral surface of the snout, this also gives.

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12 MORPHOLOGY OF THE VERTEBRATA.

branches to the upper lip; it gives a large branch to the cellular
structure at the side of the head. The third trunk passes behind -
the muscles of the jaw, gives branches to these, and is distributed
on the skin about the mouth and gills; one of its branches forms
a ganglion, which gives off filaments to terminate about the
under lip. The auditory ‘portion of the fifth passes to the ear,
and gives branches to the sacs containing the cretaceous matter
and the globular enlargements of the semicircular canals, whilst
a nerve similar to the glosso-pharyngeal communicates with it
on the large sac, and gives filaments to the termination of a
semicircular canal, and then passes outwards to give filaments
on the surface of the first and the corresponding one of the
second division of the gills, and terminates on the membrane of
the mouth. The vagus is seen passing to the gills, giving fila-
ments to the muscular appendages of these, and then sending a
large branch to distribute filaments to every part of the opposite
surface of each division, except the first; it sends a branch
anteriorly to the stomach, which communicates with the
sympathetic; it sends a large branch posteriorly to pass under-
neath the muscles of the back, and give filaments to these in its
course; this branch lies upon and crosses the spinal nerves; near
‘the tail it emerges from underneath the muscles, and passes just
‘under the skin to the extremity of this part.
The optic nerves unite into a chiasma, but do not decussate.

ORGANS OF SENSE.

. EAR.

External aperture of, situated at margin of gape on under
surface of skull. e.

The labyrinth—the essential portion of the organ of hearing—
is entirely enclosed within cartilage. The semicircular canals are
arranged in the ordinary manner, being three in number.

= NASAL SACS.

Cavity of nasal chamber is double, each part opening by @
separate aperture on the under surface of skull at sides of mouth.
The interior of the olfactory chamber is lined by mucous mem-

brane, arranged in such a manner as to form numerous folds, by
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DOG-FISH, ° . 13

’ which its surface is increased in area, all of which are richly

supplied by branches of the olfactory nerves. Posteriorly the
nasal sacs are closed, there being no communication with the
pharynx, as there is in Mixine and Lepidosiren. Two processes.
project from the margin of each nasal opening towards one-
another, and divide the original simple aperture into an efferent
and afferent orifice. The olfactory sac is connected with the.
mouth by the nasal groove, which extends from the sac to the
pa of the gape. This represents the nasopalatine canal.
of man.

EYE.

Notice that anterior segment of the bulb is very much flattened. . '

The sclerotic coat is cartilaginous in texture. The ciliary pro-
cesses of choroid are rudimentary. ;

A highly vascular plexus—the choroid gland—lies on outer
side of choroid. The upper and lower lids are represented by
two small moveable pieces.

THE SPINAL COLUMN

Consists of the persistent notochord, with rudiments of the
superior and inferior cartilaginous arches which grow around it,
and so form cartilaginous circular centra. The entire verte-
bral column is divisible into not more than two distinct regions—
an abdominal and caudal region. The abdominal vertebre pos-_.
sess a superior or neural arch, through which the spinal cord:
passes, a superior spinous process—the neural spine, and a trans-
verse process on either side, to which the ribs are attached. There
are no marked transverse processes in the caudal vertebre, but
below the body of the vertebree are given off inferior or hemal
arches, which carry inferior spinous processes—the hzemal spines.
The extreme end of the spine is bent up so as to form an obtuse
angle with the trunk part of the spine, and the median fin-rays
which lie below it are much longer than those which lie above it,
causing the upper division of the caudal fin-rays to be much
smaller than the lower. This kind of tail is known ‘as hetero- .
cercal. $2
The first vertebra articulates with the skull by a single
median facet. . ; <
‘The ribs are rudimentary, and are buriedin the muscles, They

do not ‘enclose a thoracic cavity as in higher vertebrates,and there

is no sternum. Digitized by Microsoft®

14 ‘MORPHOLOGY OF THE VERTEBRATA.

SKULL

Is composed of cartilage without any trace of sutures, and devoid
of membrane bone; it articulates with vertebral column by a
median facet. The maxille and premaxille are absent. Teeth -
are developed in the mucous membrane, which covers palato-
‘quadrate and mandible. It is on account of this that these
cartilages are so well developed. The anterior end of right and
left palato quadrate are connected by ligaments. 5
7 be sympletie is represented by a process of the hyomandi-
ular.
- Cartilaginous filaments pass outwards from the branchial
and hyoidean arches, and support the walls of the branchial
Sacs.

Mandibular arch consists of two pieces, the upper one, the
palato quadrate, which is articulated to the base of the skull.

‘The most anterior part of skull—ethmoidial region—on the:
inferior surface of which is a nasal pit on each side. The cephalic
cartilage is prolonged forwards between the nasal pits into a
rostrum. The succeeding portion of the skull forms the orbits,
which is bridged over in front and behind by cartilage. Follow-
ing behind the orbital portion is the labyrinthic portion, which
encloses the labyrinth or essential organs of hearing. This is —
continuous behind with the occipital segment. In the middle.
line, between the labyrinthic segment and occipital, is a deep
depression, at bottom of which are two foramina.

BRANCHIAL SKELETON

Supports that part of the alimentary canal which subserves
respiration. It is made up of complicated cartilaginous rods,

which superiorly are connected with the spinal column by the
' pharyngo-branchial rods, and ventrally are united with one
another by single pieces—the copula.

The hyoid arch ‘has the same arrangement as the branchial
arches.

SHOULDER GIRDLE

Is seen in itssimplest form. It is composed of a piece of cartilage,
which forms an arch on either side, being united to its fellow
along the ventral median line, and placed just behind the last |
branchial cleft. The muscles which move the pectoral fins are
attached to it. It iymotaonnesietovithekull.

off®

Digitized by Micros

Digitized by Microsoft®

DOG-FISH. 15

PECTORAL FIN

Is composed of a stem which is made up of jointed pieces of
' eartilage, which articulate with the shoulder girdle by the inter-

mediation of three basal cartilages. The central stem is beset
‘on each side with lateral rays, which are jointed in a similar
‘manner as the stem. .

PELVIC GIRDLE
Is formed of two coalesced cartilages. The venteral fins have

the same characters as that of the thoracic, with the exception that
‘the rays are arranged in a less complicated manner.

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18 MORPHOLOGY OF THE VERTEBRATA.

bladder are derived from the vagus and sympathetic, and its
function is a mechanical one, regulating the specific gravity of the
cod, and aiding it to maintain a particular level in the water.

THE KIDNEYS

Form two elongated reddish-brown organs, which are situated
beneath the spinal column above the air-bladder, and extend the
whole length of the abdominal cavity, from the head in front to
the tail behind. They are divided, for descriptive purposes, into
three parts—the fore, hind, and middle kidney. They are broadest
and thickest anteriorly. The renal tissue is soft and spongy, and
is supplied by numerous small arteries from the abdominal aorta.
They receive a great part of their blood from the caudal vein,
which ramifies in them.

The ureter passes directly downward, and dilates inferiorly
into a bladder, which lies behind the rectum, and consists of two
portions, marked by a constriction. The bladder should be care-
fully blown out through the urethra. The urethra continued
from the bladder is a short tube, which opens behind the genital
apparatus,

GENERATIVE ORGANS.

Male—The testes are remarkable for their enormous increase
at the breeding season. When fully developed, they are commonly
known as the “soft roe.” The greater part of their substance is
composed of the tubuli seminiferi, which open at one end into
the wide commencement of the vas deferens, and terminate at
the other by blind extremities.

Female—The ovaries, popularly known as the “hard roe,” form
two lengthened sacs, with a thin fibrous investment and a peri-
toneal covering, being closed in front, but produced behind into
a short and wide oviduct, which coalesces with its fellow of the
opposite side into a single tube—the common terminal portion
being much dilated, and terminating behind the anus in front
of the urethra. The stroma, or that part of the ovary which is
the seat of development of the ova, is extended by being plaited
into numerous transverse folds.

CIRCULATORY SYSTEM.

The heart has the typical piscine structure. It consists of a
sinus venosus, pouring its blood into the single auricle, and a
single ventricle receiving blood from the auricle. The ventricle
is continued into the’ Gul eda Which it is separated by a

Digitized by Microsoft®

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single row of valves. The aortic bulb differs from that of the
dog-fish in not being rythmically contractile. The cardiac aorta
—the continuation upwards of the aortic bulb—divides into four
trunks the afferent branchial vessels, which carry the venous blood
to the gills; they course round the outer side of the branchial
arches, and supply each filament. The now arterialised blood is
collected into the efferent branchial vessels—one for each gill.
Each of these open into a trunk on either side—in fact, form it—
the right and left aortic arch. These two pass backwards, and
meet in the middle line beneath the vertebral column, and form
the dorsal aorta.

The most anterior efferent branchial vessel gives off a large
carotid branch, which runs forward under the base of the skull,
and this is joined with its fellow by a transverse branch, so that
an entire arterial circle—the circulus cephalicus—is formed beneath
the base of the skull. The most anterior efferent branchial vessel
also gives off the hyoidean artery, which courses along the
hyoidean arch, and usually terminates by a branch in the cephalic
circle, and by another enters a rete mirabilia, which is situated in
the inner side of the hyomandibular bone, and sometimes simu-
lates a gill in appearance, and hence known as the pseudo-
branchia. The branches given off from the rete mirabilia join
again into the opthalmic artery, which, piercing the sclerotic,
breaks up into a second rete mirabilia—the so-called choroid
gland, before its final distribution.

The efferent veins of the kidneys form on either side the
posterior venze cavee, which open separately into the sinus venosus.
Just before their entrance into the sinus venosus, the posterior
venee cave receive the anterior venz cavee, which return the blood
from the anterior part of the body.

RESPIRATORY ORGANS.

The branchiz are situated in two special chambers. placed
on each side of the neck. They are carried upon the outer
convex sides of the branchial arches, which are a series of bony
arches, five in number, connected below with the hyoid arch, and
above united with the base of the skull. The concave borders of
the branchial arches are beset with a series of processes, which
project inward toward the mouth, the function of which is to
prevent the passage of any particles to the branchiz which might
injure their delicate structure. The branchiz themselves have
the form of a double series of vascular plates or lamellae. These
lamelle are flat and pointed in shape, and are covered with a very
vascular mucous membrane, in which the capillaries of the

hial 1 ify.. Th ober of plat
branchial vessels rami Mtize 4 ¢ Diese t plates on one process has

22 MORPHOLOGY OF THE VERTEBRATA.

PECTORAL ARCH

Consists of the clavicles, long knife-like bones, pointed below,
where they meet each other in the middle line, and connected
together by ligament. Attached to their dorsal end is another
smaller bone, the supraclavicle, which articulates with another
bone forked in front—the post-temporal: one fork of which is
connected with the epiotic, and the other to the pterotic.

Attached to the back of the clavicle are two small bones, above
the scapula, and below coracoid ; articulating with these are five
basal cartilages, to which the fins are attached. The clavicle gives
attachment to a styliform bone, the post clavicular, which runs.
back among the lateral muscles.

SKULL.

As the arrangement of the various bones of the skull can be
readily seen by a glance at the accompanying plate, we only
a to draw attention to the most important points concerning
them.

The articular cup in the basioccipital for the atlas is a deep:
conical excavation.

The homologue of the suspensorium of the dog-fish ossifies so.
as to give rise to two bones: an upper broad hyomandibular,
with which the sperculum articulates; and a low style-shaped
bone—the sympletic— which is firmly held into a groove on the
posterior inner suface of the quadrate.

Meckel’s cartilage persists throughout life, but its proximal end
is ossified into the os articulare of the lower jaw.

On the under surface of the skull are two membrane bones—the
vomer in front, and the large parasphenoid behind, which covers.
in all the base of the cranium from the basioccipital to the vomer.

The ethmoidal cartilage remains unossified.

The opisthotic is a distinct bone, and the prootic well
developed, being placed in front of the anterior vertical semi-
circular canal, and behind the exit of the third nerve.

The maxille take but little share in the formation of the gape,
which is bounded by the backwardly extended premaxille above.

The palato-quadrate arch is represented by the palatine in front,
and the quadrate behind. In addition to these is an external
ectopterygoid, an internal entopterygoid, and a metapterygoid,

which envelopes the upper and posterior part of the primitive
quadrate cartilage.

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R

/

ay

8

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| Sympleetic

2 Ectoethmaida!
3 Stylohyal

4 Alisphenoid

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Post-t

emporat

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PIGEON. 23

PIGEON.

Class—Aves. Order—Carinate. Type—Columbus (Pigeon).

Body covered with feathers, which are a modification of the
epidermis. Take one of the larger feathers and examine for the
following parts :—

(1) A central axis—the scapus—forming the stem of the
feather, and divided into a lower hollow part—the calamus
or quill—where its base is implanted in a small sac of the
cutis vera.

(2) A rachis or shaft, which is four-sided, and is simply a con-
tinuation of the calamus; and

(3) The shaft which carries the lateral processes (barbs) of the
feather, collectively forming the vexillwm.

The calamus at its lower end has an aperture, through which
the pulp holding blood-vessels enter the ‘shaft. The barbs are
narrow processes, which at their free end taper to a point, and at
their bases are attached to the rachis. The margin of the barbs
are furnished with smaller processes, which form an open angle
with the barb, and hold the same relation to the barb as the barbs
do to the rachis. The extremities of the barbules are hooked, so
that the opposed margins of the barbs interlock together through
the medium of these barbules.

Each feather sac—into which the lower end of the calamus is
fitted—is provided with small muscles, which by their contrac-
tion can elevate the feathers. In the integument over the coccyx
is the wropygial or oil gland—this is a modification of a sebaceous
gland, and secretes an oily liquid, which the pigeon covers its
feathers with in the act of preening.

Note the position of the external nares, which are placed at the
sides of the upper mandible. They are wide and freely open, to
allow of easy ingress of air during respiration. The nasal
passages communicate with the palate and pharynx by two
distinct but contiguous apertures: a bristle should be passed
through the external nares to verify this. The external meatus
of the ear is seen behind and somewhat below the eye; and, by
careful inspection, a fold of the integument may be seen project-
ing from the fore part of the meatus.

Notice the third eyelid or nictitating membrane.

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24 MORPHOLOGY OF THE VERTEBRATA.

ALIMENTARY TRACT.

The tongue is hard,and, like the mandibles, is ensheathed in horn.
It essentially consists of a prolongation of the glossohyal bone, and
is chiefly adapted to fulfil the function of a prehensile organ, in
association with the beak. Salivary glands are developed on each
side of the interior of the mouth, and pour their secretion on
the food prior to deglutition. It is destitute of papilla, except at
its base: these papilla are supplied by filaments of the glosso-
pharnyngeal nerve. No branch of the fifth nerve goes to the
tongue.

The cesophagus is long, and as it passes down it inclines
towards the right side, being partially covered by the trachea,
and connected to the surrounding parts by a loose cellular tissue.
It is dilated into a pouch: the crop, which is double, consisting of
two lateral oval cavities, lodged between the coalesced clavicles.
The change the food undergoes in the crop is well known: if a
pigeon be allowed to swallow a great number of peas, they will
swell to such an amount as almost to suffocate it. Hunter made
many observations on the crop of pigeons, which takes on a
secreting function during the breeding season, for the purpose of
supplying young pigeons in the unfledged state with a suitable
diet for their tender condition. An abundant secretion of a milky
fluid is poured out into the crop, and mixed with the macerating
grains. This is a near approach to the mammary secretion of the
mammalia.

The cesophagus, a short distance below the crop, opens into the
proventriculus, which corresponds to the pyloric of the stomach
of higher animals—a gastric juice being secreted from glands in
its walls. At its lower end the proventriculus embouches into
the gizzard, a thick-walled muscular sac, situated below the liver
on the left side of the abdomen. Its upper end has two apertures:
one of these is of large size, communicating with the proven-
triculus; the second is close to and on the right side of the pre-
ceding, leading to the duodenum. Below these apertures, the
cavity of the gizzard extends to form a cul de sac. At the middle
of the anterior and posterior parts of the cul de sac there is a
tendinous centre, from which the muscular fibres radiate.

In opening the gizzard, notice that the epithelium is developed
into a hard horny coat, adapted for triturating the food.

The pyloric orifice of gizzard is guarded by a valve. The

‘intestines reach from the stomach to the cloaca: in relative length
they are short. The canal is divided into small and large
intestines, by the insertion of two short cceca, which are opposite
one another. In the crown pigeon these cceca are altogether

ing,
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PIGEON. 25

The large intestine is very short, about one-tenth part of the
length of the body, and is continued straight from the cceca to
the cloaca. The rectum terminates ‘by a valvular circular orifice
in the cloaca.

THE LIVER

Is a large two-lobed organ, which occupies the front part of the
abdominal cavity, monopolising a great portion of its space.

The right lobe covers the beginning of the duodenum, pancreas,
and part of the small intestines ; the left lobe covers the proven-
triculus and part of the gizzard; while the apex of the heart is
received between the upper end of these two lobes. Of the two
hepatic ducts, one, the right and larger, enters the beginning of
the duodenum, the other near its termination.

The portal veins are of great size.

SPLEEN

‘Of small size, of a reddish colour, and of oval form, is placed
beneath the liver, on the right side of the proventriculus. A
process of the pancreas passes into close contact with it.

PANCREAS

Is of large size, and consists of two distinct portions, but these are
so closely applied together that they appear like one continuous

land. It is of an elongated and narrow form, and is situated in
the fold of the duodenum, and is more or less bent upon itself.
It has three ducts, two of which open into the duodenum separately,
close to the larger hepatic duct, while the third duct terminates
at a distance from the other two. .

THE KIDNEYS

Are two elongated organs, placed on either side of the vertebral
column, commencing immediately below the lungs, and extending
along the spine as far as the termination of the rectum. They
are moulded to the cavities and depressions of the pelvis. The
posterior surface exhibits inequalities corresponding to the emin-
ences and depressions of the pelvis. Each is invested by a capsule,
and consists of three principal lobes.

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26 MORPHOLOGY OF THE VERTEBRATA.

URETERS,

The duct of the kidney, is continued along the anterior surface of.
the kidney, receiving branches of the urinary tubules as it passes
along. Below the kidney the ureters pass behind the rectum,
becoming blended with its coats: they ultimately terminate upon
valvular elevations in the cloaca.

The supra-renal capsules or adrenals are of.a bright yellow
colour, and are placed on the inner side of the superior extremities
of the kidneys. They are in contact with the testes in the male,
and the left one adheres to the ovary in the female. They have
been found to shew an enlargement corresponding to the increased
development of the sexual organs. Their function is unknown.

TESTES,

Two in number, of an oval form, are placed near the upper end of
the kidneys, the left being usually larger than the right. They
are enclosed within a strong tunica albuginea, and are fastened by
a fold of peritoneum to the spine. They acquire an immense size
at the breeding season. The vas deferens, the duct of the testes,
passes down by the side of the ureters, and opens on a papilla in
the cloaca anterior to the opening of the ureter. The base of each
papilla is surrounded by a plexus of arteries and veins, and
serves as an erectile organ during coitus.

OVARY,

Only one, on the left side. The fallopian is long and tortuous, and
the ovum or egg, as it passes along it, receives the albuminous
investment—the so-called white of egg, which would serve for the
nutrition of the embryo had impregnation taken place. At its
lower end the fallopian tube is dilated, and it is in this situation
that the egg receives the calcareous shell. Lastly, the fallopian
tube opens into the cloaca, where the egg is received.

RESPIRATORY ORGANS.

THE LUNGS

Are spongy in texture, and of a bright crimson colour. They are
situated in the thoracico-abdominal cavity, and are firmly attached
to the ribs and their interspaces on either side of the vertebral
column, each lung being, moulded to the superjacent vertebrae and
ribs. They communicate with the large air sacs which extend

into the abdomen.
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PIGEON. 27

THE DIAPHRAGM

Is incomplete, and is attached to the ribs outside the borders of
the lungs and from the spinal column, and ends by an aponuerotic
expansion upon the ventral surface of the lungs. The lungs are
two in number, and extend from the second dorsal vertebra to
the kidneys, and laterally to the junction of the sternal with the
vertebral ribs. The pleura is reflected only over the sternal
surface of the lungs.

Each bronchus, as it enters the lung, immediately loses its
cartilaginous rings, and, after traversing the lung, ends at its
posterior part by opening into one of the abdominal air sacs. Canals
are given off from the inner side of the bronchus, which pass to the
under surface of the lung, and there open into other air sacs. Of
these there are altogether nine—two abdominal, before mentioned,
two anteriorly and two posterior thoracic, one clavicular, and two
cervical. All these air sacs, except the anterior and posterior
thoracic, communicate with an extensive system of air passages,.
which ramify through most of the bones of the skeleton with the
exception of the bones of the skull, which receive their air from
the nasal chambers and tympana.

LARYNX.

In the pigeon, as in all birds, there are distinct thyroid, cricoid,
and argtenoid cartilages. The voice is not produced in the larynx,
however, but in the lower larynx or syrinx. This is situated at:
the lower end of the trachea, at its point of division into the two.
bronchi. The syrinx is a complicated apparatus of cartilages and
bones, regulated by appropriate muscles. It is developed at the
junction of the trachea and bronchi, and from both—hence it is
known as the broncho-tracheal form of syrinx.

CIRCULATORY SYSTEM.
HEART

Is cone-shaped, and consists of two auricles and two ventricles.
Its apex is placed between the two lobes of the liver. As the
lungs are situated dorsally, the whole anterior surface of the
ericardium is brought into view when the sternum is removed.
The pericardium surrounds the heart, and adheres by its external
surface to the neighbouring air cells. The heart is of large size,
and is continued for some distance between the lobes of the liver.

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28 MORPHOLOGY OF THE VERTEBRATA.

The right auricle is larger than the left. The inner surface of
the marie is marked by the columne carne and musculi pectinati.

The right ventricle is a narrow cavity of a triangular shape,
placed to the right and anterior side of the left ventricle, but not
extending to theapex. The right ventricle is characterised by the
smoothness and evenness of its inner surface ; the pulmonary artery
takes its origin from it, and is provided at its commencement with
three semilunar valves. It divides into two branches—one for
each lung. The left ventricle is a cone-shaped elongated cavity,
the walls of which are about three times as thick as those of the
right ventricle, and have strong fleshy columns developed on their
inner surface, which extend from base to apex.

The aorta springs from the left ventricle—its orifice being
guarded by three semilunar valves.

The openings of the auricles into the ventricles are guarded
by the auriculo-ventricular valves, which prevent the regurgita-
tion of the blood backwards from the ventricles into the auricles.

The aorta is peculiar in crossing over the right bronchus. It
immediately after its commencement gives origin to the two
innominate arteries, which send off the common trunk of the
carotid and vertebral arteries.

The basilar artery is formed by the internal carotids, and not
by the vertebrals. The arteries of the hind extremities do not
arise from a single branch or external iliac, but from two arteries
which come off successively from the aorta at a considerable
distance from each other, and leave the pelvis by two separate
apertures.

The inferior vena cava receives the hepatic veins before it opens
into the right auricle. There is no renal portal system.

BRAIN.

The cerebrum does not cover the cerebellum, and its chief
mass consists of the corpora striati. The lateral lobes of the
cerebellum and pons varolii are rudimentary. There are no con-
volutions on the cerebral hemispheres, and the corpus callosum is
not developed.

The optic thalami are of small size, and are not united by a soft
commissure: between them is the cavity of the third ventricle.

SKELETON

Exhibits a far higher type than that of fishes. ;

As the beak in birds is prehensile, the cervical vertebra are
numerous, and freely moveable. In Columbus they are !¥§eiye
in number.

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PIGEON, 29.

Atlas is an oval ring-like bone, and the transverse ligament,
which is sometimes ossified, divides its aperture into two
—the upper, or posterior one, enclosing the spinal cord—
and the lower, or anterior one, the odontoid process of the
axis, which in reality represents the body of the atlas, as its
development shews.

The anterior articular surfaces of the remaining cervical
vertebree are slightly concave from above downwards, and
convex from side to side; while the posterior articular surfaces
are saddle-shaped, convex from above downwards, and concave
from side to side. So in a horizontal section, the centra
would appear opisthoccelous, while in a vertical section—
proccelous.

This is a well marked character of all birds. The several
arches have prominent pre and post-hysapophyses.

DORSAL VERTEBRA

Are seven in number, the posterior five being anchylosed to one
another. They may be known by their possessing ribs, and being
shorter than most of the cervical, but with broader neural arches,
in consequence of the greater development of the tranverse
processes.

From some of the centra of these vertebree inferior processes,
hypapophyses, are prolonged downwards, to allow of greater space
for the origin of the muscles which depress the neck, viz.,
lougus colli, and recti antici muscles. The centra have cylindrical
articular faces, like those of the neck:

The spinous processes are well developed. It is a character of
the dorsal vertebree that they have a small process on the body
of the vertebra for the head of the rib, while from the upper
part of the neural arch springs a more lengthened tranverse process
for the tubercle of the rib. e

LUMBAR VERTEBRA.

All are anchylosed, with the sacral to form a bone, which is
ordinarily known as the sacrum, to the transverse processes of
which the iliac bones are attached.

The first has a broad transverse process, which represents the
tubercular transverse process of the last dorsal. In all the
succeeding lumbar vertebre this process is prolonged downwards,
and in the last, it springs from the centrum and neural arch of
the vertebra and constitutes a broad process, which abuts against.
the ilium.

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30 MORPHOLOGY OF THE VERTEBRATA.

SACRAL VERTEBRA

Are four in number, and are all anchylosed together. From their
several arches are prolonged horozontal tranverse processes, which
are flattened from above downwards, and unite with the ilia.
The inferior surfaces of their centra are deeply concave, forming
-deep fossz for the reception of the middle lobes of the kidneys.

CAUDAL VERTEBRA.

The anterior of these have lamellar transverse processes. The
three first possess ribs, which are anchylosed at their proximal
extremities with both the centra and neural arches of their
vertebree, while at their distal expanded ends they abut against
the ilium. The anchylosed caudal vertebre are distinguished by
the name urosacral. The succeeding caudal vertebrae are
numerous and free, except the most posterior, which are
anchylosed into a ploughshare-like bone—named the pygostyle—
which supports the so-called preening gland and the quill feathers
of the tail (restrices). It is set on the spine, at a nearly vertical
angle with the axis of the body.

The bodies of the cervical and of those dorsal vertebrae which
are moveable are connected to one another by means of fibro-
cartilaginous rings, which extend from the circumference of the
one to that of the other. Each ring is prolonged in between two
contiguous centra into a dise—the meniscus—which is free on both
its anterior and posterior surfaces. This meniscus is perforated
at its centre. In this manner the synovial space between any
two centra becomes separated into two narrow compartments,
communicating with one another by the perforation in the
meniscus. In the caudal region, however, the meniscus is united
with the faces of the centra of the vertebrae, and so resembles an
intervertebral cartilage—like that of man.

THE RIBS

Are flexible arches of bone, which wall in the thoracic cavity
below. They are seven in number on either side—each dorsal
vertebra having a rib attached to it. The third, fourth, fifth, and
sixth are connected above with the spine, and below with the
sternum, through the intervention of the sternal ribs. The first
two are free ribs—that is, they have no connection with the
sternum. The ribs are situated one behind the other, in such a
way that spaces are formed between them, which are named the
intercostal spaces. They increase in size from the first to the

sixth. ee :
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PIGEON. 31

COMMON CHARACTERS OF THE RIBS.

A middle rib should be taken in order to study the typical
character of the ribs. Each rib presents for examination two
extremities, a superior or vertebral, and an inferior or sternal, and
an intervening portion—the shaft. The superior or vertebral end
shews a head, neck, and tuberosity. The head articulates with
the process before described on the body of the dorsal vertebre.
The tubercle presents an oval surface, for anticulation with the
extremity of the transverse process. The neck is the portion
included between the head and the tubercle.

The shaft is thin and flat. About its middle, from the posterior
margin, a process is given off, which curves upwards and back-
wards, and overlaps the succeeding rib: this is the uncinate process.

The first and last have no uncinate process. Each rib
articulates inferiorly with a straight rod-like bone—the costal rib
—which is to be considered as an ossified costal cartilage. The
first two ribs have no sternal ribs, while the last sternal rib does
not articulate with the sternum directly, but is blended with the
preceding costal rib.

The thoracic cavity is completed below by the large expanded
sternum, which developes from five centres of ossification. This
bone is placed in the middle line, and extends over the abdominal
cavity reaching to the pelvis behind.

The upper surface of the body of sternum is deeply concave and
boat-shaped, while at its anterior margin is a convex tranverse
grove on either side, for the reception of the sternal articulation
of the ecoracoids: these grooves meet in the middle line. The
costal border is thickened, and divided by transverse articula ridges
for the sternal ribs into hollows, which shew pneumatic foramina.

On the inferior surface of the sternum is a largely developed
descending vertical process—the keel. This affords additional area
for the origin of the great pectoral muscles which move the wing.

This osseous creast is convex along its inferior margin, being
of greatest vertical diameter in front, gradually lessening to its

osterior border. Its most anterior extremity is concave.

Along the lateral margins of the body are two processes on
either side, placed behind the articulations for the sternal ribs—
these afford attachment for fascia, which strengthens the floor of
the abdominal cavity behind.

‘

SCAPULAR ARCH

Consists of the scapula, the clavicle, and the coracoid, on each side.

The scapula is a long, thin, recurved sabre-shaped bone, being

thickest at the front, where it approaches the shoulder joint, at
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32 MORPHOLOGY OF THE VERTEBRATA.

which point it forms externally the posterior portion of the
glenoid cavity. Internally it is produced to meet the clavicle,
while at the remainder of its anterior surface it affords strong
attachment to the coracoid. The scapula is placed longitudinally,
extending backwards from the shoulder, parallel to the vertebrak
column, to which, however, it presents a slight convexity. Its
posterior third is bent downwards at a slight angle. It extends.
over four ribs.

CORACOID

Is the strongest of the bones entering into the formation of the
scapular arch. Its inferior end is expanded transversely, and is
received into the corner groove at the anterior margin of the body
of the sternum, before described. Its direction is upward, out-
ward, and forward, to the shoulder joint, where it is firmly
articulated with the scapula and clavicle, forming with the former
the glenoid cavity for the head of the humerus; at the inner
side of the humeral end it affords an articular surface for the
clavicle.

THE CLAVICLES

Are very early anchylosed into a V-shaped single bone, known
as the furculum (merrythought). 4 :

The apex of the V is united with the keel of the sternum by a
band of fibrous tissue. The principal use of this furcular arch is.
to act in opposition to the forces which tend, during the down-
ward stroke of the wing, to press the coracoid inwards, and also
by an elastic reaction to restore them to their proper position.

FORE-LIMB OR WING

Consists of a humerus, radius and ulna, two carpel bones, meta-
carpel and phlanges.

THE HUMERUS

Lies parallel to the axis of the body when the fore-limb is in a
state of rest, while the fore-arm is in a condition midway between
pronation and sipination. The proximal end of the humerus
is transversely expanded, and at its extreme end presents a
convex articular surface, which fits into the glenoid cavity of the
shoulder joint; on either side of this end is a ridge, which gives
insertion to the pectoral muscles. Its distal end exhibits two
facets, the outer being for articulation with the ulna, and the

inner with the radius, __ :
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PIGEON. 33.

RADIUS AND ULNA.

The former bone is always the more slender of the two. The

" Upper-end of the radius shews a cup-shaped depression, for articu-
lation with the inner articular surface of the lower end of
humerus. This end has also a convex border next the ulna, for
articulation with that bone. The ulna isslightly curved, and the
proximal end is most expanded, having an articular excavation for
the outer convex surface in lower end of humerus. The distal
end of the ulna is slightly expanded into a trochlear joint, which
articulates with the two free carpel bones—one, the scapho-lunar,
wedged into the radial part; the other, cuneiform, into the ulnar -

_ part, leaving an intermediate space for the os magnum, which is

confluent with the middle metacarpel.

The two most external of the normal five metacarpels are not, .
represented, but the remaining three are anchylosed together .-
with the os magnum, into a single bone. This bone appears as if ©
it were composed of two metacarpels, united at their extremities,
but free in the middle. — *

The outer metacarpel, that which corresponds to the radius, is.
the longer portion, and is, as its development shews, composed of».
two; it carries the digit which has the greatest number of
phlanges. This digit answers to the index finger, and consists of
three phlanges; the digit attached to the ulnar metacarpel con-
sists of only a single short phalanx.

OS INNOMINATUM

Is composed of three bones—ilium, ischium, and pubis—all of

which are indistinguishably anchylosed. In the young pigeon,

these bones were distinct. It is remarkable for the great elonga-_
tion, both anteriorly.and posteriorly, of the iliac bones, which. °
unite with the entire length of the sides of the sacrum. There
is an articular surface on the ilium, upon which the great tro-
chanter of the femur plays, called the antitrochanter. The
ischium broadens posteriorly, extending back nearly parallel to
the hinder part of the ilium, being united with it by ossification
behind. The pubis, after entering into the formation of the
acetabulum, passes downwards and backwards as a slender
curved bone, nearly parallel with the ischium. It is united with
its fellow only by fibrous tissue, there being no symphysis pubis.

FEMUR

Is a short bone with a small head, which fits into’ the acetabular
cavity of the innominate bone. The head is sessible on the shaft-—
that is, it has no neck. 4

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34 MORPHOLOGY OF THE VERTEBRATA.

THE TIBIA

Is the chief:and longest bone of the hind limb. The shaft is
straight and expanded at both extremities, being most so at the
proximal end. On the outer side of the upper end is a surface
for union by ligament with the head of fibula. At the lower
third of the shaft, the styliform end of the fibula is anchylosed to
it. To its lower end the oscalcis and caleaneum—the two largest
bones of the tarsus—are firmly and indistinguishably united.

THE FIBULA

Is a short styliform bone, about two-thirds the length of the tibia,
free at its upper end, but ancylosed to the lower one-third of the
tibia. The upper end of the fibula articulates with the outer
condyle of the femur: this is an important character in all birds.

TARSUS,

The proximal portion of this, as before mentioned, is anchylosed
to the lower end of the tibia (viz., oscalcis and astragalus). '

The distal portion, viz., the scaphoid cuboid and three cunei-
form bones, are anchylosed to the second, third, and fourth meta-
tarsal bones, to form the most characteristic bone in the leg of the
pigeon, viz. the tarso-metatarsal bone. This bone presents a
proximal end, with two articular cavities for the lower end of the
tibia, and at its distant end is divided into three trochlear con-
-dyles for the second, third, and fourth phlanges. There is also
at the distal end a rough impression on the inner side for that of
the first metatarsal.

THE TARSO-METATARSAL

Is followed by the digits, which consist of three toes directed
forwards, and one backwards—the hallux, which consists of two
phlanges ; the index, or the most internal of the three anterior
toes, is composed of three phlanges ; the middle, of four; and the
outermost, of five.
» The fifth toe is not developed, as in all other birds.

The toes are mechanically flexed when the pigeon is roosting

by the action of a muscle, which runs from the: pelvis, and is

attached to the flexor tendons of the toés.
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PIGEON. . 35

SKULL.

_ The various bones that compose the skull are fused together
in the adult pigeon, the sutures all being obliterated.

At the back and under part isa round foramen—the foramen
magnum—which gives passage to the termination of the spinal
cord. At its posterior part is a single rounded condyle—the |
occipital condyle—by which the skull articulates with the atlas
of the spinal column.

; zee nasal apertures are situated far back, near the base of the
eal. :

THE ORBITAL CAVITIES

Are large, and. placed laterally, and encroach upon the anterior
wall of the cranium—the septum separating the two being very
thin and delicate, and more or less incomplete. The roof of the

orbit is formed from before backwards by the frontal, prefrontal, —
and lachrymal ; and the hind wall by the frontal, alisphenoid, and
. basisphenoid. The brain case is arched and spacious. The
beak is chiefly formed of the premaxille, which are triradiate
bones of large size, and which give off three processes: a frontal
process, which ascends to the frontal; one placed along the middle
of the palate—the palatine process—to the palatine bones; and.
an external maxillary process, which composes the greater part
of the side of the beak, and unites with the maxilla. The two
bones are very early anchylosed, and form a single coalesced hone,
which is sometimes known under the name of the intermaxillary.

THE MAXILLA

Is a slender bone, expanded in front into the notch between the
palatine and maxillary processes of the premaxilla, being united :
also to the nasal and vomer. Posteriorly it is bifurcated where
it joins the jugal and palatine.

THE PALATINES

Are long slender bones. Anteriorly they pass under the maxillo
palatines, and unite with the premaxille—they join behind with
the pterygoids. Posteriorly the palatines converge toward
the rostrum of the basisphenoid, and are united to it by an
articular surface, which permits of a sliding movement of the
palatines upon the basisphenoidal rostrum. The pterygoids are
straight and slender bones. Their anterior or inner ends con-
verge and meet, while their posterior or outer end presents

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36 MORPHOLOGY OF THE VERTEBRATA.

fossa, for the articular head on the inner side of the distal end
of the quadrate bone. The quadrate is the moveable bone by
which the lower jaw articulates with the skull. It is articulated
in front with the prootic, alisphenoid, and squamosal; while its
distal end articulates with the mandible below—the pterygoid on
the inner, and the quadrato-jugal on the outer side.

: THE QUADRATO-JUGAL

Is a long and very slender bone, situated below the orbit. Pos-
teriorly it presents an articular head, which is received into a
fossa on the outer distal end of the quadrate. In front, it is con-
nected with the maxilla. .

From this arrangement it follows that when the mandible is
depressed, the quadrate is thrown forward, which movement
causes the quadrato-jugal and maxilla to move upward and:
forward; at the same time the pterygoids and palatines glide
forward upon the basisphenoidal rostrum—thus it comes about
that the beak is elevated when the pigeon opens its mouth.

THE SQUAMOSAL

Is chiefly applied to the side of the skull, and is anchylosed to the
other bones.

‘

THE VOMERS

Are early united into a single bone. It is narrow and elongated,
and in front it is pointed. Behind it is connected with the
palatines. The posterior nares lie between the palatines and the
vomer.
The eustachian tubes run through the basisphenoid, and open
' ‘by a common aperture upon the middle of the under surface of
the skull.

: THE BEAK

Consists of an upper mandible, supported by the maxille and

remaxillz, and of a lower mandible formed by the lower jaw.
These bones are provided with a sheath of horny fibrous tissue
in place of teeth—this sheath being moulded to the shape of the
osseous mandibles. ;

THE SENSE OF TASTE

Is imperfectly developed in the pigeon, as in other birds which,
having no masticatory organs, swallow their food almost as soon

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RABBIT. 37

al

RABBIT.

Class—Mammalia. Order—Rodentia. Sub-order—Dupliciden-
tata. Z'ype—Lepus (Rabbit).

Body covered with hair, which extends over the under surface
of the feet and into the interior of the mouth, so that on the
inside of each cheek is a band of hair.

There are five digits to the manus (fore foot), the pollex being
small. The hind limb is longer than the fore limb, and has four
digits. The large eyes are furnished with a third or nictitatin
eyelid, which contains a triangular cartilage. The large lachrym
gland lies above and on the outer side of the eyeball. The upper
lip is cleft in the middle. .

The recurved penis of the male has a scrotal sac on each side.
The female has five pairs of teats, placed along the side of the
abdomen., Both the male and female have perineal glands, which
are sac-like involutions of the integument—the duct of a gland
situated at the sides of the penis or clitoris opens into them.

The stomach is simple, and the pancreas is diffused and very
large, being situated in a fold of the duodenum: its ducts are

‘two,—one, the larger, opens into the intestine about eighteen
inches from the pylorus, far removed from the biliary duct; while
the smaller one opens just. by. the bile duct.

The cecum is very large, and has attached to it a glandular
vermiform appendix at its free end.

The kidney has a single papilla, which projects into the pelvis
of the kidney. .

The female has two uteri, which are entirely separate, and both.
open into a common vagina.

The vagina and urinary bladder communicate with the
vestibule which opens to the exterior. The clitoris is formed by
the united corpora cavernosa, and is the representative of the
penis in the female, and, like the penis, is pierced by the urethra.

In the male rabbit the inguinal canal remains permanently.
open, and the vas deferens opens into the large uterus masculinus,
which is situated behind the neck of the bladder, and which
communicates with the posterior and inferior wall of the urethra,
just behind the openings of the prostatic ducts. There is a. bone.
in the penis, and vesicule seminales and prostatic glands. are
present. The testes remain in the abdomen, and come down into
the groin in the breeding season. "

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38 MORPHOLOGY OF THE VERTEBRATA.

The thoracic cavity is separated from the abdominal by a
well-developed diaphragm (compare this with pigeon.) The heart
is four-chambered, as in all other mammals, and there are two
anterior ven cave. The external jugular vein is very much
larger than the internal. :

‘Of the muscles, attention may be drawn to the plantaris. This
muscle is peculiar in being very large, and terminating in a
tendon almost as large as the tendo achillis, which runs over
the end of the os-calcis, being separated from the tendo achillis by
a synovial sac. In the sole of the foot it divides into four tendons,
which are perforated for the long flexor tendons of the digits.
We mention this muscle because it differs from that of all other -
mamrnals in the aspect we have alluded to.

BRAIN.

The cerebral hemispheres do not cover the cerebellum, and
the fissure of Sylvius is rudimentary. The olfactory nerves are
immense. The corpus callosum is relatively small, and its
anterior end is but slightly bent downwards. There is only one
corpus mammillare, and in the corpora guadrigemina the nates
are larger than the testes. The corpora trapezoidea are well

developed.
SKELETON.

Seven cervical and nineteen dorso lumber vertebra, twelve of
these being dorsal. s

The transverse processes of the atlas are much expanded, and
the axis has a prominent long antero-posterior neural spine ;
while all the remaining cervical vertebra have short spines.

The spinous and transverse processes of the dorsal vertebrae
are well developed, the latter and the most anterior transverse
processes being especially prominent. At the eighth a process, or
metapophysis, springing from the side of the body of the vertebrae
between the spinous and transverse processes, becomes developed ;
and in the following vertebree this increases in size, till in the
lumbar region it becomes the length of the spinous process. It
. is short in the last lumber and obsolete in the sacrum, but is
discernable through the anterior caudal vertebrve.

' The transverse processes of the lumber vertebree are exceed-
ingly long, and project downwards and forwards. The transverse
process’ of the first lumber is bifurcated at its extremity. On
the ventral sides of the centra of the three most anterior lumbar
vertebrae strong median processes are developed, which look
downwards and forwards—to these are attached the crura of the

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RABBIT, =. 39
There are four sacral vertebre, only the first uniting with. the ilia,
The tubercles of the second, third, fourth, fifth, sixth, seventh,.
and eighth ribs are produced into spinous processes, which afford.
attachment to the tendons of the longissimus dorsi muscle.
The sternum consists of five segments or sternubre, with a long
-xiphisternum. The long narrow manubrium is keeled inferiorly.

FORE LIMB.

The acromium of the long narrow scapula sends a process back-
wards over the infra-spinous fossa, which gives attachment to a.
_portion of the trapezius muscle. The clavicle is slender, buried
in the pectoral muscles, and is incomplete at both ends. In the:
humerus there is supra-condyloid foramen. The radius and ulna.
are entire and in close contact, and. by reason of their hinge-joint
with the humerus, the movements of the fore-arm are restricted to
that of pronation. There is a ninth bone in the carpus—the os-
intermedium. There are five digits, the innermost being very short.
They are all ungulate, and provided with claws.

HIND LIMB.

The ilia are long and subprismatic where they articulate with
the first sacral—the joint being limited to this vertebra. They
extend in advance of this on each side the last lumber, expanding ~
into a crest, which is rough and slightly turned outwards. The
pubic bones are long and slender, and meet in the middle line in
a long symphysis pubis, which is prolonged into a ridge inferiorly,
_The'femur has a small third trochanter near the base of the
great one. The tiba and fibula are anchylosed, and the patella
is ossified. There are only two cuneiform bones in the tarsus, the:
internal one being absent. The navicular has a large process.
There is no inner digit, and the inner side of the base of the
second metatarsal is extended backwards to articulate with the
navicular : this may represent an interna] cuneiform. —

SKULL.
» 2—2 0—0 3—3 3—3
Dental Formula { it fe PM ee OM aC = 28

There are no canines. The lower and anterior upper incisors
are very long.’ They are coated with enamel only in front, and.
they grow continuously from persistent pulps. By attrition they
acquire a chisel-shaped edge.

The second pair of incisors in the upper jaw are very small, and
are placed behind the first pair. The incisors above and below
are separated from the first premolars by a long diastema.

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40 MORPHOLOGY OF THE VERTEBRATA.

The molars and premolars all grow from persistent pulps, and
do not form fangs. Their crowns are transversely ridged. In the
young rabbit there are in the upper jaw three incisors and three
milk molars on each side. The lower jaw has only two milk
molars on either side.

THE PREMAXILLZ

Are extremely large, and bear the upper incisors. The orbits are
not separated by bone from the temporal fossee. The optic nerves
have a common outlet, the optic foramina being confluent, and in
this manner the orbits communicate with one another behind.
Each orbit presents a wide opening at its front part, which leads
into the lateral nasal eavity.

THE ZYGOMATIC ARCH

iv

Developes a small prominence, both from its hind and fore
extremities.

THE NASAL BONES

Are remarkable both in their length and breadth. They extend
further back than the long, slender nasal processes of the pre-
maxille. The tympanic is expanded below to form a bulla.

THE PALATE,
On account of the large size of the anterior palatine canals, is
‘reduced to a narrow bridge of bone, extending across in a line
with the premolar teeth.

Post-orbital processes project outwards and backwards from the
frontals. The glenoid cavity is elongated from before backwards.
The narrow olfactory fossa is continuous behind with the
cerebral fossa, which is separated from the cerebellar fossa, by
an upright tentorial ridge.

In the young rabbit an interparietal bone can be distinguished.

The lower jaw or mandible consists of two separated halves
or rami, united in front by a short symphysis. The angle of.
each ramus forms a broad compressed plate, with the lower border
rounded and thickened, so as to project beyond the posterior
border of the ascending plate. The ascending portion of: the
ramus is long, and the condyles are elongated from before back-
wards, so as to correspond with that of the direction of the
glenoid cavity. The coronoid process is well developed. :

HYOID BONE.

In this there are nodules, which represent the ceratohyals, the
epihyals, and thyrohyals, :
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DEVELOPMENT OF THE DOG-FISH.

THE OVUM

Is a minute oval body produced in the ovary—it consists of the
following parts :—

(1.) A yolk mass.

(2.) A small cell lying on the surface.

This cell is bounded by a dark outline, the vitelline membrane
and embedded in it is the germinal vesicle, inside of which again
isthe germinal spot. The germinal vesicle and spot represent,
respectively the nucleus and nucleolus.

The germinal vesicle and spot disappear before the ovum
leaves the ovary, this being independent of fertilization. Impreg-
nation consists in the entrance into the cell of a spermatozoon.
The spermatozoa are the male elements produced from the
testes. Each spermatozoon consists of a pointed head with a long
tail, and is actively motile, which property is due to the lashings of
the tail. After fertilization, the egg on its way down the oviduct:
receives a new investment of an albuminous material. After
impregnation, a furrow appears on the surface of the cell, which,
gradually deepening, at length cuts into two: while the same
process begins almost immediately in each half, and cuts it also
into two. The same process is repeated in each of the quarters,
and so on, until at last, by continued cleavings, the whole yolk
is converted into-a mulbery-like mass, the whole still enclosed
in the vitelline membrane. From this it is seen that only a. .
portion of the ovary undergoes segmentation, and is therefore
called meroblastic (i.¢., part only undergoing division).

The ova of all fishies, birds, and reptiles are meroblastic. On
the other hand, in the mammalia and amphibia the entire ovum
undergoes segmentation, and is hence termed holoblastic (ze.,

whole dividing). The ovum of Amphioxus is likewise holoblastic.

When. the peripheral cells, which are first formed, are fully
developed, they arrange themselves into a kind of membrane
at the surface of the yelk, at the same time assume a polyhedral

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42 DEVELOPMENT OF THE DOG-FISH.

Shape from mutual pressure, so as to resemble pavement
epithelium. The deeper cells of the interior pass gradually
to the surface and accumulate there, thus increasing the
thickness of the membrane already formed by the more superficial
layer of cells, while the central part of the yelk remains filled
only with a clear fluid. By this means the yelk is shortly con-
verted into a kind of secondary vesicle, the walls of which: are
composed externally of the original vitelline membrané, and
within by the newly formed cellular layer,—the blastodermic or
germinal memprane, as it is called. The blastoderm now splits
into two layers, called respectively epiblast and hypoblast. .A
number of cells now appear apparently from out of the substance
of the yelk lying beneath the hypoblast, and migrate in between
the epiblast and hypoblast, and so form a third layer or mesoblast
between the other two.

A groove then appears on the outer or upper surface of the
blastoderm, and named the medullary groove. —

The sides of this groove, which are called medullary folds,
rise upwards chiefly from a thickening of the mesoblast, and
tend to approach one another. This they ultimately do, first
anteriorly, and sometimes afterwards posteriorly. The groove is
thus converted into a canal—the spinal canal. A fold has mean-
while appeared anteriorly in direction at right angles to the
medullary folds. This fold marks the position of the future
head, and is hence called the head fold. It assisted in closing in
medullary groove in front, while somewhat later a similar fold
appeared posteriorly, helping to close in medullary groove behind,
called the tail fold. The mesoblastic cells that lie under the
floor of medullary groove separate from other mesoblastic cells,
and become elongated to form a rod-like structure—the notocord.
The hypoblast takes no part whatever in these changes, but lies
as a level layer underneath mesoblast.

It (ae., hypoblast), coincident with the appearance of head and
tail folds, &¢., becomes invaginated, and thus forms the primative

_ alimentary canal, closed in front and behind. Meanwhile, that por-

tion of the mesoblast lying on each side of notochord, beneath

medullary folds, split into two layers—one attaches itself to the
epiblast, forming with it the body-walls ; the other attaches itself
to the hypoblast, and assists it in forming the walls of alimentary

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DEVELOPMENT OF THE DOG-FISH. 43

canal. By separation of these two layers of mesoblast from one

another, a cavity is found, which afterwards becomes the general

body-cavity or pleuro-peritoneal cavity. This splitting of meso-
blast does not extend quite up to the walls of the medullary
canal, hence there is left along either side of the canal, between it
and the line along which the splitting begins, a tract or plate of
uncleft mesoblat, which receives the name of vertebral plate. The
moreexternal mesoblast, viz.that which snlitsis called lateral plate. ‘
In this vertebral tract the protovertebre appear. These are
merely the mesoblast cells of the vertebral plates cut up into
square masses. They do not correspond to the true vertebra, for:
not only are the true vertebrae. produced by them, but also some.

of the muscles and spinal nerves. It must be carefully noted, —

that in that part of the embryo which forms the head, the meso-
blast is never cut up into protovertebre, and never undergoes -
cleavage. The mouth first appears as a pit in the skin, which
deepens until it abuts against anterior end of alimentary canal.
Communication is made between the two by a solution of the
intervening walls. The cloaca is similarly formed. Meanwhile,
other parts of embryo are being developed, which may be
described systematically.

I.—DEVELOPMENT OF HEART AND BLOOD-VESSELS.

Heart is formed as an elongated tube (contractile) out of a
mass of mesoblast lying underneath the anterior part of the.
alimentary canal. To provide channels for the fiuid thus pressed
by the contraction of the heart, a system of tubes makes its.
appearance in the mesoblast throughout the embryo.

II.—DEVELOPMENT OF SPINAL CORD AND BRAIN.

We have seen how primitive cord was formed. It is at first a
canal, the cavity of which is of considerable width. By a multi-
plication of epiblastic cells which line it, the cavity is much
narrowed. ‘Thus the anterior and posterior columns and roots of
the spinal nerves are formed, as well as the commissures. The
cavity of the canal is now a mere slit, which is soon divided by a

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44 DEVELOPMENT OF THE DOG-FISH.

transverse partition into two—an anterior and posterior (lower
and upper respectively, if cord be supposed to be horizontal.)
By the absorption of the roof of the posterior slit, the posterior
fissure is formed. The anterior slit remains as permanent
central canal of spinal cord. The anterior fissure, which appears
before posterior, is formed by growing downwards of the parts of
the cord on each side of the middle line, so as to enclose a some-
what linear space.
Brain—Spinal canal dilates anteriorly into these vesicles—
anterior, posterior, and middle cerebral vesicles.
From the anterior are produced—
(1) Cerebral hemispheres.
_ (2) Corpora striati.
(8) Olfactory bulbs.
(4) Optic thalami.
(5) Pineal gland.
(6) Pituitary body or gland (in part).
(7) Third ventricle.
(8) Optic nerve (primary).
From middle cerebral vesicle—
(1) Optic lobes.
(2) Aqueduct of Sylvius.
(8) Optic nerve (secondarily).
From posterior—
(1) Cerebellum. .
(2) Medulla oblongata.
(3) Fourth ventricle.

DEVELOPMENT OF ENDOSKELETON.

(a) Vertebral Column—Protovertebre form true vertebrae, by
providing the notochord with a cartilaginous sheath, which
becomes constricted to form bodies of the vertebree, and sends
prolongations around spinal cord to form the neural canal.

(b) Skull—Two bars of cartilage appear at anterior part of
notochord—the parachordal cartilages. In front of these other
two—the trabecule cranii. These latter are at first separated
from one another and from the former, thus allowing a space to
intervene. Through this space the upper and back part of the

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DEVELOPMENT OF THE DOG-FISH. a AD .

mouth communicates with the brain. The trabecule then fuse '

with one another and with the parachordals, ‘and thus cut off the
upper part of the mouth, which is transformed into part of the
pituitary body. A cartilaginous floor is thus formed beneath brain
floor, grows outwards and upwards, fusing with the nasal and ear
capsules but not with eye capsules, and tries to roof in head, and
so form a complete cartilaginous box. It never, however, com-
pletely roofs it in, one or two spaces being covered by the skin.

VISCERAL ARCHES AND CLEFTS.

Below and on the sides of cranial parts of head,’a series of pro-
cesses or bars of cartilage are developed in pairs. The tissue

between these bars become absorbed, forming clefts, which remain

open for a longer or shorter period. The first cleft lies between
the first and second arch, so that there is one more arch than cleft.

There are seven branchial arches and six clefts. Cartilage
developed in first arch is called Meckel’s cartilage. From near
its proximal end another bar of cartilage is given off, which is
called the pterygo palatine. This forms the upper jaw, while
Meckel’s itself forms the lower jaw. Between the two the mouth
is formed. From proximal end of Meckel’s cartilage another
small cartilage is formed—the spiracular or meta-pterygoid—

which ossifies as the malleus in man. The second arch is called |

hyoid, and has three pieces—(1) Hyomandibular, which connects

jaws with ear capsule (connected to hyoid by a ligament). (2)

Basihyal, which goes to support tongue. (8) Hyoid piece itself.
Other five simply form branchial or gill arches.

The limbs are believed to be formed from arches called extra —

branchial arches. There are in addition five pairs of labial
cartilages :—First pair extending over nasal capsules ; second and

third pairs above nasal aperture; fourth pair in connection with ee:

upper jaw; fifth pair with lower jaw.

OLFACTORY ORGANS.

Two pits, one at each side, appear in primitive head. ‘These
deepen, and their lining cells become modified to receive sense

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46 .. DEVELOPMENT OF THE DOG-FISH.

impressions, and have branches of the olfactory nerve going ‘to
them. A capsule is formed round each for protection, which
fuses with the brain-box.

AUDITORY ORGANS.

On each side of posterior part of head a dimple appears, which
deepens into a sac, whose external opening becomes constricted.
The sac then gives off three projections in different directions; these
become compressed, and central portion absorbed, leaving three
canals, the semicircular canals, each of which of course com-
municates with the primary sac, which becomes the vestibule. A
cartilaginous capsule is formed around it for protection, which
fuses with the brain-box.

EYE.

Commences as a lateral outgrouth of anterior cerebral vesicle,
in form of a stalked vesicle. The stalk becomes narrower and
subsequently solid, and converted into optic nerve. This optic
nerve gets pushed backwards, so as to be connected with middle
cerebral vesicle, and some of the fibres get pushed over to opposite
side, forming the optic commissure.

The optic vesicle is pushed outwards until it comes in contact
with the skin (skin—superficial epiblast). The part of skin with
which it comes in contact thickens ; the thickened portion is then
pushed inwards in form of a shallow pit with thick walls, carrying
before it the front wall of the optic vesicle. To such an extent
does the involution of the skin take place, that’ the front wall of
the optic vesicle is pushed close up to the hind wall, and the
cavity of the vesicles becomes almost obliterated. The bulb of
the optic vesicle is thus converted into a cup with double walls,
containing in its cavity a portion of the involuted skin. We
may call this cup the optic cup. of its double walls—inner or
anterior is formed from the front portion, the outer or pos-
_terior form the hind portion of wall of the primary optic vesicle.
The inner or anterior, which very speedily becomes thicker than
the other, is converted into the retina; in the outer, or posterior,
which remains, thin pigment is eventually deposited, and it

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DEVELOPMENT OF THE DOG-FISH. 47

ultimately becomes the pigment layer of the choroid. By closure

of its mouth, the pit of involuted skin becomes a completely
closed sac. At the same time it becomes detached from: the

external skin, which forms a continuous layer in front of it—all
traces of original opening being lost. There is thus left lying i in

the optic cup an isolated mass of skin: this is rudiment of the

lens. The small cavity within it speedily becomes still smaller

by the thickening of its walls, until it disappears altogether. At

its first appearance, the lens is in immediate contact with anterior

wall of optic cup. In a short time, however, the lens is seen to

lie in the mouth of the cup, a space making its appearance

between the lens and anterior wall of optic cup. Walls on under |
surface of optic cup are at first imperfect, as a gap here exists.
Through this gap mesoblast, in which eye is embedded, passes out
and forms vitreous humour, the gap subsequently closing. The
mesoblast immediately surrounding the eye forms the choroid
itself (pigmented layer of which we have seen to be already
formed), and also the sclerotic. The front portion of walls of
optic cup, along with the choroid, bend in front of the lens, and
forms the iris. The original wide opening of optic cups is then
narrowed to a smaller orifice—the pupil—and lens which lay
before in the open mouth is now closed in the cavity of the cup.
Superficial skin becomes transparent cornea.

REPRODUCTION AND URINARY ORGANS.

In embryo there are many coiled tubes lying on each side in
abdominal cavity, and opening into it by both ends. These
being somewhat similar to the segmental organs of lumbricus:
may be called segmental tubes. A common segmental duct is
then formed on each side, which opens by one end into the
abdominal cavity, and by the other into the cloaca. Into this
common segmental duct each segmental tube comes to open by’
one end. The common segmental duct splits into two—the
wolfian and mullerian ducts. If embryo is to become a niale,
the former remains and the latter atrophies; and conversely, if
embryo is to become a female, the mullerian duct persists and
the wolffian duct atrophies. The segmental tubes may be divided
into an anterior, middle, and posterior set. In female, cells

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48 DEVELOPMENT OF THE DOG-FISH,..

lining abdominal wall on each side multiply and form the ovary.
Anterior set of segmental tubes disappear. Middle forms wolffian.
body, or parovarium, of unknown function. Posterior forms the
kidneys with their duct (ureter). Miillerian duct forms oviduct.
Kidney is thus formed of a number of tubes collected in groups,
forming the glomeruli of kidney. By blood-vessels being much
broken up in these glomeruli, the flow of blood is slow, and thus
‘watery contents are extracted. In male, anterior segmental tubes
form vasa efferentia and epididymis; middle set form wolffian
body. Posterior—the kidney. The lower portion of wolffian duct
remains as the vas deferens.

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