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LABORATORY MNNuAL OF
VERTEBRATE ZOOLOGY
LABORATORY MANUAL
OF
VERTEBRATE . ZOOLOGY
(For B. Sc. Students)
BY
S. N.
Lecturer
1n
PRASAD,
M. Sc., D.
PHIL.
Zoology, University of Allahabad.
AND
P. V. RAJAMANNAR, M. Sc.
Zoology Department, qniversi~y of Dellji.
With a foreword by
D. R. BHATTACHARYA, PH. D., D. Sc .• F. N. I.
Vice-Chancellor, University of Allahabad.
Formerly Professor of Zoology
ALLAHABAD.
UNIVERSAL BOOK COMPANY
20,
MAI{ATMA GANDHI MARG.
1951
Publislid by Sri Asanand for the rJ.lliversal
Book Co. Mahatma Gandhi Marg, Allahabad
Priltted by D. N. Bhargava at the l'zrthraj Press,
93, Chak, Allahalad
•
FOREWORD.
The method of teaching comparative
.ariatomy to students preparing for the
B~chelor's degree has much to recommend it.
'fhe student in the practical class, however,
&uffers from a great disadvantage.
The
theory work cannot be co-ordinated with the
-practical. For the Indian student the
.difficulty is more pronounced as there is no
practical manual describing all the Indian
types of animals for laboratory work.
In the present book the authors ha ve
tried to overcome this difficulty. They havenot only described all the Indian types, but.
_have covered the entire requirements of the
syllabus for the degree. Now that our
Universities are introducing Hindi as a
medium of instruction, the description of
.the Indian types will be very help~ul in
preparing text books in Hindi.
D. R.
Senate House,
University of Allahabad
August 1951.
BHATTACHARYA.
PREFACE
Practical courses in vertebrate anatomy vary in
scope and choice of material used.
There are
admirable books of proved merits, 'dealing with, the
laboratory requirements,; but they are not' satisfactory as
help books for an Iridian student. None J-nCQrpofates aU
the vertebrate typ'?s in one volume, ,and,. aborve all, none
describ61$ the Indian types tl}at are ,used' in our'laboraI'r·,
' " , ' ".
., ,r
tories.'
In preparing the· presel~t guide book 'two' things hit ve
a weighty influence-firstly, the requirement.~ of an Indian
student prep~rillg' for ,the,', degree' of Ba,chelor 'Of
Science, and 'secon(Uy 'the"lnccirporation of Indian types
used in our laboratories: ,The primary purpose of the·
present volume is to pr.Jvide.'a manual which o)1r students
may rise~ to advantage and' with· the help of'which they
may carryon work without supervision.' ,,'
<
All the dissections described in the book were carried
out in the laboratory p~rs9n~l\y by th~ a\lthors. Special
efforts were made to study ,and note down tne normal,
difficulties that the stu:le,nts aftf.n faoe, during the progress of their work, and attempts have been made to solve
them.
'
As most of the animals used in Otlr laboratories are
undescribed often interesting and new features have been
reported. For instance, one student pointed out; the prtlsence of a prominent branch of the carotid artery arising
just opposite to the origin of the vertebral artery in the
pigeon. This blood vess,cl is lllore prominent than the "ertebml and the oesophageal, arising from the same place,
natUIally the curiosity of a stude:lt could not be
PREFACE
viii
satisfied. The presence of the bloG<! vessel was checkf'd
in a large number of specimens during class work; and
quite a number were dissected by us. The same has been
nampd the cl)taneous. Lil<ewise the presence of an eitra
division of the coraco-brachialj~ brevis muscle in pigeons
~pecially kept for flight, a.nd the preSem(l of b )th the external jugular veins in the wall-li:~ard etr, have been noted.
It was pointed out to us by some of our senior colleagues that the nomenclature used while describing the
arteries of the head of tbe dog. fish is a bit confusing. We
agree with thtl above criticism, but, a.s we arc not in
position to check the same and changf'. we have used
the nomenclatur€'. as adopted by E. M. ThillaYl:lmpalam in hf:>r Memoir on ScollOdon, edited Itnd revised
by Professor .[{. N. Bahl, of Lucknow Unh-el ~ity.
a
It is a pleasure to ackno,vlil'dge the cordial cooperation
of a nnmber of senior members of the depltrtment in
discusaing the qis.sections and finally in t,he preliminary
preparation of the .manllscript. W £' art< indebted t.o Prof.
D. R. Bhattacharya, Ph. D, D. Sc. for writing the foreword.
'Department of Zoology
Uni'versity of Allahabarl
August, 1!J51.
S. N. Prasad.
CONTENTS.
Page
,.
vii
Preface.
Introdu ction.
Notes on Dissections-Notes on Drawing
CHAPTER
I
The Dog-fish.
External-'lharacters-The Coelom and viscera-Dissection of the Digestive system-Dissection of
Respiratory system-Dissection of Circulatory
system-Dissection of Renal and Reproductive
systems-Dissection of Sense organs-Dissection
of the Cranial nerves-The Skeletal system
CHAPTER
1
II
The Frog
Dissection of the Cranial nerve~-The Brain
CH.HTER
43
III
The Lizard (Varanus).
External features-Dissection of the Coelom
and viscera-Dissectiori of the Digestive system
-Dissection of the Respiratory organs-Dissection of the Oirculatory system-The Renal and
Reproductiv{' system-The SkeHal system
49
CONTENTS
:x
IV
CHAPTER
The Pigeon.
External characters-Dissection of the Muscles
of flight-Dissection of the Coelom-Dissection
of the Digestive organs--Disspction of the
Circulatory system-Renal and Reproductive
systems-DiE!section of the Brain-The Skeleton
of the fowl.
CHAPTER
Page
81
V
The Rat.
External features-Dissection of the Abdosystem--The
minal viscera-The Digestive
Thoracio viscera-Dissection of the Circulatory
system-Dissection of the Heart-The Urinogenital system-Dissection of the Neck--'I.'he
Brain-The Skeletal system
CHAPTER
121
VI
Histology.
Whole Mounts~Permanent preparations-Fixation-Staining etc.-Preparation of tissues.
CHAPTE:R
170
VII.
Histology tContd).
Examination of tissues-The Skin-Tooth
-Stomach-lntestine- LiverPancreasKS,.ney-Testis- Ovary.
184
CONTENTS
CHAPTER
Xl
VIII.
Page
The Development of the Chick.
t
The Egg-Fertilisation-Cleavage-Gastrutation Primitive streak-NotochordaL Process- .
Head fold-Coelom formation-Gut formationHeart forMation
,
(
195
CHAPTER
! .
IX.
Main Groups of Vertebrates.
-
Class Pisces-Class Amphibia-Class
Class Aves-Olass MarpmEJ.lia.
Reptilia~
209
Appendix.
Protochordata-Balanoglossus,' Ascid_ian ana
Amphioxus
"
240
LIST
OF ILLUSTRA.TIONS.
Page
(l) The Efferent blood vessels and the
arteries of the head of the. dog-fish ..
(2) The cranial nerves of the dog-fish
the
dog-fish and its visceral skeleton
15
29
(3) Lateral view of the skull of
35
(4) The fifth; sAventh. ninth and tenth
cranial nerves of the frog
44
anterior
view of atlas,
B, lateral view of axis, 0, lateral
view of .a typical cervical and
D, posterior view of a caudal
vertebra. of the va.ranUB
67
(6) Lateral view of the sacral vertebra
of the varanus
68
(7) The sternum of the varanus
69
(8) A, the dorsal view and B, the ventral view of the skull of the vara.nus ..
71
(5) A,
(9) One ramus of the lower jaw of the
75
varanus
(10) The circulatory system of the pigeon ..
93
(11) The circulatory system of the rat
132
(12) The male
the ra.t
142
urinogenital organs of
LIST OF ILLUSTRATIONS
Xl11
Page
(13) The urinogenital
organs of the
fem::lle rat.
144
(14) Diagram showing t,he arrangement
of bones of a mammalian skull
(15~
154
Sagittal section of t.he skull of the
dog
155
(161 The side vie"w of the skull of the
d~
(17) The egg of a hen
the shell removed.
l~
with half of
195
(18) Median section of c hick blastoderm
segmentation cavity.
197
(19) Vertical section of blastoderm show.
ing formation of the endoderm
198
(20) Surface view of the blastoderm
showing the primitive streak and
the formation of the notochordal
process
~21)
Transverse section of the embryo
showing the migration of mesoderm. .
(22) Surface view of 10·somite embryo
199
200
"
202
(23) Longitudinal section of a young
embryo showing the head fold
203
:24) Surface view of the embryo showing
head fold and formation of two
somites
204
LIST OE ILLUSTRATIONS
XIV
Page
(251 Transverse section of the lO·somite
embryo showing the forma.tion of
splanchnocoel.
205
(26) Transverse section through a seven·
somite embryo showing the formation
of foregut
206
(27) Transverse section of the embryo
showing the formation of the heart ..
207
INTRODUCTION.
Success in practical work depends upon siilCere
approach of the studoot. Presence of mind and common
sense add considerably to it. To perform any
practical well the student must, in some sense, get inside
its details and know what he has 'to do before starting.
A good student knows the tracks along which to proceed,
and he is constantly on the watch for the mistakes, which
he often tries to delude. The main spirit of his work is
to help himself to his best advantage and capacity. The
following pages contain all that is needed to guide such
a student-all the laboratory methods required by the
syllabus, along with notes on the important features of
the development of the chick and a brief summary of
animal classification.
Figures in such books do more harm than good because
of the student temptation to copy them. Therefore, only
a few illustrations have been given, where indispensable,
and those too are diagrammatic.
On Dissection,
Dissection means to cut open an animal to ascertain
tbe structure of its parts. For the purpose of the study
of gross anatomy it is necessary to spoarato the structures
from each other so 9S to give prominence to their outlines
and relationships. This is done by cutting away the
connectJive tissue binding the different parts. For a good
dissection a number of precautions are necessary.
(1) The most important of them all is the possession
of a good dissecting set. Some of our present day students
come without sets and att£lmpt to do their work by
borrowing instruments from their neighbours. This is a
uicidal habit which must be avoided at any cost.
INTRODUCTION
XVI
(2) So far as possible dissect the animals under water
in wax-trays. But large animals like the dog-fish and
the rabbit can be fixed to large wooden boards for dissectiqn. Keep the dissec~ion moist.
(3) Follow the instructions carefully, make a mental
picture of what you have to do before starting and proceed
with the dissection carefnlly and slowly. Do not wait
for the teachers to ~'p'ush" you through different stages, or
do not get impatient to see every thing Soon. Haste
alway!!. spoils ·dissections.
(4) Do not be afraid of breaking any thing
Breaking
is bad but not so bad that it may stop your progress
completely .
On Drawing.
Skt'tching is neither art nor scienc"'. it is l'll exercise in
(lommon-sense. It is something all students can- do well
if only they spend some time thinking how best to catch all
the characteristic point'> in one simple sketch. The mistake
with the majority is that the figures are drawn just to
satisfy them at the moment-later on the same fig'llre
may appear meaningless even to the authors. The important point is that a good sketch should explain its contents'
even to a layman. The object of the student should
be to devise figures which represent his main results at a
glance, yet so far as possible diagrammatic and semidiagrammatic figures should be avoided.
(1) The drawing should always he a faithful representation of the object or dissection, as such the object
must be before the student.
(2, The drawing should be large enougl• .to show all
the parts in actual proportion. Proportion is more importanl tha1J minute details.
XVll
I;\TRODUCTro~
t3) The lines must b~ clear and uniform. A broken
or confused line manifests confused bont of mind.
(4) Shading of any type shonId be avoidei so far as
possible. When extremely necessar.v pencils of different
hardness should be used but never different colours.
(5) The figures must be labelled just when drawn.
(6) The guide lines should not be scrawled across
hurriedly and without order. If so done they become
-either unduly obvious, or inconspicuous, and thus stand
out at the cost of the drawing. The guide lines should
be of uniform thickness with both ends without any
a.rrow my,rks.
'(7) The labelling should be done by "printing" the
names in block le~ters always, parallel to the base of the
page.
CHAPTER
I
THE DOG·FISH
The common dog·fish is a marine animal, ai such iu
the universities and colleges away from the sea-shore
only formalin preserved specimens are available for study
The characteristic feature of the dog.fish is that its entire
internal skeleton is cartilaginous, hence, included in the
class Chondroptery!!,ia. There are several varieties of
dog·fishes found off our coasts. The description below is
taken from one of the abundant species of the Indian
seas, the Scoliodon.
1.
EXTERNAL CHARACTERS.
(A) Shape of the body.
Long laterally compressed body, tapering at both
the ends, is the broadest in the region of the petoral
fins. The dorso-ventrally compressed head produced
into a flat pointed snout anteriorly. The head bears
two large circular eyes at its sides. The eyelids are
immovable and can 'hardly be distinguished from the
surrounding integument, but each eye is provided with a.
special eyelid, the nictitating membrane, which lies along
the antero. ventral border and can be drawn over the
eye in time of danger. The pupil is narrow and v~rtical.
The trunk passes on into tail compressed from side to side
and stlightly bent upwards. At the junction of the trpnk
and tail there are two shallow pits-one dorsally and
the other ventrally. These are the caudal pits. 'l'he
colour of the preserved specimen is dark grey dorsally,
whereas, the ventral surface is whitish.
1
THE DOG-FISH
A mere touch reveals that the entire body is covered
with small scales. On either side of the body there is a
faint line, the lateral line. extending from the head
toG th:2 posterior end of the hody.
(B)
The Fins.
The fins are flattened expansions of the skin, usually
triangular in shape, and supported by cartilaginous rods
and horny fin-rays.
(1).
Median Fins.
(i) The first dorsal fin is laqer, triangular in
shape situated a little infront of middle
of the body.
{ii) The second dorsal fin is
situated a little
distance behind the first and is similar in
shape though smaller in size.
{iii) The caudal fin forms a vertical fringe
round the posterior portion of the tail. It
is divided into twO\ lobes-dorsal and
ventral. The dorsal lobe forms a low ridge
along the grea tel' part of the upper surface
of the tail in the median line. The ventral
lobe is ·well developed divided into two
parts, a la.rger anterior and the other
posterior which is smaller.
{iv) The ventral median fin (anal fin) is
situated in the mid-ventral line slightly
infront of the caudal fin. This is almost
opposite the second dorsal fin.
THE DOG-FISH
(2). Paired fins (comparable with the limbs of higher
'Vertebrates.)
(i) The pectoral fins
are the largest among
fins, originating from the ventro-Iateral
margins of the body immediately behind
the gill-clefts. Note their triangular shape
and the space covered by them.
(ii) The
pelvic fins are smaller in size and
similar in shape; they arise close together
from the ventral surface of the body a little
infront of the middle of its length. Their
inner borders touch each other, and in the
male are fused together behind. They
enclose the cloacal chamber. In the
male a part of the fin on each side forms
a copulatory organ, the clasper. Each
clasper is a stiff rod-like appendage grooved
dorsally. The groove leads into a cavity,
; the siphon, beginning at the base of the
clasper.
(0) External apertures.
(1).
Median Apertures.
(i) The mouth
situated on
is bound by
bearing one
is a wide crescentic opening
the ventral side of snout. It
the upper and lower jaws each
or two rows of oblique teeth.
{Ii) The- cloacal aperture is an elongated
opening on the ventral surface of the body
between the pelvic fins.
4-
THE DOQ-FISH
(2). The paired apertttr.es.
(i) The nostrils are a pair of obliquely placed
crescentic apertures on the under surfaee'
of the head in front of the mouth. A small
fold of skin from the anterior edge covers
each nostril partially. The nostrils are
only olfactory Eitructures and not respiratory, as such, they do not open internally
into the mouth cavity.
(ii) The gill-clefts are a series of five vertical
"lits on each side infront of and slightly
above the pectoral fins. Pass a seeker
through the gill. clefts into the mouth and
note that they open obliquely backwards
into the giU.pouches and pharynx.
(iii) 'l'he
abdominal pores are a pair of
openings situated on elevated ptotpillae, the
cloacal papillae, on either side of the
cloaca. Through these minute pores the
coelom communicates with the exterior.
(3). Scattered apert1tres.
,
Examine the head carefully and note numerous groups.
of small openings on the, head and snou~. These are
the apertures of the ampullary canals. To make these
openings more obvious squeeze the head and note minutedroplets pouring out of the openings.
D.
THE EXOSKELETON.
The skin is covered with minute dermal denticles orplacoid scales which are arranged in regular oblique
rows and form the exoskeleton of the shark. These sca.les.
are derived from the skin.
THE DOG-FISH
5
Cttt a small piece oj skin and boil it Jor a few minutes
in 20% solution of caustic potash. Allow it to stand. If
the scales have isolated they will settle down at the bottom of
the tube. Decant the fluid, add sonte water and again
decant. After washing in water, thus, mount the scales in
glycerine and examine.
Each scale consists of a diamond-shaped basal-plate
from \vhich a flat trident spine projects out. The spines
are directed backwards2.
THE COELOM AND VISCERA.
Lay the animal on its back on the dissecting board and
pin dow1~ throngh the fins. Determine the positions of the
pectoral and pelvzc girdles by feeli1tg them through the skin,
the pectoral girdle being a little infroni of the pectoral fins,
and the pelvic girdle a short distance in/ront of the cloacal
aperture. Now give a mid-ventral inctszon extending from
the pelvic girdle to the pectoral girdle. Cttt through the
body-wall tl'ansversely just behind the pectoral girdle and
pin the two fiaps down.
A~
The Coelom.
'fhe spacious coelom is divided into two unequal
cavities, the pericardial and the abdominal, separated
from each other by a membranolls partition, the septum
trallsversum. The pericardial cavity is a small triangular.
space lying beneath the pharynx and surrounding the
heart. Thp abdominal cavity is quite large surrounding the
viscera. and communicating with the exterior through
the abdominal pore.
B.
The Viscera.
I dentijy the positions and relations of the fullowing
organs before proceeding further with the dissection.
6
THE DOG-FISH
(1). The heart is almost triangular in shape lying ill'
the pericardial cavity.
(2). The liver is a large solid elongated gland. It haa
two lobes uniting anteriorly. A median suspensory
ligament connects the liver lobes with the anterior waH
of the abdominal cavity. Embedded in the right lobe is
found a V.shaped thin-walled sac, the gall bladder.
(3). The stomach, a wide muscular tube, occupies the
major portion of the body cavity lying between the liver
lobes.
(4). The spleen is a large brownish-red body attached
to the loop of the stomach.
(5). 'The pancreas is a whitish, laterally compressed
body lying in the loop ~f the stomach and t'"e intestine.
(6). The intestine is a nearly straight tube running
upto thQ cloaca.
('7).
The Gonads.
(i) Female : The ovary is a median organ lying
on the ventral side of thE' vertebral column
just behind thG base of the liver. The tubular
oviducts extend through the entire length of
the body cavity uniting behind to form the
vagina which opens into the cloaca. Between
the ovary infront, and the coecal gland
behind extends a long tubular strand of tissue,
the epigonal oI'gan.
(ii) Male: The testes are a pair of elongate
structures, whitish in colour, lying along the
dorsal region of anterior two-third of the
abdominal cavity.
THE DOG-FISH
7
(8). The kidneys are a pair of long ribbon-like
glandular structures lying dorsally to the peritoneum. and
extending from the root of the liver to the cloaca.
(9). The peritoneum is the smooth membrane lining
the body cavity. In the mid·dorsal line it is reflected
beneath the vertebral column to form a double fold of
membrane, the mesentery, which suspends the gut.
3. DISSECTION OF THE DIGESTIVE SYSTEM
A.
Alimentary Canal.
(I). The mouth, ventral and crescentic, opens into
dorso-ventrally compressed spacious buccal cavity which
is lined with thick mucous membrane. The mucous
membrane is raised ventrally into a thick fold forming
thc non·muscular and non.glandular "tongue".
(2~. The teeth are oblique and have sharp, more or
less, compressed cusps, the edges of which are smooth and
non-serrated. The teeth are all similar in shape, homodont,
and are borne in several parallel rows on the inner
margins of the upper and lower jaws.
(3). The pharynx: The buccal cavity opens into the
pharynx on either side of which lie the internal openings
of the spiracle and the gill-pouches.
The spiracle is vestigial (not visible externally in
S::diod:m) rcpresfmted hy an inconspicuous oval pit.
The gill-pouches are .arge. Internally the pharynx is
lined with mucous membrane containing numerous
dermal denticles.
Note: The study of the buccal cavity and the pharynx
should be attempted after completmg the dissection of
blood vessels.
8
THE DOG-FISH
(4). The oesophagus: The pharynx narrows posteriorly to form a short oesophagus, the inner lining of which
is thrown ipto longitudinal folds.
Cttt open the oesophagus to see the folds.
(5). The, stomach is a. horse-shoe-shaped tube, the long
proximal limb of which is called the cardiac stomach,
whereas, the short distal limb is thE' pyloric stomach. At
the junction of the two limbs is a blind outgrowth, the
"blind sac". The inner mucous lining of the stomach is
also thrown into longitudinal folds that end in the depression of the "blind sac". 'fhe lining of pylorus is quite
smooth proximally but slightly folded distally.
Give a median longitudinal incision to the stomach and
exami1te it~ internal make·1~p.
(6). The bursa entiana is a thick. walled muscular
chamber into which the pylorus opens anteriorly. The
opening of the pylorus i8 guarded by a. pyloric valve.
The bursa entiana continues into t,he intestine.
(7). The intestine is a wide tube running straight
backwards into the' abdoniinal cavity and opens posteriorly into the rectum.
Cut open the intestine by a longitudinal incision along
iis right side and along its whole length. . Wash Ollt its
contents and examine.
The internal surface of the intestine is increar:Jed by a
characteristic fold of mucous membrane, the scroll
valve, having one edge attached to the inner wall of the
intestine and the other rolled up longitudinally on itself
into a scroll, making an anti-clock-wise spiral of about
two and a half turns.
THE DOG-FISH
(8) The rectum is the last part of the gut.
coecal or rectal glands open into it dorsally.
9
The
(9). The cloaca is the chamber into which the rectum
.as well as the urinogenital ducts open.
B.
The glands of the digestive sytem.
(i) The liver has I already
been described
earlier. The right lobe of it carries the gall
bladder. The bile duct leaves the ga.ll
bladder between the two lobes of the liver,
almost in the median plane. ] t is about half
an inch on the whole. It receives ducts
from the lobes of the liver.
(ii) The pancreas as described above lies in
the fold of the stomach amI intestine. The
pancreatic duct runs forward through the
pancreas, close to its Vf>ntral border,
enters the ventral wall of the intestine,
runs along it for about half an inch, and
opens just to the outer side of the line of
attachment of the spiral valve.
(iii) The rectal gland is a short thick-walled
tube lying in the abdominal cavity dorsal to
the rectum. .
4. DISSECTION OF RESPIRATORY SYSTEM.
Expose the gills on one side by prolonging the external,
ajertures upwards and downwards with scissors.
The Scoliodon breathes by lpeans of gills borne in
a series of gill-pouches. There are five pairs 'of such
gill-pouches, each of which is compressed antero- posteriorly
10
THE DOG-FISH
and communicates with the pharynx by a large
inter-branchial aperture ann with the exterior by a
narrow external branchial aperture.
The gills are a series of closely set, soft and highly
vascular folds of a mucous membrane radiating outwards
from the cartilaginous branchial arches and supported by
gill-rays. Each gill-pouch has two row~ of giJl-lamellae
one on its anterior and the other on its posterior
wall.
Successive gill-pouches are separated from one another
by stout fibro-muscular partitions, the inter-branchial
septa.
(i) Tho holobranch
or complete gill consists
of two sets of lamellae atta":led to a
visceral arch and its inter-branchial septum.
(ii) The demibranch or
of only a single set.
a half-gill c0nsist&
(iii) The pseudobranch is a rudimentary gill,
consisting of about half a dozen small
parallel folds, on the anterior wall of the
spiracle but in Scoliodon tho spiracle
bears no gill-lamellae.
5.
DISSECTION OF THE OIRCULATORY SYSTEM
(1). Pericardiai Cavity and Heart.
Pin the dog- fish on its back, on the dissectillg board.
Remove the middle portion of the pe(;toral girdle alld caref1tlly
open the pericardial camty. CZtt away the ventral wall
oj the cavity so as to expose it fttlly.
The Pericardial Cavity.
THE DOG-FISH
II
It is a median triangular cavity lying between the gills
with the apex directed forwards, and is almost completely
occupied by the heart.
Tpe heart is a single muscular tube bent on
itl'ielf forming four chambers, each separated from the
other by a transverse constriction.
(i) The sinus venosus is a triangular thinwalled
chamber elongated transversely,
attached along its whole length to the,
posterior and dorsal wall of the pericardial
cavity. Laterally it rec~ives two large veins,
the ducti Cuvieri and two hepatic sinuses
open into it in the postero.median line.
Anteriorly the sinus opens into the atrium
by a median aperture.
Expose the sinus venosus, press the 'ventricles slightly
forwards.
(ii) The
atrium (auricle) is a large sac
occupying the dorsal half of the pericardial
cavity. lts \\ aIls are thicker than those
of the sinus venosus. It is triangular
in shape, with its
posterior angles
produced into processes which project
laterally at the sides of thE' ventricle in its
natural position.
Push the globular ventricle to one side to expose the
auricle.
(iii) The ventricle is the most conspicuous
chamber of the heart. It has thick muscula~
walls, the inner surface of which is
produced into numerous muscular strands,
giving it a spongy tpxture. Ventrally the
ventrIcle is supported by the coracoid
cartilages.
12
THE DOG-FISH
(iv) The
conus
arteriosus
is
a stout
muscular tube running forwards from the
ventricle to the anterior end of pericardial cavity. The inner wa.ll of the
conus arteriosus is provided with two transverse rows of semi-lunar valves, one
dorsal and two ventro-Iateral in position.
(2). The Arterial System.
A. The Afferent Branchial Arteries.
The aif erent branchial vessels are almost su perficial.
Trace the continuation of the conus arteriostts towards the
anterior side, upto the posterior border of the hyoid ilrclz
where it bifttrcates. Follow other branches arisil:g from
it on both the sides to gills. Expose as much of thE' blood
vessels as pO$sible by removing the tissues coverintZ them,
and also the gills.
(i) The ventral aorta is the name given to the
anterior prolongation of the conus artf riosus.
Passing through the wall of pericardium it
extends along the ventral surface of the
pharynx right upto the posterior border of the
hyoid arch, where it bIfurcates into two
branches, the innominate arteries, each of
which again divides into two forming the
first and second afferent branchial arteries.
first
afferent
branchial,
the
anterior bra-nch of the innominate artery.
runs along the posterior border of thf' hyoid
arch and supplies the gill-lame lae of
hyoid.ean demibranch.
(ii) The
(iii) The second afferent branchial supplies
arterial branches to the anterior and posterior gill-Iam<lllae of the first branchial arch.
THE DOG-FISH
13-
(iv) The third afferent branchial arises a
little behind the bifurcation of the ventral
aorta and supplies the second branchial arelh.
(VI The
fourth and fifth afferent branchials
arise, almost equidistant from one another,
from the ventral aorta and run along the
outer borders of the third and fourth
branchial arches.
B. The Efferent Branchial vessels.
Insert 01'1e of the blades of a strong pair of scissors into
the mouth, and cut back horizontally along the left side
through the gill-arches to the last one_ Cut transversely
across the floor of the pharynx behind the heart from the
hinder end of the above inclsion. Continue to cut to the
correspondtng pomt on the opposite side. Turn the floor
of the mOllth w1th the heart over to the right stde. Wash the
floor thoroughly and carefully remove the mucous membrane
from the rooJ oj the mouth. Find the efferent branchtal
vessels rtmning inwards and backwards from the gill-slits,
and follow them, on one side, outwards to the gills and inwards to the dorsal aorta in the middle line.
The blood from the gills is collected by four loops of
blood vessels around the four branchial clefts on each side
Besides these a single vessel collects blood from the fifth
branchial cleft. The four loops are connected with one
another by short longitudinal connectives running across
the inter-branchial septa. Likewise the last vessel of th~
half-Ioop-, is also connected with the blood vessels of its
side (a part of the loop surrounding the fourth gill-cleft.)
The loops are further connected with each other by a network of longitudinal commissural vessels between
their ventral extremities.
:1.4
THE
DOG-I~ISH
(i) The efferent branchial arteries are nine in
number (eight formed by 4 collector loops and
the independent ninth). They run along
the anterior and posterior borders of the
five gill-clefts.
(ii) The epibranchial arteries are four on
each side. Each of the four collector loops is
continued into an epibranchial artery which
runs backwards and inwards to the mid-dorsal
line. The half-loop has no epibranchial of
its own.
tiii) The dorsal aorta is formed by the union
of the four pairs of epibranehials, (md runs
backwards along the w'hole lengf,h of the
body. Anteriorly it runs a Iittl' distance
and them bifurcates into two branches.
·c.
Th~
Arteries Of The Head.
The first efferent bra-nchial supplies blood to the head,
though a little is also contributed by the anterior end of
the dorsal aorta.
Clean the first ejJ erent bra1tchial careful! y and ty y to
locate its following branches. Trace them to the head region.
(i) 'J' he external carotid artery is a largo vessel
arising at antero-yentral corner of hyoidean
efferent. Anteriorly it travels to the hyoid
arch and divides into two branc'tes (a) the
ventral mandibular supplying the mandibular region and (b) the superficial hyoid
supplying the skin and sub-cutaneous tissues
over the ventral part of the hyoid arch.
15
THE D 00 -FISH
!lut'RkQ~e'TA\"
\
\
flllSl
EPleRA I'lt 1111\1-. __ _
SEtONO
E PI!?R.AMC.llli1L----
ttONO
'j
II
III
l-
e:
d;
TIURO
IZ
III
a:
III
....U101
Fig. I.-The Efferent bloorl vesselfl and the artetiev
of the head of the dog-fish_ The external carotid artery
that is shown at the extreme right, is actually on the
ventral surface, that is why it is often removed while
cleaning th~ent arteries unless the student is careful.
16
THE DOG·,FISH
(ii) The afferent spiracular artery a.rises a.t
about the middle of the hyoidean efferent. It
runs forwards on the outer side of the hyomandibular and epihyal cartilages, and then
bends inwards surrounding the spiracle. It
continues forward as the spiracular epibranchial artery across the floor of the orbit and
enters the cranial cavity through a small
foramen. Before entering the cranium
it gives a branch to eyeball, tho great
ophthalmic artery.
(iii) The hyoidean epibranchial artery arises
from the other end of the first efferent, a little
before its fusion with the second efferent to
form the first epibranchial. It run:, forwards·
and inwards to the posterior border of the
orbit where it is joined by th;> anterior
branch of the dorsal aorta and immediately
divides into two branches: the stapedial and'
the internal carotid. The stapedial artery
runs forwards and outwards and ellters theorbit where it gives branches, one supplying
the eye muscles, and the superficial tissues,
in the region above the auditory capsules,
and other supplying the anterior boundary
of the orbit. The former is called the inferior orbital while the latter is the superior
orbital.
The internal carotid passes inwards to the
buccal cavity and enters the cranium,
where it divides into two branchE'S, one of
which unites with its fellow of tl e opposite
side, while tbe other unites with the stapedial
to form the anterior and posterior cerebraL.
arteries.
THE DOG-FISH
17
D. The Dorsal Aorta and its Branches.
The dorsal aorta is formed by the union of the 4 pairs
of the epibranchial arteries. It runS backwards along
the whole length of the body, lying bene&th the vertebral
column in the trunk. In the tail region it continues into the
haemal canal of the tail.vertebrae as the caudal artery.
The following are the principal branches of the dorsal
aorta:
(i) The subclavian arteries are a pair of vessels
arising close to the union of the fourth
cpibranchial arteries, and run outwards
and backwards in the body wall and along
th{' hinder border of the pectoral girdle to
the pectoral fins, which they supply.
(ii) The coeliaco-mesenteric is a large median
artery arising from the dorsal aorta behind
the junction of the fourth pair of epibranchial arteries. It divides into two unequal
branches, (a) the coeliac that supplies the
stomach and liver etc., and tb) the anterior
mesenteric supplying the pancreas, the
intestine, and the rectum.
(iii) The lieno-~astric artery arises a short
distance behind the origin of the coeliacomesenteric. It is also a median blood vessel
giving off branches supplying the genital
organs, posterior part of the intestine and
the spleen etc. '
18
THE DOG-FISH
(iv) r£he posterior mesenteric artery is a small
median vessel arising from the aorta about
an inch and a half behind the Heno-gastric. It
runs backwards to the mesentery and the
rectal gland.
(v) The parietal arteries are a series of paired
vessels arising at iatervals along the whole
length of the aorta and supplying the bodywalls.
(vi) The renal arteries are small paired vessels
arising from the parietal arteriE's and supplying the kidneys which they enter from the
dorsal surface.
(vii) The iliac arteries are a pair of vessels
similar to the parietals, each of them extend
into the pelvic fin.
Note: If only one specimen has to be used for the
study of all the systems the dissection of the posterior
part of the aorta and its branches should be postponed
until after the dissection of the renal-reproductive organs
and the cloaca.
3.
The Venous System.
The blood in the dog-fish iB not returned by narrow
tubular veins but by large blood spaces or sinuses.
(i) The anterior cardinal sinuses collect
blood from the oui,er sidE' of the head and
the branchial region. Each is a large sinus
running backwards between the dorsal ends of
the gill-pouches and the muscles of the body
wall. Posteriorly it ent€'l'S the Cuvierian
THE DOG-FISH
sinus. It collects blood from the orbit, the
nasal region and the hyoidean region.
(ii) The inferior jugular sinuses are a pair
running parallel and ventrally to the anterior
cardinal sinuses, and each collects blood from
the sides of the lower jaw and the ventral
region of the gill-pouches. It commences
just infront of the postero-ventral margin of
the first gill-cleft and is situated beneath
the floor of the buccal cavity and pharynx.
Posteriorly it opens into the Cuvierian sinus.
('iii) The posterior cardinal sinuses lie close
together along the roof of the abdominal
cavity. They originate in between the kidneys, along the posterior region of which
only a median inter-renal vein represents
these, but in the anterior region of the
kidneys the dght and the left posterior
cardinal sinuses are distinct. In the region
of the oesophagus each of them expands
into a wide thin-walled sac opening finally
into t,he Cuvierian sinus.
t(iv) The hepatic sinuses a.re two l~rge thinwalled sinuses collecting blood from the lobes
of the liver. After traversing the whole
length of the right and left lobes of the liver
they open anteriorly into the sinus venosus
by two apertllres in the median line.
,{VI The Cuvierian sinuses are a pair, each of
which runs transversely, like its fellow of the
opposite side, passes through the pericardium
and opens into the basal angle of the sinus
venosus.
I
THE DOG-FISH
20
6. The portal
represented.
systems are two and quite
weIr
(i) The hepatic portal vein is formed by
the union of {lhe veins from the various·
parts of the alimentary canal. It divides
into three branches before entering into
the liver lobes.
(ii) The renal portal system consists of two
renal porial veins formed by the bifurcation of the caudaJ vein. which running
on the inner side of the kidneys, break up
into branches in the substance of the
kidneys. The blood is then collected by
the renal veins which open into the hinder
portion of the posterior cardinal :,inus.
6.
A.
DISSECTION OF THE RENAL AND REP··
RODUCrrVE SYSTEMS.
The Male:
After removi1tg the viscera dissect 0 if the peritoneum'
from the ventral. surface and expos~ the whole lengt~ of the'
kidneys. Examme. Cttt the W 01ifzan duct of one stde away
from the ventral surface of the mesonephros and trace it to
the cloaca. Also follow the vasa efferentia opening into the)
Wolifian duct.
(i) The kidney is mesonephric fully differentiated into genital (anterior) and r~nal (posterior) portions. The functional kidneys
lie, one on each side, closely adposl'd to one
another in the hinder end of the coelom and
covered by toughish peritoneum. The genital portion, which is almost devoid of excre,
THE DOG-FISH
21
tory tubulf>s, extends forward to the front
end of the body cavity beneath the peritoneum.
(ii) The testes are elongatE'd extending more
than half way back wards from the front end
of the roe 10m and covered by peritoneum.
The' fold of peritoneum suspending the testis
in the body cavity is called the mesorchium.
(iii) The Wolffian duct is well developed and is
thrown into an intricate series of coils overlying the genital portion of the kidney and
forming the vas deferens on each side.
~iv)
The vasa efferentia are minute tubules
which open into the anterior end of the vas
deferens.
(v) The seminal vesicles are simply enlarged
portions of the vasa deferentia on each side
before they open into a large triangular chamber, the urinogenital sinus, which finally
opens into the cloaca on an elevated urinogenital papilla.
(vi) The sperm sacs are two blind elongated
outgrowths of the urinogenital sinus, whose
function seems obscure.
Dissect away the sperm sac from vesicula seminalis and
follow it back to the urinogenital sinus. Cut open the
ventral wall of the ttrinogenital sinus and expose the
r:avity. Examine its parts.
22
THE DOG-F_[SH
(vii) The "ureters" are spcdal collecting ducts
developed in connection with the functional
l<idneys. From each kidney arise five collectmg ducts into which the renal tubules open.
The ducts join to form a large channel, the
"ureter", on each side, which opens into the
urinogenital sinus, alongside the opening of
the vesicula seminalis.
(viii) The Mullerian ducts are not functional,
but vestiges of them are found in the anterior
part of the coelom on the ventral side of th~
oesophagus.
(ix) The claspers are grooved elongations of the
pelvic fins which are inserted into the cloaca
of the female during copulation a'ld, thus,
the sperms are transferred to the femr.le.
(x) The siphons are muscular sacs lying beneath
the skin of the ventral surface in the pelvicregion. Posteriorly these sacs extend as siphontubes, each of which opens into the groove of
the clasper of its side. The use of the siphons
seems to be obscure, though it has been
ascribed the function, by squirting out the
contained sea water, of flushing spermatozoa.
accumulated in the claspers into the femalecloaca.
B. The Female.
Remove the viscera and
Observe the ovary and the
opening of the oviducts near
liver, immediately beltznd lite
of the ovrdttcts to the cloaca.
dissect off the pentoneu11t.
kidneys. Locate the anterior
tlte suspensory ligament of the
pericardzal wall. Follow one
THE DOG-FISH
(i; The kidneys are paired each showing the
same differentiations into an anterior and
posterior portion.
(ii) The ureters commence in the anterior part
and continue backwards and in the region
of the functional kidney each dilates and
joins its fellow of the opposite side forming
a common duct opening into the urinary
sinus, a triangul&r chamber. This sinus
opens into the cloaca at the tip of the
urinary papilla.
(iii) The ovary is only single in the mature fish.
It is apparently median in position
suspended in the body cavity by a fold
of peritoneum, the mesovarium. It is
actually the right ovary.
(iv) The oviducts are the well developed
Mullerian ducts, each of which is a stout
tub,:,. The anterior coelomic opening, of
these have coalesced to from a single wide
aperture, the oviducal funnel. From the
common aperture each oviduct narrows
slightly and passes backwards at the sides
of the coelom to the cloaca. At about one
third of the way down its anterior end
pach oviduct swells out to form the oviducal
gland which is responsible for the secretion
of the egg case. Behind the glands the
oviducts are large and dilatable with
longitudinally folded walls. Posteriorly
they unite and open by a large median
aperture into the dorsal wall of the cloaca.
Expose the cloacal chamber by cutting in between the
pelvic fins and note.
THE DOG-FISH
(v) The cloaca is a shallow depression between
the pelvic fins. In the female there are
three openings into it, the rectum infront,
the genital aperture in the middle and
the urinary sinus behind.
7. DIS.::lEOTION OF THE SENSE ORGANS.
A.
The Orbit and the Eye Muscles.
Dissect away the eyelids of one of the eyes and remove
the skin surroundillg it. Examine the followillg :
1. The eye ball is almost hemispherical in shape. Only
its outer surface is flat. It is held in position by si'l: eye
muscles, and a cartilaginous stalk, the optic pedicle.
The stout optic nerve mayalso be seen crossing the
orbit and entering the eye ball.
2. The eye muscles consist of six narrow muscular j
bands which arise from the wall of the skull and are
inserted into the eye ball.
(a) The recti muscles are four in number
arising from the posterior end of the or bit.
(i) The superior rectus rnns outwards and
upwards and is insertcci on the dorsal surface
of the eye ball.
(ii) The inferior rectus runs outwardE and
downwards to be inserted on the ventral
surface of the eye ball.
(iii) The anterior rectus runs forwards and is
inserted on the anterior surface.
THE
DOG-l!'ISH
(iv) The posterior rectus runs backwards and
is inserted on the posterior surface.
(b) The oblique muscles are two and arise
from the anterior angle of the orbit close
together.
(i) The superior oblique is inserted on the
dorsal surface of the orbit infront of the
insertion of the superior rectus.
(ii) The inferior oblique is inserted on the
ventral surface of the eye ball.
3.
The Nervous Supply of the Eye Muscles.
(i) The oculo-motor or the third cranial
nerve enters the orbit and divides into
branches that supply the antE'rior rectus,
the superior rectus, the inferior rectus
muscles as well as the inferior oblique
muscle of the eye ball.
(ii) The trochlear or the fourth cranial nerve
arisE'S from the dorso·lateral surface of
the mesencephalon, and on entering the
orbit supplies exclusively the superior
oblique muscle of the eye ball.
(iii) The abducens or the sixth nerve is a slender
nerve arising from the medulla oblongata,
and it innervates the posterior rectus
muscle on entering the orbit.
THE DOG-FISH
B.
Dissection of the Ear.
Clean the hinder end of the skull so as to expose the
auditory capsule fully which can be easily located by three
prominent ridges on the dorsal smface. These ridges lodge the
three canals of the internal ear. They can be even sem through
the cartilage. Having located these hold the specimen in
your left hand and carefully scrape away the cartilage with
a sharp scalpel 1tllt~l the several parts of the auditory
orgnas are exposed. The dissection is not at all difficult
because the parts of the internal ear can be seen from outside
owing to the transpareilcy of the cartilage. The thing needed
is absolttfe care. After exposing the canals and the vestibule
study it in situ. Then remove the entire organ, keep in
a watch glass, study and sketch.
1. The vestibule is a laterally compressed sac
differentiated by a constriction into a dorsal ch,p,mber,
the utriculus and a lower chamber, the sacculus, the
posterior end of which forms an out-growth, the lagena.
From the sacculus arisE's a narrow tube, the ductus
endolymphaticus which runs upwards and pierces the
cranium.
2. The semi-circular canals are three tubular loops
opE'ning into the utriculus. These canals are mutuaUy
at right angles one being horizontal, the horizontal
canal, and the other two vertical, the anterior vertical
canal and the posterior vertical canal. At one end
where it joins the utriculus each semi-circular canal is
swollen out to form an ampUlla.
C.
The Sensory Ampulla.
At the anterior end of the snout there are a number of
small openings, as mentioned earlier.. Squeeze the nead of
the dog-fish provided so as to make water exude out, and
thus render the openings vis~ble. Cut off a rectangluar bit
of the tissue along with the skin and muscles almost a ce1Z~
THE DOG-FISH
timeter deep. Make sure before wtting that the area contains
the openings of the canals. Carefully identify the masses of
the ampullae and the nerves in connection with them and then
tease them out so as to separate the ampullae, mount ana
examine under microscope. Sketch.
The ampullae are specialized neuromasts sunk below
the skin and found in groups on the dorsal and ventral
side of the head. Each ampulla is an elongated tube'
opening externally by a pore in the skin, and ends in
radially separate ampullary sacs, lying deeply beneath
the integument. The ampullary sacs are innervated
below.
8.
DISSECTION OF THE CRANIAL NERVES.
The first cranial nerve, the olfactory nerve, consists
of a group of separate fibres, which arise from the olfactory cells in the olfactory organ and direct]y pass into
the olfactory lobes of the brain. The second or the optic
nerve, as described earlier, innervates the retina. Before
entering the orbit it forms the optic chiasma. The third
or the oculo-motor, the fourth or the trochlear and the
sixth or the abducens, supply the muscles of the eye (see
page 25). The eighth or the auditory is also a small nerve
directly passing from the medulla obiongata to the
auditory capsule. The fJIlowing is the description of
the fifth or the trigeminal, the seventh or the facial, the
ninth or the glossopharyngeal and the ter.th or the
vagus.
Remove the skin from the 1tpper surface of the head; now
remove the eye ball clean tlte tissues carefully and note a
prominent nerve running across the dorsal margin of the
orbit. Tlzzs is the ophthalmic nerve formed by the
ophthalmic branches of both the fifth and the seventh. Trace
it bothways anteriorly as well as posteriorly to the places
of its supply and origin respectively.
THE DOG-FISH
28
The fifth, seventh and eighth nerves arise very close
together from the side of the medulla oblongata, at its
widest part, opposite the posterior part of the lcrebellum.
The hinder-most is the eighth and it passes straight to the
auditory capsule, while the fifth and the seventh nerves
;pass outwards through the skull-wall by a foraman at the
posterior and inner angle of the orbit,.
(i) The fifth or trigeminal
branches.
nerve
has three main
(a) The ophthalmic branch, as already noticed,
arises from the anterior border of the
root of the fifth nerve, close to th'l brain.
It runs forwards and backwards for about
a quarter of an inch ",nd then ,'merges
out into the orbit, where it runs along
with the branch of the seventh. The main
stem of the fifth nerve appears as a broad
ribbon-like band entering the orbi<:;, near
the outer margin of which it separates into
the maxillary and mandibular bfl1nches.
Dissect the t~ssues aif and trace the nerves across the
floor of the orbit, and follow its branches to their distribution.
(b) The maxillary branch is the anterior of
the two. At the anterior border of the
orbit it turns over the upper j ,tW and
divides into branches which innervate
the region of the upper jaw.
(c) The mandibular crosses the upper jaw,
curves round the angle of the mouth and
29
THE DOG-FISH
runs along the lower jaw. It is very
superficial, just below the skin, at theplace where it crosses the upper jaw.
(ii) The seventh or facial nerve. The root of theseventh arisE's immediately behind the fifth and
divides into four main branches.
('a) The ophthalmic branch pentratcs the orbit
close to th(' similar branch of the fifth :o.nd
runs along its side to the cutaneous sense
organs on the snout.
-m
OPHTHALMIC
Yf1 m ~ V&vn: IX X
LATERAL X
\ \ ~!!~:-:;';f-~f'--::::~:::::::::~-::::::':::::
\
\'
,
\
\,
•
,
I
I
'
I
.-
,
eUCCAl'iII'" ...
MANDIBULAR V, ...
I
HYOID
PALATINE 'al
I
Fig. 2.-The cranial nerves of the dog-fish.
The main stem of the seventh nerve enters the orbit
immediately bchtnd the fifth and divides into three branches.
Dissect ottt each of them to the place of its innervation.
(b) The buccal branch arises from the main·
root and runs along the maxillary and
mandibular on the floor of the orbit.
(c) The palatine branch is a slender nerve
which crosses the floor of the orbit.
.30
THE DOG-FISH
(d) The hyomandibular branch which lies
in the posterior wall of the orbit and passes
in the direction of the spiracle. Looping
around the spiracle the main ramus of
the nerve continues closely beneath the
skin to the lower jaw as the external
mandibular branch and another branch
runs down the hyoid arch as the hyoidean.
(iii) The ninth or glossopharyngeal nerve arises from
-the medulla oblongata closely behind the eighth and
innervates the first gill-cleft over which it divides into
a pre-trematic branch and a post-trematic, the
former passing up and the latter passing down the first
branchial arch.
(iv) The vagus arises from the side of the medulla
oblongata behind the ninth by a series of rootlet,s. The
nerve has three main branches:
(a) The lateralis branch, quite prominent and
long, runs posteriorly supplying the lateral
line receptor organs of the trunk.
(b) The visceralis branch continues backwards
into the body cavity where it gives off
branches to th~ heart and viscera.
(c) The branchialis branch consists of four
su19sidiary nerves supplying second to the
fifth gill-slits, each nerve dividing into a
pre- and a post-trematic branch, the
latter running right down the gill arch.
9. THE DISSECTION OF THE BRAIN".
The dog-fish lives in deep seas and as such depends more
,upon the sense of smell than upon the sense of sight.
Also, the powerful movements during swimming neces-
THE DOG-FISH
sitate efficient control of muscular activity. The bmin,
therefore, is specially modified to accommodate these
activities. The olfactory lobes and the cerebellum are
well developed, whereas, the optic lobes are not enlarged.
For convenience the brain should be dissected after the
dissection of the cranial nerves. Remove the skin of the head
and slice off the clrtilaginous covering of the cranium exposing
the brain fttlly. The brmn ocwpies the cranial cavity
~llmost fully. Observe the following parts.
(1)
The fore brain is represented by
(a) The relatively enormous olfactory lobes which
are closely applied to the olfactory organs.
The pallium merely consists of small
paired protuberances on the dorsal surface
of this region.
(b) The thalamencephalon narrows from the
wide anterior portion. Dorsally it carries
the slender pineal stalk terminating in
the pineal body lying closely against
th~ roof of the cranium. The greater
part of its dorsal surface is occupied by
the anterior choroid plexus. Ventrally
the thalamencephalon has the optic chiasma and a relatively large pituitary
body, the latter consisting of the infundibulum, hypophysis and the accessory
lobi inferiores of the infundibulum.
(2) The mid-brain is very moderately developed.
Dorsally aI:e two rounded prominences which project
somewhat beyond the sides of the brain. These are the
,optic lobes (corpora bigemina). Ventrally the crura
cerebri are hidden by thb posterior part of the pituitary
>body.
(3) The hind-orain has a very prominent cerebellum
.that projects forwards, to some extent covering the optic
THE DOG-FISH
lobes, and backwards over the roof of the fourth ventricfer
The cereb"Uum continues in the medulla oblongata that.
is very well developed.
(4) The Ventricles.
Cut a median longztudt1lal section of the enttre brain
and examine the cavities of the brain that are spaciolts.
The cavity of each olfactory lobe is known as
rhinocoel which communicates wi\h the lateral
ventricles behind. ThE' lateral ventrIcles open into
the large third ventricle behind, each by a foramen
of Monro. The cavity of the third ventricle extends
into the infundibulum of the pituitary body and also
into the base of the pineal stalk. The optic lobes have
optocoels within them. The fourth ventricle is the
cavity of the medulla into which also opens the cavity
of the cerebellum. A common space connecting the
third and fourth ventricles, into which the optocoels also·
open, is called the iter.
10. 'THE SKELETAL SYSTEM.
Preparation of the Skeleton.
Take a fairly large sized dog- fish well preserved in formalin. The skeleton zs cartilagin01tS as such is ltable to be
damaged easily. Remove the skzn and muscles etc. carefully. Dip the specimen in hot water once or twice to loosen
the connective tissues and then scrape hghtly. An lld tooth
brush will be of immense helP in bmshing away the Jissues.
A great care should be taken particularly when cleaning
the skull and visceral skeleton. Whw the skeleton is thoroug-My cleaned -up, keep it in week formalin.
THE DOG-FISH
33
t>
A. The Vertebral Column.
AJter cleaning the vertebral column thoroughly note the
attachment oj median fins with it, detach the med~an fins
later: Study a portion oj the column' Jrom olte side specially noting the arrangement oj the vertebrae and sketch:
Thn~ cut transverse and sagittal sections oj ihe same 'and
complete your study and sketch.
.
1. The centra surround the notoohor}l, and are short
cylindrical bodies of cartilag~ hollowed oU,t at either
ends, ie. the vertebrae are amphicoelous. The notochord
is constricted in the middle of the centrwp.),mt ~s. greatly
dilated in the intervertebral spaces.
.
.
I
The centra are strengthened by ca:Icified fibro-cartilage
developed as four wedges which traverse the body of 'the
centrum from its periphery almost to the centre t':!us
giving rlse to a curciforum figure, "Maltflse cross," which
can be seen in a trans ver3e sectiu-n of the cen tru m through
the middle.
2.
The neural- plates are a series -of hexagonal
of cartilages forming the sides of neural arches;the spaces between the . consecutive vertebral neural
plates in contiguous vertebrae are occupied by the
intervertebral neural plates.
~lates
3. The neural arches lie dorsal to the centrum
enclosing the spinal cord. Each arch is formed of elements
of two kinds viz. (i) the- neural processes, the blunt
bases of the neural arches projeoting upwards from the
sides of each centrnm, and (iij the neural spines, a
series of median nQdul@s of cartilage completing the
n:mral arch above.
4. The transverse processes are a pair of blunt
'lOrizontal projections on each side of the lower surface of
3
34
THE DOG-FISH
(j
'Jentrum, in the trunk region which bear at their anterior ends movably articulated cartilaginous ribs about half
a):l inch in length.
.•• 3
5. The haemal arch is found in the vertebra of
the tail region. Here the transverse processes, instead
of projecting laterally, are bent inwards beneath the
centrum and meet and fuse in the mid-ventral line to
form an arch, the haemal arch, the ribs, as such, are
absent. Each haemal arch enclo8ing the haemal canal
is produced into a backwardly directed and flattened
haemal spine.
B. The Skull
The skull in the dog-fish (lonsists of a brain hox with
an incomplete roof, a pair of thin olfactory capsules
anteriorly, a pair of stout auditory capsules po:;teriorly,
and at the sides are the shallow orbits. Because the
cartilaginous condition is retained into adult life it is
called a chondrocranium.
The brain box or cranium is a simple cartilaginous
cylinder open infront and behind. The roof is arched
and the floor flat. Anteriorly it gives off three cartilages
which are prolonged forward to fOJrm the rostruOl.
Examine the various parts of the cranium in the following order. Sketch.
1. The occipital region forms the posterior part
of the cranium enclosing the large median opening, the
formen magnum on its posterior side. On eit,her ,side
of the formen magnum there is a prominent cccipital
condyle. On the roof of the oecipital region there is a
prominent median ridge, the ocdpi~al crest. External
to the occipital condyles on either side lies a large
foramen for the exit of the tenth nerve, the vagus.
\
'l.'HE DOG·Fl;
",,>Ji•
::::
....0CIl
~
~
<T.I
<6...
<lJ
<:.>
til
'>
~~
:i<l\
,.._..
,,'"
._
II"
~Z
<T.I
;-=:
\
"'d
-
~
.,"
... 01
~
cil
~
<T.I
<:;::I
bo
0
0:1
"0
!:;
...c:
...,
CD
.....0
~
.!<I
<T.I
Q.>
....
~
.....0
e::
<lJ
-'>...,...
cil
<lJ
cil
....::
\
C'6
bO
ri;
THE DOG-FISH
2. The auditory region consists of the auditory
capsulefS and the pa rt of the cranium they are fused with.
'rhe lsrge latE'rally projected auditory capsules lodge the
auditory organs, as such, the outer surface ::"hows three
prominenJ ndges lodging the three semi-circular canals
of the ear, which ean usually be seen through the
cartilages.
On the roof of the cranium lying between the two
capsules, there is a marked depression, the parietal fossa,
with a pair of apertures on each "ide of its posterior
part. The posterior pair are the fenestrae or the openings of the perilymphatic spaces of the two capsules,
whereas, the an~erior are a pair of apertures through
which the endolymphatic ducts (aqueduct>us vebtibnli)
of each internal ear piprces the cramum .
.
3. The orbit lodges the eye ball and its lliJscles.
The dorsal bound a ries of the orbits are formed "Y the
supra-orbital crests, which are prominent cl;rved
ridges of cartilage running along the sHes of the skull
from thp olfactory to thp auditory cap:.uli's. Fnrther
the boundaries on thp othpr sides are marked by t~e
pre-orbital cartilages. which are slender cartilag~s
arising frolll the roofs of each olfactory capsule Ju"t
infront of the orbit', and curvcd backward partially
t'ncircling the orbit, and the post-orbital cartilage
on cal' h SIde arit:les from the a udi tory capsule and cun es
forward along the uppl:'r border of the orbit.
The Foramina of the Orbit.
(i) The
orbito-nasal foramen is a small
circular aperture at the anterior inferior
angle of the orbit.
~ii)
The optic foramen is a large apertlll'e for
the optic nerve at about tIll:' middle of the
orlits length near its ventral border.
1'RE DOG-FISH
37
iii I The foramen for the third nerve is a
small hole in the inner wall of the orbit
behind and above the optic foramen.
lV) The foramen of the fourth nerve is a
small hole vertically above the optic foramen
often pushed a bit pogteriorly.
(v) The foramen of the fifth and seventh
nerves is a large hole immediat(jly infront
of the auditory capsule. The sixth nerve
also enters the orbit through the '>ame
opening.
(vi) The aperture of the inter-orbital canal
is a cireular opening infront of the large
aperture for the fifth and sE'venth nerves.
The inV'r-orbital canal traverses the base of
the skull and places the orbital blood sinuses
of the two Hides in communication.
(vi.) The foramen for the spiracular epibranchial artery into the ('mnium lies slightly
anterior to the- (vi).
<viii)
The foramen of the hyoidean a'rtery lies a
little infront of and a little below the
aperture of the inter-orbital canal.
I)X) The foramina for the ophthalmic branches
of the fifth and seventh nerves are two
.. eparatp apertures near the posterior end
of the orbit just mfront of the auditory
f'apsule and above the foramE'n for the main
hranches of the fIfth and seventh nerves.
38
THE
DOG-FISH
4. The olfactory capsules are two large oval cartilaginous cups at the anterior end of the skull, firmly united
to the cranium in the adult condition. A thin median
cartilage, the internasal septum separates the two
olfactory capsules from each other. The cranial roof in
this region is complete, there being a large anterior
fontenelle covered over by a sh!'et of connective tissue.
Within each olfactory capsule there is a large opening
leading into the cranial cavity for the entrance of the
olfactory nerve .
.
5. The rostrum is formed by three cartilaginous
bars. In front of the anterior fontenelle arises a pairof dorso-Iateral cartilages one from the roof of each
olfactory capsule; these run forwards to converge and
meet in the front with a median ventral canilage which
projects from the base of the cranium.
6. The floor of the cranium is broad and flat and
bears towards its hinder end two obliquely transverse
grooves, the carotid canals. It narrows considerably at
its anterior end where the olfactory capsules are attached.
Immediately behind the olf!tctory capsules lie two large
and prominent articular surfaces for the attachment of
the ethmo-palatine ligaments of the upper jaw while
infront of these articular surfaees lie the anterior opening
of the orbito-nasal canals.
7. The articular surface for the hyomandibular
cartilage is a concave depression on the side of the hinder
end of the skull, below the auditory capsule.
C.
The Visceral Skeleton.
The visceral skeleton is made up of a series of
visceral arches which develop in the pharyngeal wall
between the visceral clefts. Typically each visceral arch
is an incomplete ring of cartilage consisting of 8 basal
piece in the mid-yentral line, with which articulate a.
THE DOG-'FISH
39
series of pieces on each side extending upwards almost
to the mid-dorsal line. It' is clear, therefore, that ths
skeletal arrangement is independent of the chondrocranium
and strictly speaking is not even part of the axial skeleton,
though for convenience it is usual to consider it to be so.
Tn the dog-fish seven visceral arches are developed,
and it is the first two which warrant special attention.
(1) The mandibular arch is the first pair bordering
the mouth and modified to form the jaws. It has lost
its original arch .form and consists of four pieces of cartilage, two on each side of thp. mouth and all joined
by ligaments. Laterallyan upper jaw, plato-petrygoqpadrate bar, above and lower jaw, Meckel's cartilage,
below meet behind the mouth. The two rami of the
upper and lower jaws meet anteriorly in the mid-line.
The jaws have no direct connection with the chondrocranium, which is provided by the second or hyoid arch.
(2) The hyoid arch is a loop of, cartilage made up
of five pieces.
(i) The basihyal is a median piece of cartilage
lying between the rami of thf' lower jaw.
It is rounded anteriorly and produced behind
into two horns which are attached by
ligaments to the dorsal surfaces of the
ceratohyals.
(in The ceratohyals are two cartilages each
of which is long and slender and runs
forwards and inwards in the floor of the
mouth articulating with the basihyal at its
lower end. Each carries gill-rays along its
posterior border and lies in the anterior
walls of the gill clefts. ,
THE DOG-FISH
(iii) The hyomandibulars are two cartilage::.
,
dorsal to the ceratohyals. Each hyomandibular is a short stout rod fitting at its upper
end into depressions in the auditory capsules.
of the chondrocranium to whirh they" are
attached by ligaments. These" cartilages
are the sole direct skeletal connections between
the jaws and the cranium forming on each
side the suspensorium of the' upper and
lower jaws.
(3) The branchial arches are the remallllllg five,
visceml arches lying in relation with the branchial clefts.·
They ,gradually diminish in size antero-posteriorly. Each
arch is ma~8; up of a variable uumber of cartilaginous
pieces. Observe their numbers and note.
0"
(4) The labial c~rtil~ges are two pairs"
~lender ,
cartilaginous rods in the folds o£. the skin at t 11(' sides
of the mouth.'
."
D.
1.
The Skeleton of the Fins.
The Median fins.
The skeleton of the two dQrsal and the ll,ledian ventral
fins consists of a seril's of cartilaginous rods called
somactidia or pterygiophores, bearing dista~ly a double
..cries of horny fin-rays, or c;erat6trichia. A wide strip
of ligamentous tissue connects the somactidia of the
fjn with the vertebral column.
Count the number of somactidia an{/, note.
The other median fins are built on the same plan as
the above described. Only in the c<1u,dIt1 fin, somactidia
are absent. The noma1 and haemal sp~pes of the vertebral
column are elonga,tet;l and flattened to support the dorsal
lmd ventral lob{'" of the fin.
THE DOG-FISH
2.
The Paired Fins.
-\.
The Pectoral region.
-t-l
(i) The pectoral girdle consists of two halfloops of cartilage fused in the mid· ventral
line and free at thc dorsal ends. Each haH
of the girdle is a scapulo-coracoid-the
dor,,;al one is the tapering scapular region
and the ventral one is the broaa.er coracoid
region In the mid-ventral portion of the
girdle, at the junction of two' coracoids, is
a well defined depression, the pericardial
depression lodging the perieardium and th£'
heart in life.
(Ji) The pectoral fin articulates, with the girdlt
by the basal cartilages the pro, meso,
and metapterygium.
Arising distally
from these are the radial cartilages or the
cartilaginous fin.ruys. Each consists typically of three pieces, thus, forming three
rows, the proximal contains pieces of varying
sizes but uniform arrangement, the second
and third rows are not uniform because the
pieces forming these ttl.ke the form of interfitting, polygonal plates. The periphery of
the fin is formed by an upper and lower
series of horny fin.rays or dermotrichia.
B.
The Pelvic region.
[i] Thf' pelvic girdle consists of it simple bal
of cartilage, the ischia-pubic bar embedded
transversely in the ventral body muscles,
infront of the cloaca.
42
THE DOO - FISH
(ii) The pelvic fins articulate with the ends of
the pelvic girdle. Each is made up of a,.
single basal cartilage, the basi pterygium,
supporting a fairly uniform series of radials.
As in the pectoral fins the peripheral portions
of the fins are formed of dermotrichia. In
the malf" the two fins are joined together
posteriorly and in connection with each
basipterygium there is a grooved, backwardly
directed cartilaginous prolongation which
forms the axis of the intromittent organ
or clasper.
CHAPTER
II
THE FROG.
Dissection of the Cranial Nerves.
There are ten pairs of cranial nerves in the frog. Of
these the fifth, the seventh, the ninth and the tenth are
branched and have long courses and take some time to
dissect the rest have short courses and are very easy
to dissect.
Remove the skin from the head. Remove the nasal by
scraping 0 if and expose the olfactory cavity. Remove theeyelids and cut along the dorsal margin of the eye very
carefully. Press the eye ventrally and examine.
(i) The olfactory nerves are small nerves
emerging out of small foramina in theethmoid bone. By removing the ethmoid
bone they can be traced directly to theolfactory lobes of the brain, from which
they arise.
(ii) The optic nerve will be visible on pressing
the eye ventrally, as a stout nerve entering
the eye ball. After forming the chiasma it
emerges out of the cranium and enters theeye ball.
(iii) The oculo-motor is the third cranial nerve and
supplies four of lhe muscles of the eye ball,
the rectus superior, rectus inferior, rectUfr
medialis and obliques inferior. It emerges:
from the cranium through a small foramen
near the opening for the optic nerve.
(iv) The trochlearis or the fourth nerve is a
small nerve leaving tbe skull through a
43
...1.4
THE·FROG
special foramen a little above the optic nerve.
It innervates the superior oblique muscle
ofth(> eye.
, v) The trigeminal 'or the fifth nerve is one of
the largest cranial nerves of the frog. It is
divided into two branches, the ophthalmic
and the maxillo-mandibular which divides
mto two branch(>s bhe maxillary and fhl
mandibular "
I
V OPHTHALMIC
V TRIGEMINAL
VllMANDIB\.,LAR- - -~/ -
----..,L_ _ _~
VII HYOIDEf\N- - - -IX.GLOSSOPHARYNGEAL
Fig. 4.-The fifth, seventh, ninth and tenth cranial
nerves of the frog.
As soon as the eye ball is pressed towards the 1·entral
side a very delicate rtave 'It:ill be seen running across the
dorsal margin of the orbit. ThIS is the ophthalmic branch of
-the fifth. While dissecting this ,special care should be taken
as it is easily removed along with other tissues. NO'll} trace
it wwards to its place I)f origin. Now remove the eye ball
completely. Tlti'i will expose the maxillary brarch of the
fifth crossing the orbit alung its 1'entro-posterior margin.
Locate the mandibular branch of the fifth that lies posterior
to the maxillary branch. Dissect it up'wards to where both
meet. Trar:e tlie maxilla-mandibular upto its Place of
'lvigin..
THE :FROG
45
(a) The ophthalmic arises from the anterior border of the' root of the nerve close to thE'
brain and runs along the dorsal side of the
orbit, passes into the nasal eapsule of its side
and innervates the skin of the anterior side
of the head.
(b) The maxillo-mandibular runs outward
and backwards behind the eye. It soon
divides into the maxillary and mandibular.
The maxillary enters the orbit, crosses it. and
innervates the region of the upper jaw. Each
mandibular turns posteriorly, runs a little
distance behind and loops anteriorly crossingthe af\gle of the jaws and runs along the
mandibles and. supplies .the skin of thelower jaw,
To expose and to trace the course of the mandibular thefree end of the squamosal has to be removed.
(vi) The abducens or the sixth nerve emerges'
through the same opening as the fifth 'and
innervates the external rectus muscle of'
the eye.
(vii) The facial or the seventh nerve arises from
the medulla closely behind the fifth and
leaves the cranium along with the same.
It soon divides into two branches the palatine'
and the hyomandibular.
Remove the muscles of the eye complet,ely.
(a) The palatine will be seen crossing the floorof the orbit just above the mucous membraneof the mouth. The main nerve passes on
to the nasal chamber and the anteriorportion of the roof (If the mouth.
THE FB,OG
(b) The hyomandibular runs outwards and
then backwards around the auditory capsule
and just at the angle of the jaw it divides
into a hyoidean supplying the hyoid
apparatus, and
internal mandibular
supplying the skin and muscles of the region
of the lower jaw.
(viii) The auditory or the ei~hth nerve is a short
nerve entering directly the auditory capsule.
(ix) The ~lossopharyn~e:al or the ninth nerve
arises from the side of the medulla from
the group of roots in common with the tenth.
These emerge from the skull through a
foramen in the exoccipital, external to
the condyle.
To expose the glossopharyngeal and the vagus the supra:scapula has to be removed. Cut 0 if the muscles binding the
suprascapula and cut it from its junction with the scapula
Observe the stozel second spinal nerve, brachial, going
..to the arm.
A short distance after emergence the t,runk of the
lossopharyngeal forms a ganglionic swelling where it
, ives a delicate branch that joins the hyomandib11lar of
the seventh. Later the glossopharyngeal runs downwards
.and backwards turning towards the anterior side, a little
behind the angle of the jaw. It runs ventrally along the
lower jaw and innervates the to~gue and the pharynx.
(x) Tht> va~us or thf' tenth arises al,mg with the
ninth and on emergence passes blLckwards
and gives, branches to the larynx, oesophagus,
stomach, lungs and l).eart etc.
(Note: The hypoglossal or the first spinal nerve that
runs almost parallel to the glossopharyngeal in the region
.of the lower jaw and supplies the tongue and several
THE FROG
47
muscles attached to the hyoid often confuses a studam.
If so, care must be taken to trace the hypoglossal, upto
the place of it!:! spinal origin).
2. THE BRAIN.
The dissection of the brain of the frog, though already
done in the intermediate class, is included here only
by way of revision. Structur.1lIy it is quite simple and
without much specialisation. It will be of immense help
to examine the brain and its various cavities.
Scrape 0 if the fronto-parietal bones of the cranium carefully and expose the &r.ain as fully as possible. As the brain
is quite soft and pulPY take care not to injure it.
Do you know the following parts?
1.
The fore-brain.
(i) The olfactory lobes.
(ii) The cerebral hemispheres.
<iii) The median furrow.
(iv) The thalamencephalon.
(v) The pineal body.
(vi) The optic chiasma.
(vii) The pituitary body.
2.
(viii) The anterior choroid plexus.
,
The mid-brain.
(i) The optic lobes.
(ii) The crura cerebri.
lb
THE FHOG
3.
The hind-brain.
(i) The cerebellum.
(ii) The posterior choroid plexus.
(iii) l'he medulla oblongata.
4.
The Ventricles.
Cut the brain t'ttto two halves, by a sharp !mire or a;
'yazor blade, alO1i g the lateralltne. attd note the following.
), The rhinocoel.
(ii) The lateral ventricles.
(iii) The third ventride.
(iv) The foramen of Monro.
(v) The optocoel.
(vi) The fourth ventricle.
(vii) The iter.
CHAPTER
III
THE LIZARD (V ARANUS)
The living reptiles include the lizards and chamaeIeons ; the snakes, tortoises and turtles; the tuataras ;
and the crocodiles and alligators; of these some lizards
such as the varanus (varanidae), the uromastix
(agamidae) or gecko (geckonidae) are examined as
representative of the class. The following is the description
of the varanus, but it can safely be used for the study of
uromastix or ordinary wall lizard (gecko), as the case
may be.
1.
EXTERNAL FEATURES.
Examine the specimen placed before you. Notice that
the body is covered with scales like that of the dog-fish
and that the body has a distinct neck supporting a comparatively smaller head. What is the difference between
the scales of a dog-fish and those of a reptile? What
type of a neck, if at all, was present in the frog or the fish?
The caudal region in the lizard is quite long. The body
is· elongated supported by two pairs of short limbs, of
approximately equal siz e.
a. The head is triangular in shape with apex directed
forwards.
(i) The mouth is a wide slit·like aperture running
around the anterior border of the head.
49
50
THE LIZARD
(ii) The nostrils are minute apertures situated
above the anterior ~xtremity of the head.
What types of nostrils are met with in the fishes?
The eyes are large, at the sides of the head,
provided with two-the upper and the lowermovable and opaque eyelids. A transparent
nictitating membrane is also present which lies
foldt'd at the anterior angle of the orbit when
withdrawn. (In gecko the eyelids are' fused
forming a transparent covering as in snakes).
(iv) The tympanic membrane is a circular,
brownish patch of skin on each side, behind
the eye slightly sunk below the general surface
of the skin.
b. The trunk is elongated flatter ventrillIy and
('onvex dorsally. It is supported by two pairs r,f pentadactyle limbs.
(i) The fore limbs arise from the trunk just behind the neck. Each consists of the upper
arm (brachium), the fore arm (antibrachium), and the hand having five clawed digits,
the first digit (pollex) is the smallest.
(ii) The hind limbs are situated towards the end
of the trunk more towards the ventral side.
Each has a thigh (femur), shank (crus) and
r. foot (pes) having five digits with horny
claws, the first or hallux is the smallest.
(On the under side of the manus and pes in
gecko, leaf-like adhesive pads are present.
The surface of the pads on each is <::ivided by
a. series of transverse plates. They help them
clim b smooth vert,ical
surfaces. In the
uromastix and var~he limbs are usedfor
digging).
51
THE LIZARD
(iii) The cloacal aperture io; a slit-like transverse
aperture on the ventral surface of the tail.
c. The tail is dorso-ventrally compressed structure,
thick in front and gradually tapermg to a narrow posterior extremity_
(Some lizards break off their tails very easily to keep the
attention of their enemie::. engaged to it while they escape.
The tails regenerate later on. Is the process painful to
the arumal '! If not, how does it happen ?)
Draw neat diagrams showing the dorsal and ventral
views.
2. DISSECTION OF THE COELO}I
A~D
VISCERA
Lay the animal 01t its back and Cltt open the body
.cavity by a mid-ventral incLsion. .Vote the pQsition of the
organs of the body cavity.
(i) The coelom or the body cavity is a cylindrical
,cavity lined by thin glistening membrane, the peritoneum
.and lodging the viscera.
(ii) The heart is triangular in sh:1pe, situ:1ted in the
middle of the anterior portion of the body cavity. It is
enclosed in a transparent, pericardium.
(iii) The lungs arc enlongate fu.,iform sacs of oranae
,colour lying on either side of the heart, dorsal to it, a~d
.extending posteriorly along the outer margins of the
liver lobes, extending upto two-ttlird of their lenO'ths.
(The posterior parts of the lungs in 'lome geckos'" are
'produced into narrow diverticula).
(iv) The liver is a bi-Iobed structure of dark-red colour
having a more or less, rounded gall bladder on Its right
lobe, towards its lower margin.
f;2
THE I .. IZARD
(v) The stomach is elongate tubular st.ructuH', the
anterior portion of which is covered over by t.he liver
lobes and lungs. It is attached to the body wall by a
fold of' peritoneum, the mesogaster.
(vi) The duodenum is the first part of the intestine
that forms a fold with the stomad}.
(vii) The pancreas is a diffuse gland lying in the fold
of the stomach and duodenum.
Disentangle the mtestilles,
spread them and measure
t],Cl1,1'I
(viii) The intestine is a coiled continuation of the duodenum attached to the body wall by a fold of peritoneum,.
the mesentery.
(ix) The rectum is the last portion of th~ 'tIimentary
canal opf:'ning into the cloacal chamber. It i." wider and
short tube. At it,s antf'rior end, or sometimes at the
junction of the intestine and the rectum, there is a short
coecum. It is attached to the body "all by a fold of
peritoneum, the masorectum. (In some of the ordinary
wall lizards coecum is quite small ancl in others absent.)
(x) The cloacal chamber is an elongate tubula"
chamber divided into an anterior and a posterior part.
Into the anterior part tIle rectum opens anteriorly.
a tbm walled urinary bladder ventrally and the genik. I
ducts open into the posterior part of the cloaca from the
dorsal side.
(xi) The kidneys are two dark.red bodies, e[.ell>
consisting of two lobes lying in the posterior part of the
body cavity, dorsal to the cloacal chamber, and conr,:,dI
by peritoneum only ventrally. Thl:'ir tapering posteriOD"
dortions lie almost in contact with one another.
THE LIZARD
53
(In the gecko the posterior portion of the kidneys
extend into the caudal region. The pelvic girdle has to
be cut in the middle to expose them fully. Their colour
is pinkish and not dark-red).
(xii) The gonads are not situated besides the kidney
.as in other animals. In the males the testes are oval
white bodies placed much anterior to the kidney. They
are not at the same level on both sides. In the female the
ovaries are irregularly oval bodies situated slightly
,behind the position taken by the testes in the male. In
the female two oviducts may also be found, one on either
side.
Draw a neat diagram showing the organs of the body
-cavity.
3. DISSECTION OF THE DIGESTIVE SYSTEM.
A.
The Buccal Cavity.
OPen the mouth cav~ty as fully as possible and study
the following salient feat1,tres.
(i) The teeth are conical and similar found on both
the jaws, The teeth ar13 fused directly with the
jaw bones. A patch of teeth is also found on
the roof of the mouth cavity, the palatine teeth.
(ii) The tongue is long, narrow' structure forked at
tho tip. It is attached to tho floor of the
mouth. At the point of its attachment it is
provided with a sheath into which it can be
retracted.
(In the geckos it is short and bifid posteriorly
drawn out mto pcocesses 0.:1 either side of the
glottis).
THE
LIZARD
LocatE' the glottis, gullet and the openings of theeustachian tubes.
Note.-Salivary glands are absent. Labial glands are'
pr('sent. The poison glands of the snakes are upper labiltl'
glands.
B.
The Alimentary Canal .
. (i) The pharynx is that part of the alimentary
canal where the respiratory and digestivepassap:es cross one another.
(ii) The oesophagus is a short muscular tube lying
dorsal to the ,vind pipe and connecting the
gullet with the stomach.
(iii) 1'he stomach is wider than thf' oesophagus
and has thick muscular walls. ~ nternnJly thestomach is lined by glandular tissues.
Cut open the stomach, wash its contents ani examine.
(iv) The duodenum has been described already.
Note its shape locate the pancreatic duct and
see where it opens in the duodenum.
tv) The intestine is re1atively short and a<; mu~J
is an organ of dIgestion
(also see page 52).
and
a&similation
(vi) The rectum or large intestine is also short and
opens into cloacal chamber.
C.
The Glands
Associat~d
with Dige'3tion.
(i) The liver has already been descr bed on page
51.
(ii) The pancreas is a diffuse gland producing thepancreatic juice and transferring the same to·
THE LIZARD
55
the duodenum through the pancreatic ducts
(also see page 52).
Sketch the organs of digestion.
4.
THE DISSECTION OF THE RESPIRATOB,Y
ORGANS
(i) The glottis is a slit-like aperture situated behind
t,he tongue.
(ii) The larynx is a short chamber into which the
glottis opens. Its walls are supported by the
cricoid (cricothyroid) and arytenoid cartilages.
(In geckos vocal cords are also present).
(iii' The trachea is an elongated cylindrical structure arising from the larynx. The walls of the
tube ~re supported by complete tracheal rings.
Posteriorly the trachea bifurcates into two short
bronchi each entering the lung of its side.
(iv) The lungs, as described earlier, are tubular
structures.
Cut open one of the l1tngs and examine its internal
make-up.
The inner lining of the lung is thrown into a network
(9f delicate ridges. It thus presents the appearance of a
honey-comb.
5. DISSECTION OF THE CIRCULAR ATORY
SYSTEM
A.
The Heart.
Remove the pericardium covering the heart, and careftilly
clean the base of the heart and roots of important vessels.
avoiding injury to them.
THE LIZARD
The heart is a triangular organ consisting of a sinus
venosus on the dorsal side, two auricles anteriorly and
a ventricle on the posterior side.
B.
The Dissection of the Heart.
Important.-The dzssectwn of the heart shottld always
be attempted after· completing the dissection of the blood
vessels. Remove the heart along with small lengths of the
important blood vessels, and examine.
(i) The sinus venosus is a triangular thin-walled
chamber on the dorsal side of the heart. At the two
anterior ends of the sinus the precavals enter. Posterior
apex of the sinus receives the large postcaval vein.
Cut open the sinus venoS2ts dorsally by a VeHtCaZ incision
and note:
(a) The sinu-auricular opening is oval and
opens into the right auricle.
(b) The sinu-auricular valve is a two lipped
valve guarding the opening. Do yV1t know
the functwn of such a valve?
(ii) The auricles are two-right and left-thin-walled
chambers externally separated by a faint groove. Externally the auricles are separated from the ventricle also
by a coronary sulcus.
Rcmove the ventral wall of the auricles carefully.
This reveals that internally the two aurides ale separated
into two chambers by a complete interauricu ~ar septum.
The interauricular septum reaches the auriculo-ventricular ap'erture dividing it into right and left, divisions'
This opening is guarded by the aurlculo-ventricular
THE LIZARD
57
'valve, attached to the posterior free end of the inter.auricular septum, and consisting of two semilunar flaps,
Dne guarding the right opening and the other the left.
Note the nature of the auricular walls.
(iii) The ventricle is a conical muscular portion of the
.'heart posterior to the auricles.
Cut open the ventricle and note the spongy nature of
its wall. The cavity is broken up by muscular trabeculae
with a relatively small central space.
The dorsal and ventral wall of the auriculo-ventricular
valves are attached by muscular bands to the dorsal and
ventral walls of the ventricle, thus, forming an incomplete
.septum dividing the ventricle into two chambers right
.and left. Of these the larger right IS the cavum venosum
whereas, the left one is the cavum arteriosum.
Trace the origin of blood vessels from these cavities.
,
{i) The pulmonary arteries arise from the
right of the partition.
(ii) The aortic arches arise from the left of the
partition.
Draw a neat figure showing the various parts of the
'heart. Draw separate figures of the dissection.
C.
The Veins.
WIth the exception of the blood coming from the
lungs, all the blood is retuI;Ilpd to thp heart through the
three large vpnous trunks which enter the sinus velJ-osus.
58
THE LIZA.RD
Impc;>rtant.-Tho veil1'l are relatively
therefore, they should be dissected first.
superfeciaf,.
Immedwtely on re11lIJv11lg the pericardi1t1n, clean the
roots of vartous blood vessels, and push the heart towards
one side. This wtll expose the precaval. H avzng loc~ted it
trace the branches opening mto it and dissect them to the
places where from they collect blood.
(i) The right precaval receives blood through three
prominent veins the internal jugUlar. the external
jugular, and the subclavian. The subclavian receives
the blood from the region of the fore limb and pectoraf
girdles etc, the internal jugular from the brain etc.,
where as, the external jugular passes forward by the side
of the trachea and receives blood from the tongt'e etc.
(ii) The left precaval receives blood onh from theinternal jugular and the subclavian. The external'
jug"!llar is absent in this case.
(I n the gecko we found the external jugular veins'
on both the sides running on either side of the trachea
and posteriorly opening in the precavals of both the sides.)
.
Remove the peritonelt1n covering the posterior vena cava.
Pttsh the 1'iscera towards one side. Be carefttl not to break
tfte hepatic portal and the anterior abdominal ~'eills while
doing so.
(iii) The posterior vena cava. The renal yeins
collecting blood from the substancp- of the kidneys uniteto form a pair of large trunks, each running along the
inner border of kIdneys. Both these unite a little distance
ahead of the kidneys to form the median postcav.1l, which·
runs forwards and opens into the sinus venosus.
The two efferent renals forming the postcaval anteriorly
are continued behind the posterior t'dge of the kidneys and
THE LIZARD
59
meet in the median line forming a sort of loop. The
postcaval receives two hepatic veins from the liver
before entering the sinus.
(iv) The Portal Systems.
a.
The Hepatic Porta] System.
5 pread the fold of mesentery supporting the duodenum
and the stomach as fully as possible, without injuring the
delicate vessels.
The main trunk of this system takes its oflgm·
posteriorly from two very prominent veins lying one on·
each ,side of the rectum. These two originate directly
from the posterior end of the renal portal vein.
A number of small veins, such as the gastric,.
pancreatic, splenic and mesenteric collect blood
from thE' various parts of the alimentary canal and open
lnto the main trunk to form a prominent vein, thehepatic portal vein which opens into the liver.
(In the uromastix and geckos the hepatic portal
is formed only by the union of a number of blood vessels·
from the various parts of the alimentary canals.)
Do you know what is a portal system ?
b.
The Renal Portal System.
Expose the caudal vein and trace its bifurcation jast at
the base of the tail. Dissect out the femoral and sciatic veins.
from the leg and trace thezr connectio1ls with the pelvic.
5 pecial care is needed to keep the anterior abd'lminal intact
THE LIZARD
(i) The caudal vein collects blood from the
tail and bifurcates into two renal portal
veins immediately on emerging from the
tail region.
(ii) Each renal portal vein continues forward
into the kidneys. Close behind thf' kidney
the veins from the hind legs, the femoral
and the sciatic, join the rf'nal portal. Still
further backwards arises the root of the
hepatic portal vein.
{iii) The anterior abdominal vein is formed
by the union of the two pelvics. After that
it bends upwards then forwards, runs over the
viscera and opens into the left Jj'Ter lobe.
The pelvics do not arise directly from the
caudal 01' the renal portal vein, but ar,' formed
by a number of small vessels from tlwir side.
They do have indirect connections with the
renal portal.
(In geckos and the uromastix the pelvics
directly arise from the C'1udal and they
receive the femoral and the sciatic veins
from the leg before curving upwards to form
the anterior abdominal .vein.)
Make a neat diagram of the venous system.
D.
The Arteries.
Both the right and left systemic aortic arches persist
in the lizards, but the important one is the right arch as
it gives rise to ~he carotid and subclvaian arteri ~S.
Locate the arches and trace them forwards. Some of the
veins may prove bothersome. They can be safely removed to
expose the artenes as they h:we bem examined ani sketched.
THE LIZARD
Gf
.(i) Tho right systemic arch arises along with the
left systemic arch from the left. part of the ventricle.
(:1) The carotid arterips arise from the right
aorta and each runs parallel with the
corresponding aort,ic arch for a little distance,
tllen curves forwards and runs along the
sIde of the trachea. Before entering the
head It divides into the internal and
external carotids.
lIn geckos and other lIzards the carotid is connectl:!d with the systemic behind by means
of ducts caroticus tHst where it turns
towards the anterIOr side).
(b) The subclavian
artpries arise from the
right aortIC arch hefore it meets the left
arch. Both the fIght and left subclavian
take opposite courses and supply respective
fore-limbs.
(ii)
The left systemic arch does not giverise to corresponding blood-vessels.
(iii) The Dorsal Aorta.
Both the aortic arches curve backwards around the
oesophagus then run dorsally and meet each other in the
middle forming a median blood vessel, the dorsal aorta.
The dorsal aorta runs straight behind giving a number
of branches, and goes up to the tail rpgion where it is
known as the caudal artery. Other brll,llches of thedorsal aorta are as foll\nvs:
(a) The coeliaco-mesenteric is the first
median artery arising from the aorta just
after it~ formation. It divides into an
62
THE LIZARD
anterior branch or the coeliac artery and a
posterior branch, the anterior-mesenteric. The coeliac supplies, by means of
narrow branches, the stomach, the pa,ncreas
and the liver. The anterIOr mesenteric
supplies the intestine, spleen and cloaca etc.
(b) The posterior mesenteric is the second
median artery arising from the dorsal
aorta a little distanC'e behind the origin
of the coeliaco-mesenteric. It supplies the
large intestme.
genital arteries are a pair of blood
vessel'! arising from the aorta and supplying the genital organs. In the mal.~s they are
called the spermatic arteries tmd in the
female the ovarian arteries.
(e) The
The renal branches arise from the aorta
as a pail' of delicate vessels just before the
aorta enters the region of the kidneys and
supply the kidneys.
(e) The iliac arteries are two arising from the
aorta in the pelvic region and supplying
hind-limbs. Each iliac subdivides into a
femoral artery and another sciatic artery
supplying the outer and inner margins of the
leg.
(f) The intercostal branches are 11, series of
pairs of delicatf' vessels arisinf from the
aorta that supply the intercostal muscles
in the region of the ribs.
Sketch the arterial system.
THE LIZARD
6.
THE RENAL AND REPRODUOTIVE SYSTEMS.
A.
The Urinary System.
Remove the peritoneum covering the kidneys and cut the
pefvic g~rdle in the middle to expose the kidneys Jully.
(i) The kidneys a,re two dark-red bodies situated
in close contact with the dorsal wall of the
posterior portion of the body cavity. Each
is roughly divided ink) two lobes. Their
posterior tapering portion is almost in contact with each other.
(ii) The ureters are delicate ducts arising from
the kidneys and opening posteriorly in the
cloaca.
(iii) The urinary bladder is a median thin_walled sac opening into the oloara ventrally.
_E.
The Reproductive System.
(a) The Male.
(i) The testes are two oval white bodies situated
in the body cavity quite' ahead of the kidneys. Note that both the testes are not on
the same level. The right testis is anterior,
situated just behind the right lobe of the
liver; whereas, the left testis IS situatei
posterior to this on the left side.
,(ii) The mesorchium is the fold of peritoneum
that k3eps each testis attached to the body
wall.
-(iii) The epididymis is on the inner side of
ea ch testis and is formed of a convoluted
mass of narrow tube'_ Each continues
64
THE
LIZARD
behind as a narrow convoluted tube, thevas deferens which runs posteriorly and
joins the ureter of its side before openinginto the cloacal chamber. Thus, the ureter
and vas deferens open by a common'
aperture.
(iv) The copulatory sacs are two eversible
hollow sacs opening into the posterior wall
of ,the cloaca. They are made l1p of erectile'
tissue when everted they become cylindrical. A groove runs to them from the
opening of the vas deferens for the conveyance of the spcrm.
(v) The Cloaca.
,Cut open the wall oj the cloaca Jrom one sid!' and turn
the ventral wall towards the other slde.
Internally the cloaca is divided into two chambers by
a ridge of the dorsal waH. The ractum and the urinary
bladder open into the anterior division of thl) cloaca,
whereas, in the posterior division are the openings of the
urino-genital ducts. The copulatory sacs ca.n also be
seen a330ciated wit~ the posterior wall of the cloaca.
(b) The Female.
(i) The ovaries are irregular shaped organs.
situated in the posterior part of t e body
ca.vityanterior to the kidneys (not as much.
as the testes'. Their upper snrface seems
studded with rounded protuberances representing the ova.
(ii) The mesovarium is a fold of peritonenm
that keeps the ovaries attachedl to the dorsalt
wall of the coelom.
65
THE LIZARD
(iii) The oviducts are two thin-walled tubes
whose walls are mnch folded internally.
Anteriorly the tube is wider, much 'plaited
and opens by a longitudinal opening facing
sideways. They run posteriorly and open,
independent of the opening of the ureters,
into the posterior division of the cloaca.
(iv) The broad ligament is a fold of peritoneum
that keeps the oviduct of each side attached
to the body-wall.
$
(v) The cloacal chamber is similar to that of
the male but for the fact that the openings
of the urinary and genital ducts are sepa.
rate, and that the copulatory sacs are not
developed at all (as in .gecko) or are rudimentary.
Draw sketches of the male and the female generative
organs separa.tely.
7.
THE SKELETAL SYSTEM.
Preparation of the Skeleton.
Thc most prevall:'nt method of preparing a skeleton is
by boiling, but the method has it,s disadvantages. Boil.
ing separates most of the small bones particularly those
of the carpus, digits etc., and oftl'n bones of the skull,
and besides by this method the skeleton is not
perfectly white. The best method to be recommended for
student work is by maceration.
Take a fairly large-sized animal, after skinning cut 0 if
the flesh covering the bones. This should be done very carefully in thf; region of tlte ribs, sternum, hand and foot. After
cleaning as much as possible transfer it to a small trough
containing lime water and leave it overnight. Take it out
5
66
THE LIZARD
next morning, dry the bones with a duster and scrape off the
bones slowly and carejully remove all the traces oj mzescles
and tiss~tes. Again steep them in lime water, overnight, to
sojten the tisszees, and clean the bones as much as possible
next morning. For this and jurther cleaning it is better to
1tSe an old tooth brush. Repeat the process till the bones
are completely cleaned and jree oj the offensive smell. For
final dipping a clear solution of bleaching powder can be
1tsed. Bleaching in this case is done by dryi1'g the thus
cleaned skeleton in the sun, for a lIulnber of days.
This is definitely a long process but a better one.
A. The Axial Skeleton.
The vertebral column consists of a large number
of vertebrae usually divided into cervical. thoracic
(thoraco-lumbar), sacral and caudal regions.
(a) The Cervical Region.
(i) A typical cervical consists of a stout cen·
trum which is hollow in front and convex:
behind i.e. procoelous. The neural arch
bears a prominent crest·like neural spine.
Anteriorly it bears articular facets, the prezygapophyses that are directed upwards,
and posteriorly other set of articular facets,
the post zygapopbyses, that are directed
downwards. Posteriorly the centrum bears
a backwardly directed process, the hypapophysis on the ventral surface. All the vertebrae behmd the tbird have aJt;l!ular sur·
faces for the cervical ribs.
(ii) The atlas or the first cervical is ring-like
having no distinct centrum. Tnfact the ring
is made up of three bony pieces, one ventral
occupying the place of the centrum and two
THE
67
LIZARD
dorso-lateral arching over the Yl'ntral. The
latter two do not meet in middle though
they appear so, as the space in between
them is filled by membrane. A transverse
ligamentous band is seen dividing the ring of
the atlas int) two. Ventrally on its anterior
face is found an articular facet for the occipital condyle.
c
D
Fig. 5.-A, anterior view of atlas; B, lateral view of
axis; C, lateral view of 3 typicnl cerviraJ.;
and D, posterior view of a caudal vertebrae
of the varanus.
(iii) The axis or the second cervical vertebra
is just like a typical cervical il} structure,
but it is slightly larger and bears a hook
like l)rooe88, the odontoid process, on the
ventral surface of the centrum towards the
anterior end. The pointed ~ip of the process
is directpd inwards towards the hypapophysis). The neural spine is a large plate like
structure. The pre-zygapophyses are represented by mere notches, whereas, the
Ipost..zygapophy8es are as usual.
68
THE
LIl~ARD
(b) The thoraco·lumbar vertebrae are like thetyPical cervical, as described above, but for the fact
that they are somewhat larger and that each bears prominent articular facets, the capitular facets, at the
junction of tne centrum and the neUTaf arch, for the
articulation of the ribs. ThE' first few thoraco.lumbar
vertE'brae also bear hypapophysE's ventrally which go on
dwindling in size, and finally disappear.
(C) The sacral vertebrae are two in number and
articulate with the ilia of the pelvic girdle. They are,
therefore, very stont. The c{'ntrum in each case is stout
and short and 'bears strong expanded transverse proces·
ses The tips of the transverse processes of the anterior
vertebra are deeply notched to provide articulation space
for the ilia.
•
Fig. 6.-Lateral view of the sacral vertebraE' of the
varanus.
Note the nature of zygapophysE's.
(d) The caudal vertebrae are numerous and becomegradualy smaller towards the posterior side. so much so,
that at the end of the .tail the whole vertebra is just a
bony red. The anterior caudal vertebrae hav(· relatively
longer centra, slender transverse processes and longerneural spines. These vertebrae have Y shaped chevron
bones attached to the ventral' Burfaces of the centra. Twoupper limbs of Y articulate' with the' centrum, thu8 r
enclosing the haemal canal ..
THE LIZARD
{.e) The Ribs and Sternum.
(i) The ribs are slender curved rods.
They are
singlA headed and are attached to '-the
vertebrae between the centrum and the
neurqI arch.
Excepting the firilt three
vertebrae, all preeaudal vertebrae bear ribs.
The cervical ribs are short rods not conneded with the sternum.
The thoracic ribs are relatively larger
and are connected with the sternum by
cartilaginous sternal ribs in the first three
thoracic vertebrae. The fourth carries a
little cartilaginous rod attached to its free
-end representing the dwindling sternal rib.
In other vertebrae the ribs are short and
free ventrally (not connected with the
sternum).
{ii) The sternum consists of a rhomboidal plate
of cartilage from the
posterior end of whicl).
articulate two sternal
ribs. From its posterolateral edges articulate
two sternal ribs on each
side .
•
Anteriorly the apex i'l
drawn out into a long
narrow rod of cartilage,
the
inter-clavicle
which ends forming a Tshaped structure. Tho:
vertical limb of T continues on the ventral
Fig. 7.-The sternum of the
varanus. 4)
70
THE LIZARD
surface of the sternum; on the small
anterior arms of Trest two clavicles of eithersides.
The bones of the pectoral girdle articulate with thenutero-Iateral borders of the rhomboidal plate.
B.
The 81\:ul1.
The skeleton of the head, like that of the dog-fish, consists of the cranium proper, the olfactory and auditory
capsules, and the visceral skeleton, but the viscl:'ral skeleton, including jaws, hyoid bone and auditory ossicles is
so closely associated with other parts that it is convenient
to describe all these parts under 'skull'.
(1) The cranium proper forill8 the posterior part of
the skull that lodges the brain. [n the varanll::l, as in
othE'l" lizards, some important bones of the craniuUl, such
as the Itlisphenoids, orbitosphenoids and the pl'esphenoids,
are missing. In th.;;) birds and mammals these bones form
a. major part of the cranium ventrally. ThitJ part of the
brain box is formed by membrane8 in the varanus.
Pick up the skull in your left hand. Examine the bOlles
of the branl-case starting from the posterior side.
(a) 'rhe occipital se~ment forms thp po;;tel'iormost part of tIl(> brain ('USl around the
foramen magnum. It ('ollsists of foUl'
boneR which fuse inseparabI~'. Of theRe
the baSi-occipital fOfIllti the base, the
exoccipital the sides and the supra-ocdpital
forms t,h(> roof. ThE' ba~i-o('('ipital carrieR
the occipital condyle mainly fornwd by it.
(b) The parietal
segment ('olltihts of: (i) a
broad basisphenoid with two prominent
71
THE LIZARD
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72
THE LIZARD
processes at its antero-Iateral sides, forming
the base, and; (ii) the parietals forming
the roof. The two parietals are fuscd
completely in the adult even a suture is not
visible. The parietals are narrow posteriorly
and broad anteriorly. A pineal foramen
is found on the parietal bituated a little
interior to the sut,ure of the parietal with
the frontals on the mid-dorsal line.
The sides of the parietal segment are not
covered by bones, as in higher fl.nimals,
because the alisphenoids are ab!:!ent and the
membranous tissue that takes their place
is removed while cleaning the skull.
Nete: A careful examination reveals that tIle parietals
are not joined with the supra-occipital by "uture but
there is a distinct gap which is filled up by fibrous tissue
that is removed during cleaning. The fronto-parietal part
of the skull that can be seen separate is slightly moveable
upon the occipita-sphenoidal part.
se~ment is incomplete. It is
without a base as the presphenoid is absent,
and without sides even, as the orbitosphenoids are absent. These are replaced by
membranous tissues. The roof, however,
is formed by the paired frontals that
are suturally fused in the middle line. Posteriorly the frontals are s6parated from the
parietals by a distinct suture, the coronal
suture.
(c) The frontal
(2) The olfactory capsule is dorsally covered by the
nasals and floored by the vomers. The nasals are flat
triangular bones fused in the middle. The rod-shaped
THE LIZARD
73
vomers are two separated posteriorly but fused with each
other anteriorly. They form the inner margin of the
posterior nares.
(3) The auditory capsule usually consists of the
opisthotic, epiotic and pro-otic, of which, in this
animal, the epiotlc is fused with the supra-occipital the
opisthotic is fused with the ex-occipitals, only pro-otic
remains separate.
(4) The suspensorium.
(i) The parotic process is formed by the prolongation of the exoccipitals and pro-otic.
Each is a horizontal process directed outwards and slightly backwards, on either
side of th\' foramen magnum, and articula.tes with the squamosal and the quadrate.
\(ii) The squamosal is a short bony rod bending
forwards and upwards, attached to the
parotic process posteriorly.
Anteriorly it
extends forwards to the post-frontal (except
in geckos) forming the supra-temporal
arcade.
(iii) The quadrate is rod-like bone attached
to the anterior aspect of the parotic process
directed forwards and downwards articulating with the pterygoid.
(5) The temporal region.
(i) The posterior temporal fossa is a vacuity
guardI'Jd ventrally by the parotic and dorsally by paricto-squamosal or posterior tempora! arcade. The parietal sends out a
proctlss posteriorly which fuses with t he
squamosal forming the parieto-squamosal.
74
THE LIZARD
(ii) The supra-temporal fossa is the cavity
between the supra-temporal arcade (formed
by the union of the sq uamosal and the
post-frontal) and the parietals.
(iii) The lateral temporal fossa is bridged over
by the supra-temporal and its posterior"
margin is formed by the quadrate. Ventrally
it is open as the quadrato-jugal is absent.
and no infra-temporal arcade is formed, and
anteriorly, also, the fossa is hot closed as
the jugal is not joined with the post-frontal.
Thus, the orbit and the fossa communicate.
(6) The orbits are large and closely approximatedl
being separated by only a thin vertical interorbital
septum. Dorsally it is roofed over by the fronl.als and'
anteriorly it is bound by a small bone pre-fJ"orl.tal and
another perforated bone, the lacrymal. Posteriorly
the orbit is incompletely bound by the post-frontall
(dorsally) and jugal (from ventral sidl'). Another triangular bone, supra orbital over-hangs thl' orbit. Its flat
base is attached to the anterior angle of the orbit formed'
by the pre-frolltals and the lacrymal, while the pointed
free end is directed towards the post-frontal.
(7) The bones of the maxillo-palatine appamtus
(i) The premaxillae are fused in the middle-"
forming the antenor extremity of the snout.
The median bone, thus formed, bears six to
eight small te('th.
(ii) Th(' septomaxillary is a small bone OIl!
each side just above the vomer in the
anterior part of the lGasul region.
(iii~
The maxillae are a pair of irregular bone~
forming a large part of the skeleton of the
75·
THE LIZARD
upper jaw. Its body is called alveolar'
portion as it bears teeth. The palatine
process is not well developed in this' case,
thus, leaving space between the maxilla
and palatine. The maxilla bpars conical
teeth ankylosed to the bone by their sides
just, inside the edgp.s of the jaw (pleurodont).
(iv) The palatines are irregular bones and pass.
backwards from the vomers and thfr
maxillaries to the pterygoids.
(t) The pterygoids are again irregular bones,
which, diverging from one another, extend
backward to tIle quadrate articulating in
the way with the lateral processes of the
basi-sphenoids.
Extending between the
pterygoids (below) and the parietal above
of each side there is a rod shaped bone called
the epipterygoid which is also called
'Columella cranii. (To avoid confusion with
the columella auris it is better to call it
epipterygoid).
(vi) The transpalatine is a small bone pllssing
from the pda.tine and pterygoid to meet at
the junction of maxilla and juga].
(8) The lower jaw consists of two rami each made up
of six bones the dentary, angular, supra~angular, artiCORONOID
0'":""' A.::;HNr.UL••
~"~b
,.
...
ANGULAR
AP.TICUL.A~
SPLf.NIAL
Fig. 9--0ne ramus of the lower jaw of the Varanus.
THE LIZARD
...
eular, coronoid and the splenial. Of these the dentary
is the largest, constitutlllg almost the anterior half of one of
the rami of the lower jaw bea~; the pleurodont teeth.
The posterior half of the ramus consists of a triangular
,coronoid with a backwardly direeted process, at the top;
the supra-angular, a flat elongated bone in the middle,
.and the articular and angular below; the angular is a.
small bone wedged in betweep. the articular and dentary.
The s'plenial is found lodged in a groove on the inner face
of the dentary, from outside only a narrow slip is seen
below the dentary.
(9) The hyoid apparatus consigts of an elongated body
or the basihyal and two long cornua on each side. The-",
anterior cornua are elongated cartilaginous rods that
curve inwards and flatten at their free ends. The posterior cornua are cartilaginous rodB arising from the posterior end of the basihyal, each consisting of two '''ieces.
B. The Apendicular Skeleton.
a. The pectoral girdle consists of two similar halve~
<lying one on either side of the inter-clavicle. Each half
{:onsists of a supra-scapula, scapula and coracoid.
(i) The supra-scapula is a flat distally expanded plato made of cartilage articulating
internally with the scapula.
(ii) Th.e scapula is oblong bone constricted in
the middle. Its end articulating with the
supra-scapula is broader The posterior side
of the lower end forms part of the glenoid
fossa.
From the anterior side of the
scapula, just opposite to the glenoid cavity
arises a completely ossified prO( ess, the
mesoscapula.
,(iii) The coracoid is a stout bone constricted in
the middle and broadly expa.nded at its
THE LIZARD
77
inner end. At its out,er extremity the cora-coid also bears a flat process, the meso-coracoid.
(iv) The epicoracoid, an irregular
shaped
cartilage starting from the proxi~al end of
the coracoid, runs along the inter-clavicleupto its end, whence it bends back and,
runs to the mesoscapula. Before turning
back it also gives a process to the mesoco-racoid. Thus, the whole of the epicoracoid
appears fenestrated.
b.
The Fore Limbs.
(i) The arm consists of the humerus both theends of which are greatly expanded. Thehead lies at the proximal end and the distal
end has pulley like articular surface, the
trochlea that articulates with the radiuS'
and ulna. A prominent crest like deltoid,
ridge L"I also present.
(li) The fore-arm
consists of two bones of'
which the radius is slender consisting of"
a shaft and two epiphyses. Distally it has
a concave articular facet for the carpus.
The proximal end of the ulna is produced
into a. upwardly directed olecranon process,
while the distal end bears a convex articular
surface for the carpus.
(iii) The carpus consists of ten polyhedral carpal
bones arranged in three rows. 'The proximal
row consisting of three, (the radiale, ulnare, and intermedium), the central row
6f one (centrale) and the distal row of five-
THE LIZARD
smail pieces. Besides these, the pisiform
is attached to the distal epiphysis of the
ulna on Its post-axial side.
(iv) .The di~its are five each consisting of a
metacarpal bone a,nd varying number of
phalanges. The first digit (pollex) has two
phalanges, the second three, thfl third four,
the fourth five, and the fifth hl1.s three
only.
c. The pelvic girdle consist,s of the ilia, pubes a.nd
Ischia which form two triradiate bones, the ossa
Jnnominata.
(i) The ilium is a compres'led rod pl~ssing upwards and backwards to 9.rticdate with
the sacral vertebrae.
\ii) The pubis on each side
passes downwards
and forwards to meet its fellow in the middle
line at tho pubic symphysis. Between
the anterior ends, of the pubis, in front, is
a nodule of calcified cartilage, the epipubis.
On the other end, near its fusion with the
ilium and ischium each pubis has an oval
foramen for the obturator nerve. Just
external and slightly posterior to the foramen arises the pre-pubis which is a small
rod like process directed outward.
,(iii) The ischium runs inwards and meets its
fellow at the ischiatic symphysis. Hypo-ischium is a small piece of calcifi('d
cartilage in between the two ischia, at the
anterior face.
THE LIZA.RD
79
r(iv) The obtut'ator foramen
is (1 wide space
between the pubes and ischia. This is
divided into two by a median ligament.
The ligament is often removed while cleaning.
(v) The
acetabulum is a concave articular
surface for the hC'ad of the femur. It is
situated on the outer side at the point
where the three bones fuse. At the base
ot the depression the' lines of fUf'ion can be
seen ell-arly.
,d.
The Hind Limbs.
(i) The femur is a stout bone of the thigh. Its
anterior epiphysis develops a rounded head
that fits into the acetabulum. Neltr the
head rather a bit posteriorly on the preaxial side is the prominent lesser trochanter. The greater trochanter on the postaxial side is ncarly obsolete. The distal
extremity is pulley-shaped having two
condyles for the articulation of the tibia
and fibula.
,(ii) The shank or crus consists of tibia and a
fibula. The tibia is stout, bone bent
inwards (towards fibula), having a longitudinal ridge, the cnemial ridge along
the dorsal edge. The fibula is slender bone
the proximal end of which articulates with
the femur and the distal with the tarsus.
,!iii) The pes or tarsus consists of only five tarsal
bones in the adult. Two of the proximal
row are suturally fused and articulate with
the tibia and fibula. The distal row consists
so
THE LIZARD
of three cuboid bones of different sizes:
articulfl.ting with the metatarsals of thetoes. The number of phalanges in each
toe is variable; the first has two, the.second three, the third four, the fourth
five and the fifth three.
CHAPTER
~
1.
A.
IV
PIGEON
EXTERNAL CHARACTERS.
The Divisions of the body.
(i) 1'he head is elongated antero-posteriorly with it~
rounded cranium and prominent beak formed by the
upper and lower jaws covered by horny sheets. At
the base of the beak is a nakEd swollen patch of skin, the
cere.
, The eyes are large and provided with the upper and
lower eyelids and a semi-transparent nictitating membr:.:tne.
(ii) The neck is long cylindrical and very mobile
sharply marked out from the head and the trunk.
(iii) The trunk is plump and somewhat compressed
from side to side. The' boat-shaped carina or keel of the
sternum is raised into a prominent ridge along the midventral line. Posteriorly the trunk is drawn out into a
short conical projection, the true tail or uropygium,
from wliich originate a group of large feathers, to which
the term "tail" is generally applied.
B.
The Limbs.
(i) The wings show three typical divisions of
the fore-limbs, the upper arm, fore-arm and
81
6
82
THE PIGEON
the hand. The parts of the hand are closely
bound together by skin. The several bones
can be identified by feeling them through
the skin. Between the upper-arm and the
fore-arm, on the anterior side extends a
fold of skin the alar membrane or prepatagium. A similar fold exists between
the posterior portion of the upper-arm and
the trunk, this is the post-patagium.
fii) The hind limb has a short thigh closely
bound to the trunk, a long shank extending from the knee downwards and backwards and a foot clearly divisible into a
proximal portion, the tarso-metatarsus,
and four digits.
/
C.
The External Apertures.
(a) Median A PerillreS.
(i) The mouth is terminal guarded by the upper and
lower jaws covered by horny beak. It has a wide gape. _
(ii) The cloacal aperture is a large transverse slit
situated ventrally at the junction of the uropygium and
the trunk.
(b) Paired Apertures.
(i) The nostrils are a pair of slit-like apertures between the beak and the cere.
(ii) The external auditory apertures are two circular openings below and slightly behind the posterior or
outer angles of the eyes.
THE PIGEON
.v;;:
83
The Feathers.
Excepting the lower joints of the legs and the toes,
nearly the whole surface of the body is covered with
feathers, which are specially modified epidermal structures. (Compare with the scaly exoskeleton of fishes
and reptiles). To study ·the structure of a typical feather
get any, large feather and note the following parts.
'f. The Structure of a
Feather.
(i) The
calamus or quill is the hollow stalk
of the f{'ather having at its base a small
aperture, the inferior umbilicus. Into
this umbilicus fits a small conical prolongation of the skin, the feather papilla. A
second, extremely minute aperture is situated at the junction of the quill and the
vane on the ventral surface. This is the
superior umbilicus.
Important: In the pigeon, as in many other birds,
the superior umbilicus appears to be covered by
numerous hairy outgrowths, the aftershaft, which has to
Ibe scrapped off by a scalpel, to see the superior umbilicus
situated in a pit.
(ii) The rachis or shaft is the distal solid continuation of the quill tapering towards the
tip. It is often grooved along its ventral
side.
(iii) The vane
or vexillum is the expanded
portion of the feather developed around
the rachis as its longitudinal axis. The
vane is apparently like a continuous sheetlike structure formed by barbs and
.barbules.
84
THE PIGEON
Exami1tc the vane under a microscope or strong magniJying lens and note:
(a) The barbs are delice~te thread-like structures attached to each side of the rachis
and extend obliquely outwards.
(b) The barbules are extremely delicate oblique filaments attached to the sides of the
barb. They bear hooklets; which hold
the adjacent barbs together, and so give the
feather t,he power of resistance to the air
needed for flight.
II.
Kinds of Feather.
(a) The quill feather are the largest feathers
of the wings and tail. The wing -luills are
known a,';; remiges and the tail quills are
rectrices.
(i) The remiges have inner or posterior half
of the vane much broader than the outer
or anterior half.
(ii) The rectrices have the two sidei.'
vane almost equal in size.
of the
Count the number oj these and note.
(b) The coverts arc structurally similar to the
quill feather but smaller in size. They cover
the bases of the quill feathers of the tail
and the wings.
(c) The contours arc short, and wooly feathersforming a general covering of the body. Tn
THE PIGEON
85
these, the barbules are much less developed
and the barbs are loose and can be easily
separated.
(d) The filoplumes are delicate feathers having
a hair-like stalk with fine barbs at the top.
There is no interlocking arrangement of the
barbs. Tht'y are seen scattered on the
body surface after the bird has been plucked.
(e) The down feathers are soft, wooly and
transitory, found only in the newly hatched
bird. Each has a short stalk bearing barbs
at the tip but no interlocking arrangement
is present.
'2.
DIS~EOTION
OF THE MUSOLES OF FLIGHT.
Plnck the bird thoroughly particularly the ventral aspect
-of the thorax and wings. Lay it on tlte back on. the dissection
board and pin keeping at least one wing fully stretched.
Remove the skin from the ventral surface of the thorax and
from one shoulder and the wing.
The bird has one depressor, one elevator, two acce3sory
.depressors and four tensor muscles.
A.
The depressor and elevator muscles.
(i) The pectoralis is the large3t of all the
muscles, triangular in shape occupying the
whole space of the ventral half of the keel
of the sternum. Its broad flat tendon is
inserted into the deltoid ridge of the humerus.
It is the great depressor muscle i.e it pulls
the wing to thc lower side.
86
THE PIGEON
Cut inwards with a fine scalpel along the mid·ventrcrt
line. Go on cutting along the latero-ventral aspect of th'
keel to the anterwr side. As yDtt proceed towards the anterior
side, be careful to locate certain blood vessels that emerge
from the anterwr side of the keel and tztY1t backwards and
sideways to suPPly the pectoral muscles. Clean these blood'
vessels and ligature carefully. Tum the muscle tozwards the
anterior side keeping the tendon in its normal position.
(ii) The subclavius is a much smaller muscleand more deeply placed. It is similar in
shape to the first and completely covered
by it. It arises from the posterior part of
the side of the keel of the sternum, on its
ventral surface. Its long narrow tendon
passes through the foramen triosseuw. (openmg formed by three bones i.e. the scapula,
coracoid, and clavicle) and is inserf,.'d into
the dorsal surfacl' of the humerus, ncar thedeltoid ridg0.
It is the only muscle that elevates the wing,
hence, called elevator. Being attached just
ltke the pectoralis and being of the same shape
how 1S that it flt11ctlO'HS m entirely reverse
manner 1
Important: To see the insertion of tIle tendon of th('
subclavius, push aside the deltoid mUbele that covers t,lw
back of the shoulder-joint.
Remove the pin from the 'Irillg and pull the I1lZtscles Olle:
after another to test the actton of the J1ttlscles.
B.
The Accessory Depressors.
(i) The coraco-brachialis longus appears as
a triangular muscle immediately on clearing
the pectoralis and the subclavius. It arises
THE PIGEON
87
rom the posterior two· third portion of the
coracoid, and from the costal process of
the sternum. Its narrow tendon is inserted to
the post· axial aspect of the head of the
humerus.
(ii) The coraco-brachialis brevis is a narrower
muscle infront ot the coraco·brachialis
longus.
Cut the anterior one-third portion of the coracoid to
expose these muscles fully. .
It arises from the middle of the antero·
dorsal aspect of the sternum just in between
the junction of the two coracoids. The
COl aco· brachialis brevis muscles of both the
sides anse from the sallle place and take
opposite courses.
Note: In some pigeons, that are specially kept for
flight, we found two divisions of the muscle--one going to
the dorsal aspect, as described and the other turning round
the comer internal to the foramen triosseum to be
attached on the antprior aspect of the hUlllerus.
C.
The Tensor Muscles.
(i) The tensor longus is the longest among
all the tensor muscles. It arises from the
anterior side of carpometacarpus, runs along
the outer border of pre.patagium, and is
inserted to the front of the head of the
humerus. It is very delicate muscle in the
beginning and, thus, it often becomes difficult to distinguish.
(ii) The tensor brevis is a thin sheet of muscles
which spreads between the biceps muscles
88
THE PIGEON
and the posterior margin of the proximal
portion of the tensor longus.
(iii) The tensor accessorius is comparatively
broader muscle lying across the prepatagium. All these three muscles help to
keep the pre-patagium stretched while
flying.
(iv) 'rhe tensor posterious is a thin strip of
muscles that runs along the outer edge
of post-patagium and keeps it fully stretched during flight.
3. DISSECTION OF THE COELOM.
The Abdominal Viscera.
Lift Ztp the end of the sternum, and cut through its sides
about mid-way between the dorsal and ventral surface. Cut
through the coracoids about the middle of their length. Try
10 detach the sternum and note.
(i) The falciform ligamcmt will be visible as
soon as an attempt is made to lift t,he sternum. It is a median vertical sheet of peritoneum connecting the dorsal surface of the
sternum with the viscera.
(ii) The oblique septum is a fibrous membrane
attached to the pericardium infront and
separates the air-sacs from the general body
cavity. -'
After observing these, remove the sternum entirelY.
(iii) The heart is comparatively larger; it is
triangular in shape with the apex directed
backwards and is enclosed in the pericardium.
THE PIGEON
89
(iv) The lungs arc spongy bodies lying at the
sides of and dorsal to the heart and very
largely concealed by it. (They are not Sll.Clike as found in the amphibia and certain
reptiles.)
(v) The liver is a solid bilobed organ of darkred colour lying behind and at the sides
of the heart. The right lobe is bigger than
the left. Thorl? is no gall-bladder.
(vi) The great omentum is a fold of mesentery loaded with fat covering the viscera
behind the liver. It is continuous with
the falciform ligament infront.
Remove the great omentum and examine the organs lying
ilelow.
(vii) The gizzard is a large, hard, round body
lying behind the left lobe of the liver.
(viii) The duodenum is a loop of intestine
lying along the right side of the abdominal
cavity.
(ix) The intestiue forms a convoluted mass in
the hinder part of the abdomen .
.Push the intestine to one side and examine.
(x) The kidneys are dark-red fiat bodies, each
divided into three lobes, lying in the posterior portion of the body cavity on the
dorsal surface.
(xi) The spleen is a dark-red coloured elongated
body, of variable sizes lying dorsally to the
proventriculus.
90
THE PIGEOJ',[
(xii) The gonads, or organs of reproduction,
found associated with the kidneys, will be'
described later.
4-
THE DISSECTION OF THE DIGESTIVE
ORGANS.
A.
The Buccal Cavity.
OPen the mouth and cut about half an inch deep at the
angle of the jaws on both sides, turn away the jaws so as to
expose the buccal cavity fully.
~i)
The jaws are withoJ.1t. teet.h. The posterior naria! apertures are a pair of long
narrow apertures lying, side by side, in the
roof of the mouth. The anterior two· third
of their length are hidden by a pair of
prominent folds of the mucous membrane
of the mouth.
(ii) The apterture of the eustachian tube is
a median opening posterior to the nari,11
apertures
(iii) The tongue is marow and trianguhu' "ith
a sharply pointed tip. Posteriorly it is
produced into two lobes fringed with fine
horny processes.
(iv) The glottis is an oval aperture in t 1e floorof the mouth Just behind the tongue.
(v)
The gullet is a large wide opening behind
the glottis.
THE PIGEON
B.
91~
Tbe Alimentary Canal. .
Unravel the intestine by cutting through the mesentery-
close to it, but taking care not to touch tlte dztadenal loop.
(i\ The oesophagus- The gullet opens into a
long tube, the oesophagus, that runs back
through the nf'ck to the stomach. In the
neck region it enlarges to form a thin-walled
sac, the crop. It again becomes thickwalled as it enters the thorax.
(ii) The stomach or proventriculus is the
continuation of the oesophagus lying dorsally to the left liver lobe. It is comparatively wider and has thick glandular inner
lming that produces the gastric juice. To
its right side is attached the spleen.
(iii) The gizzard is a large hard body flattened
laterally forming a biconvex structure. Its
walls are thick and muscular and its inner
lining is horny. The cavity is very p,mall
and often contains small pieces of stones.
Why?
The oesophagus opens into the
gizzard dorsally, slightly to the left side,
while the duodenum leaves it a little tothe right side of the same spot.
e1ft open the gizzard along its
ventral edge and examine.
(iyJ The duodenum is a V-shaped loop formE'd
by the beginning of the intestine. Between
its two limbs lies the pancreas.
(v) The small intestine is a convoluted tube
of uniform diameter. It is the longest
part of the alimentary canal.
Exie1ld it ampletel)" 11'eaSZlre and nete tis length.
THE
PIGJiJON
(vi) The rectum is the terminal, portion of the
intestine. At its junction with the intestine
are situated two coeeal processes, the rectal
diverticula. The rectum opens in the
cloaca posteriorly.
{J.
The Gland Associated with the Digestive
System.
(i) The liver has been described earlier (page
89).
Of t4e two bile ducts, the left opens into
the proximal limb of the duodenum and
the right opens into the distal limb .
"\
The pancreas is It compact pinkish gland
(II,
lying in the loop of the duodemlm. It:>
three ducts, the pancrel}tic ducts, 0pen into
the distal limb of the duodenum.
Pin out the dttodenum on a dissecting bourd, and expose
the bile and pancreatic ducts. For better results do it
ttnder water.
5. THE DISSECTION OF THE CIRCULATORY
SYSTEM.
A. The Heart.
The large heart of the bird is four chambered-the
aerated blood is completely separated from the nonaerated. The dissection of the heart will be deferred to
a later stage.
The course of the blood shows that there is complete
.double circulation. The blood from the entin' 1)odv comes
to the right side of the ht'art, and thence driw to the
lungs to be aerated; lungs send blood to the left side of
the heart which derives it to all parts of the body.
n
OPen the pericardial cavity and expose tlte heart completely.
THE PIGEON
VEINS
ARTERIES
JUGULA R----- --
INTERNAlILlA(_(OCCYGto-
MESENTERIC _______ ~~~:...._
CAUDAL~----- ____ ~ -- _- - - - CAUDAL
Fig. JO.-Thc circulatory systt'm of the pigeon.
B. _The v:.~il1s.
As the veins lie, marc or less, superficially it is convenient to study them first. Veins are also thin-walled as such,
great care sholllcl be taken in clearing them.
'94
THE PIGEON
I. The venae cavae are three, all of which open into
-the right auricle, where they bring all the venous blood
.of the body.
(a) The right anterior vena cava is a small
thin-walled vessel that collects blood from
the right side of the head, the neck, the
right wing and the right side of the breast
through:
,(i) The right jugular vein that runs a.long the
right side of the neck, close to the vertebral
column and alm08t behind the oesophagus,
On the under surface of the base of the skull,
it un\tes with its fellow of the left side
forming a loop. During its course it receives veins from the sides of the neck,
the crop and the vert~bral colnmn of the
region by the oesophageal and tl.c vertebral
veins.
(ii) The right brachial vein returns blood from
the right wing.
-(iii) The right pectoral vein returns blood from
the large pectoral muscle. It also receives
a delicate internal mammary vein, that
runs along the inner surface of th~ thoracic
wall, before entering the precavaL
. (b) The left anterior vena cava is a corresponding vein of the left side receiving blood
through the blood vessels corresponding
to those of the right side.
,(c) The posterior vena cava is formed by the
union of the two iliac veins a little behind
the liver. In the region of the liver it
receiv{'s the hepatic veins.
'IRE PIGEON
95
To expose this blood vessel the heart has to be tltmed
;upwards.
II.
The V ei~s of the Posterior Part.
(i) The caudal vein is 11 small narrow blood
vessel collecting blood from the tail region.
(ii) The hypogastric veins are formed by the
bifurcation of the caudal vein. Each passes
onwards over the lddneys, sending off a
few brunches to the kidneys (carrying blood
to that organ), 8nd receiving a delicate
sciatic vein between the second and third
lobes of the kidney, n,nd a prominent,
femoral vein, returning blood from the
leg, between the first and sec-ond lobes of
the kidney.
,(iii) The iliac vein, formed by the union of the
femoral and the hypogastric, leaves the
kidney at its inner border. between its
anterior and middle lobes, and then runs
forwards, joins its fellow of the other side
and forms the posterior vena cava.
~iv)
The internal iliac veins are a pair of small
vessels, each joining the hypogastric coming
from the inner surface of the pelvic cavity.
(v) The coccygeo-mesenteric vein arises from
the caudal vein before it bifurcates into the
hypogastrics.
1t run\) parallel to the
rectum and intestine, to a little distance
and opens into the hepatic portal.
{vi) The posterior mesenteric vein returns
blood from the hinder part of the body
96
THE PIGEON
cavity and mesentery etc. into the coccygeomesenteric just near its root.
(vii) The hepatic portal vein.
Spread the fold of mesentery, the great omentum, supporting the hinder part of the mtestine carefully and note
the fine blood vessels.
The hepatic porta.l vein is formed by a number of
narrow blood vessels coming from tlle various organs
of the digestive system On reaching the liver it bifurcates into two branches, one going to eaClh lobe. The blood.
from the greater part of the alimentary canal is conveyed
to the liver whence it goes to the heart.
Ill.
Veins
openin~
into the left auricle.
The pulmonary veins are the only two very ",hort blood.
vessels that bring blood back from the lungs and open
into the posterior surface of the left auricle. What type
of blood tS returned by these?
C.
The Arteries.
I. The rigbt aortic arch is the only arch
arising from the .left ventricle. It curves·
over the right, branches and passes backwards as the dorsal aorta. Immediately
after origin it gives rise to two, right and
left, innominate arteries which appear
more prominent than the aorta itself.
(a) The left innominate artery is a prominent,
though short, art!:'!'? and during its course
it gives ['iee to the following branches.
(i) The left carotid al'trry arises after about a
quarter of an inch of its course. It runs-
97
THE PIGEON
anteriorly bending towards the mid-ventral
side and finally it enters a groove on the
ventral side of the vertebral column of the
neck. In the same groove, lies, close to its
side, tl:c carotid of the right side.
About an inch after its origin below the
thyroid gland it gives rise to a short vertebral artery supplying the vertebral column,
a oesophageal artery supplying the crop
and the oesophagus; and a long prominent
cutaneous artery supplying the skin and
muscles of the region of the neck.
About an inch posterior to the head the
carotids leave the groove and move forwards
and sideways, and opposite the angle of
the jaws each divid~s into two. The ou~er
branch, the external carotid supplies the
tongue, the muscles of the jaws and other
parts of the head; whereas the internal
carotid artery supplies the br~in.
,ii) The subclavian
artery is the largest to
arise from the innominate' it runs forward
just a little and divides into two:
(1) The brachial runs straight outwards to the
:wing giving a distinct, though delicate,
branch to the shoulder girdle.
(2) 'l'he pectoral artery is a large and' -'prominent vessel that turns towards the posterior
side and looping round the antero-lateral
region of the sternum, enters the great
pectoral muscle, which it supplies.
Ib) The right innominate gives out
similar branches.
exactly
7
THE PIGEON
(c) The dorsal aorta.
Push tlte viscera to one side and cut off the peritoneal
covering to expose the aorta. Be careful ?wt to C1t~ ale
arteries supPlying tlze mesentery.
The aorta arches over to the right side and rUIl>!
backwards crossing the right pulmonary. Then it runs
backwards in the mId-dorsal line giving off the following
branches : (i) The coeliac artery, a median vessel, arises
just as the aorta emerges below the ventricle.
It supplies the stoma ch, gizzard and part
of the intestine.
(ii) The a!1terior mesenteric arises about a
quarter of an inch posterior to the coeliac
artcry, nms back into the mesentery and
supplies tllP intestine.
(iii) The anterior renal arteries are a pair of
small vessels arising from the aorta, a little
anterior to the first lobe of the kidneys.
Before entering the substance of the anterior
lobe of the kidney each gives off a branch
going to the testes in the male, and in the
femate only the one on the left side gives off
a branch supplying the ovary.
(iv) The femoral arteries are a pair of prominent
blood vessels arising opposite the anterior
lobes of the kidneys. Each passes outwards
in between the anterior and middle lobes
of the kidney, and supplies the muscles of
the thigh. Before emerging through the
pelvic girdle each gives rise to a delicate,
though quite long blood vessel, the pubic
THE PIGEON
99
artery running along the ventral borner of
the pubic bone.
.(v) The sciatic arteries are a pair of prominent
vessels arising opposite the middle lobes of
the kidneys and passing outwards between
the middle and the last lobe of the kidneys.
After passing through thO":l ilio-sciatic foramen
each supplies the muscle of the thigh on the
inner side.
./
(vi) The middle and posterior renal arteries
are two blood vessels arising from the sciatic
on each side. The middle renal supplies
the middle lobe of the kidney and the
posterior renal supplies the posterior lobe.
",'vii) The posterior mesenteric artery is again
a median artery supplying the rectum and
duaca and arising from the aorta opposite
the hil}der end of the kidney.
(viii) The internal iliac arteries arise almost at
the same place as the posterior mesenteric
and runs behind to the hinder part of
the pelvis.
~ix)
U.
The caudal artery is the terminal portion
of the aorta going to the caudal vertebrae
and the pygostyle.
Dissection of the Heart.
Remove the heart by cutting 0if the vessels about a
Dissect it under water. First
slit ztp the outer walt of the auricles with scissors, wash out
the contents and examine the following :
1Juarter of an inch from it.
100
A
THE PIGEON
The
ri~ht
auricle.
(i) The openings of the venae cavae are threelying close to each other.
(ii) The eustachian valve is a muscular fold
on the right side of the opening of the pos·
terior vena cava.
(iii) The septum auricularium, the interauricular septum, is the thin muscular partition
between the two auricles. It bears an oval'
patch, the fossa ovalis, at the position.
occupied by the foramen ovale in the em·
bryonic stages.
(iv) The ri~ht-auriculo-ventricular
aperture
is the crescentic opening of the auricle into'
the ventricle.
B.
The left auricle_
(i) The openings of the pulmonary veins
are in a small recess of the dorsal wall of
the auricle.
(ii) The left-auriculo-ventricular aperture is
the circular opening of the auricle into the
left \-eutricle.
C.
The Ventricles.
Cttt transversely across the ventricles, abozlt the tiP, and
examine. Expose tlte ventricles fttlly later on.
(a) The right ventricle is thin-walled and
wraps around the left ventricle. In transverse section it appears crescentic, lodging
the left ventricle in its concavity.
THE PIGEON
101:
{i) The auriculo-ventricular
valve formed of
two muscular flaps is connected to the
ventricular wall at the base of the origin
of the pulmonary artery.
{ii) The aperture of the pulmonary artery is a. t
the extreme anterior end towards the left side
of the ventricle. Guarding the entrance 01
the artery are three semi-lunar valves.
(b) The left ventricle has thick spongy walls
enclosing a somewhat circular cavity. It
carries:
(i) The
left auriculo-ventricular valve {the
mitral valve) consisting of three muscular
flaps projecting into the ventricle.
(ii) The aperture of the aorta sitnq,ted at
its anterior end slightly towarris its right
side. This aperture is also guarded by three
semi-lunar valves.
,6.
RENAL AND REPRODUCTIVE SYSTEM.
A.
The Male Pigeon.
T.
The Renal System.
(i) The kidneys are two, each of which is
divided into three lobes. They lie in the
body cavity behind the lungs a,nd :He
covered over by the peritoneum.
(ii) The ureters are straight narrow tubes each
of which arises from the anterior lobe and
emerges between the anterior and middle
102
THE PIGEON
lobes. Thence, it runs backwards along th0'
inner side and ventral surface of the middl0'
and posterior lobes to the dorsal wall of thfr
cloaca.
(iii) The adrenals arE' a pair of elongated yellowish bodies attached to the anterior ends
of the kidnE'Ys.
II. The Re productive System.
(i) The testes are a pair of oval bodies lying
in cont~ct with the ventral surface of the
anterior lobes of the kidneys.
(ii) The vasa deferentia arc a pair of tubes
with opaque walls emerging from the inner
sides of the posterior ends of the testes. They
run back along the outer edges of the ureters. In the breeding season their hinder
ends are swollen to form the seminal vesicles, just before they open into the cloaca.
(iii) Thc cloaca is a tubular portion divided
internally into three compartments.
Cut open the ventral 22'all of the cloaca and examinlJ
carefully.
(a) The coprodaeum is the anterior portion
that is pushed towards the ventral side.
Tho rectum opens into this port,ion.
(b) The urodaeum is the next compartments
into which oprn the urinary and genital
ducts.
c) The proctodaeum is the last portion opening externally. A thick-walled glandular
THE PIGEON
103
vouch, the bursa Fabricii, that lies against
the dorsfi,l wall of the cloaca (in young birds
only), opens into the pro0todaeum.
R.
I.
IT.
The Female Pigeon.
The .renal system is the same as described above.
The Reproductive System.
(a) rrhe ovary is only one on the left side in the
adult. (In the embryonic stage both the
ovarks are present but in the adult the
right one atrophies). It is an irregular
tlh!L}led body lying intI'ont of the anterior
lobe of the left kidney. It is loaded with
ova.
(b) The oviducts are two, the left of which,
being functional, is wide convoluted tube.
Anterior·y it becomes, t,hin-walled and opens
, by a long oblique mouth, forming 'a sort
of funnel lying in close contact with the
ovary. Posteriorly it opens into the cloaca.
The right oviduct is abortive.
7.
DISSECTION OF THE BRAIN.
Remove the skht covering the head completely, with a
sharp scalpel, scrape off the bones nf the r60f and slowly
slice off the bones bit by bit. Good care must be taken as
-",'ou proceed with the dissection. The soft brain lies just
below the bmy roof. It may be injured by slight carelessness. After exposing the brain fully expose about half
an £nch of the spinal cord by removing the neural arches
of the first few vertebrae. Cut 0if the nerve roots and pic~'
11 p the brain. Place it in a watch glass and examine.
.tQ4
THE 1'1OEO.N
If the brain is soft enough for study place it in spirit
or a mixture of absolute alcohol and acetic acid for
at least twenty four hours or till it becomes com pletely
hardened.
A.
The Brain.
T. The dorsal view.
(a) The cerebral hemispheres are a pair of
large bodies occupying the median position.
Their surface' is smooth. They extend
backwards to meet the cerebellum and due
to their growth press the optic lobes outwards, which becoma lateral instead of
dorsal.
(b) The olfactory bulbs are extremely small
bodies projecting forwards from the anterior
end of tho hemispheres.
(c) The optic lobes are two smooth ovoid
bodies at the sides of the brain.
(d) The pineal body is a small oval body immediately behind the hemispheres lying in a
space between their median posterior angles.
(e) The cerebellum is of great size and has a
large median portion and two small lateral
lobes, the flocculi.
II.
(f) The medulla oblongata is thick ani wide
and shows ventral flexure. I t continues
into the spinal cord.
The ventral view.
(a) The optic chiasma is a crossing formed by
the optic nerves lying between the optic
lobes, slightly towards the anterior side.
THE
PIGEON
105
(b) The infundibulum is a small median process immediately behind the optic chi~sma.
B.
The Ventricles of the Brain.
Dissect the brain into two along the mid-ventralliue by
:means oj a sharp blade. The various cavities are very
.narrow and represented by almost simple grooves.
(a) The diocoel or the third ventricle is the
cavity of the diencephalon, which does
not appear externally due to the growth of
·the hemispheres and the cerebellum. It is
a narrow vertical cavity bounded laterally
by the optic thalami and opening infront
by the foramen of Monro into t.he paracoels or the ventricles of the hemispheres.
(b) The optocoels are th~ cavities of the optic
lobes opening in the centre into a narrow
passage, the iter, which is the cayity of
the mid-brain.
(c) The metacoel or the fourth yentricle i8
the cavity of the hind brain.
S.
THE SKELETON OF THE FOWL.
Owing to its larger size the fowl's skeleton is generally
for study in the class. Therefore, a description of
the skeleton of the fowl is given below. In fact the
.differences between the skeletons of the two animals
.are of a minor nature, and the following description will
practically apply to either.
.~iven
1. T.he Axial Skeleton.
The axial skeletons consists of tho vertebral column
..and the skull.
~OH
A.
THE PIGEOX
The Vertebral Column.
There are three characteristics of the vertebral column'
of a bird (i) the neck is long, being eqnal in length to·
the- remaining length of the column, (iiJ the trunk region
is rigid because the thoracic yertabme are fused, (iii) the
shortness of the tail; the number of vertebrae itself is·
short while the posterior ones fuse to form the pygostyle.
The vertebrae of a bird, and for that matter the entire
skeleton, is lighter as compared to the correspondingbones of other animals.
(I) The cervical vertebrae are the vertebrae of theneck region. In the birds it is difficult to distinguish
between the thoracic and the cervical vertebra. The
usual practice is to regard the first vertebra having itt~
ribs articulating with the sternum as the first thoracic
vertebra; all those anterior to it are the cervi..:als.
Cotmt the 1mmber of the cervicals in a mounted specimen'
and note.
(a) A Typical Cervical Vertebra.
(ii The vertebra is long as compared to the
vert~bra of the varanus.
(ii) The centrum is slender having saddleshaped surfaces, the anterior one being
concave from side to side and convex from
a hove downwards, while the posterior face·
is convex from side to side and concave
from above downwards.
(iii) The neural arch is shorter than thecentrum and is notched in the middle line
both anteriorly and posteriorly and the
neural spine is rudimentary.
•
(iv) The tt:ansverse processes are fused with
the cervical ribs forming a sharp back-
THE PIGEON
1077
wardly directed process having a foramen at
its base, through the foramen passes thevertebral artery hence called ycrtebrarterial
canal.
(v) 'rhe zyapophyses or
are in two sets:
the articular
facets
The pre.zygapophyses are flat articular
facets on the anterior side, facing upwardsand inwards.
The post-zygapophyses are the posterior
articular facets projecting backwards from!
tho posterior border of the neural arch,
and facing downwards a.nd upwards.
(b) Special Cervical Vertebrae.
(i) The atlas or the first cervical vertebra isa light bony ring just like that of tl)(' varanus. Its ventral portion is thickened resombling a centr~~ and is notched above to'
receive the o11Qntoid process of tho
axis. Its :tnterior side bears cup-like spaces
to pl'ovidt' articulation to the 0ccipital
condyle of the skull.
(ii) '1'ho axis is the second vertebra larger than.
the atlas and smaller than the rest. It has
no transverse processes and no rib", Its
ccntrum is produced in front into It slender
process, the odontoid process (compareits shape and position with that of the varanus).
(c) The remaining cervical vertebrae are structurally similar but for variation in size and the fact that
in thr binder most half a dozen cervical vertebrae the-
108
TH:E~
PIGEON
hypapophyses are well developed while the last two have
weIJ;leveloped vertebrae movably articulated to them.
J
(2) 'rhe thoracic vertebrae are five, the three
.ante,rior ones are fused With the last ct'rvical vertebra,
their centraJ arches and various processes are confluent.
"Centra of the anterior thoracic and the posterior cervical
are produced below into a compressed fenestrated plate
lor the attachment of the muscle,; of the neck. The fourth
.thoracic vertebra is free and the fifth fused with the first
sacral vertebra.
Sometimes there are <;mly four thoracic vertebrae then
the first three fuse to form a common mass, wher~s, the
fourth is free. All the thoraeic vertebrae carry ribs that
articulate with tIle' tlternu·m. Sometimes o~';) or two
cervical vertebrae also carry ribs but tht)',. do not arti.culate with thl> sternum.
(3) The synsacrum is made up of next fourteen to
.sixteen vertebrae fused together and supporting the
immense pelvic girdle. The anterior one bearing ribs
.articulating with the sternum is thoracic. 'fhen there
.are about half a dozen lumbar vertebrae followed bv two
.sacral vertebrae with sacral ribs. The compound synsa'Crum is so intimately fused that it becomes difficult to
-distinguish the bones clearly. Last portion of the synsa.crum consists of fused anterior caudal.
(4) The caudal region is short consisting of six to
seven movable vertebrae of which the last consists of a
vertical, laterally compressed plate, the pygoetyle.
(5) The ribs and the sternum.
(i) The ribs are flattened bony rods attached
to the thoracic vertebrae by two processe<;
THE PIGEON
109'
ta) the capitulum attached to the centrum,
and (b) the tuberculum attached to the
transverse process of the neural arch. The
ribs are united to the sternum by a sternal
portion. The vertebral portion of the ribs
carry backwardly directed bony proce~ses,
the uncinate processes, each of which runs
backward to the next rib and lies over it.
(ii~
The sternum is a broad bonp covering not
only the thorax but a great part of the
abdomen. Ventrally -it bears a projeQting
keel-like crest or carinA with which the
great pectoral muscles are attached. The
body of the st,ernum is boat-shaped and
consists of the following important parts.
(a) The manuorium is a small plate-like structure projecting vertically from the anterior
end of the ventral surface of the body.
~b)
The cal'ina or keel is the ventrally projecting triangular bony plate.
(c) The meta-sternal processes are a pair
of large processes on the sides of the anterior
end of the body of the sternum. Each of
them called a metasternum is direct,ed backwards and is divided into two flattened
processes one of which lies just behind the
last sternal rib and the other projects freely.
(d) 1'he costal surfaces are depressions in the
lateral borders .of the 'body with which articulate the sternal ribs.
Anteriorly thecostal surface is. drawn out into a costa'
process on each side.
lIlO
THE .PIGEON
(e) The coracoid grooves are deep transverse
grooves, lying about the base of the manubrium and communieating with each other
through ,a hole. These provide articular
facets for the coracoid bones.
J3.
The Skull.
The bones.of the skull of a bird are fused so intimately
tthat, in the adult condition, it i8 difficult to make out
their outlines. Besides the orbits are large and the face
is protonged into a long conical toothless beak; the occipital condyle it; one and only one ear ossicle, the columella,
_,is present.
(1) The cranium is rounded having usual bOiles for.ruing it..
(i) The Q~~ipj_tal region has basioccipital
(base), exoccipital (sides) and supraoccipital (top), all of which enter into the
foramen magnum, but the notched occipital condyle is formed by the basioccipital
alone.
(ii) The parietal region has well de';relopcd
basisphenoid (base), the alisphenoids
(sides) and the ankylosed parietals (roof)
On the ventral aspeot of the basisphenoid
paired membrane bones, the basi temporal
are developed and beeome firmly ankylosed
to it in the adult•
•(iii) The frontal region. The presphenoid (base)
the
interorbital
septum
enters into
and, therefore, is not, distinguishable. The
orbitosphenoid (sides) are very incons-
THE PIGEON
III
picuous bones entering into the interorbital
septum but they ean be easTIy made out in
a sagittal section. The fronta~l'e quite
proniincnt and extensive bones. The broad
posterior end of each frontal is drawn out
III a post-orbital process.
(2) The iympanic cavity is a cup shaped cavity at
the side of the hinder end of the cranium. It is bounded
by the squamosal above and the bn,sitemporal below.
(i) The fenestral recess is an oval dppression
within the tympanic cavity, almost, in t11e
middlp, ani divided by a partition into an
UPPE'l' fenestra ovalis, and a lower fenestra
,rotunda.
'
(ii) The posterior opening of the eustachian
canal is' a funnel-shaped opening at the
ventral and anterior end of thc tympanic
cavity.
(3) The orbits are large spaces separated from each
other by the interorbital septum which i~ formed mainly
lby the mesethmoid helped by the presphenoid and
orbito sphenoids. Below the interorbital septum is a
..rodlike thickening of the basisphenoidal rostrum.
Dorsally it is bound by the frontal and anteriorly by
the frontal and lacrymal. The lacrymals are large and
,each is produced downwards at the anterior end into a
slender curved process. Below the orbit is incomplete.
The intprorbital septum is fenestrated.
Locate the
following important fenestrae:
(j) The foramen for the exit of the olfactory
nerve is a median opening at the anterior
,end of the oranium which is continued
112
THE PIGEON
forwards as a horizontal slit betwefn thE"
inter-orbital septum and the frontal bone.
(ii) The optic
foramen is the large median
hole in the orbitosphenoid bones opening
into the posterior part of the orbit.
(iii) The foramina for the exit of the third'
and fourth nerves are small holes towardsthe outer side of the optic foramen.
(4) The olfactory capsules are relatively smaller in
size.
(i) The nasals are a pair of lamellar bones
which cover the sides and roof of the olfactory capsules. Posteriorly they are fused with
the frontals while anteriorly they becamenotched forming the upper and lateral
boundaries of the external nares.
(li) The vomers are two but they unite into a
single bone which is extremely small and
found in continuation of the rostrum. It is
often removed while cleaning the skull
unless done cautiously. In the pigeon the
vomers are not prrsent.
(iii) The ecto-ethmoid or turbinals are poorly
developed. The internasal septum is a
cartilaginous continuation of interorbital
septum. All these structures being entirely
- cartilaginous are removed while cleaning
the skull.
(5) The Maxillo-palatine Apparatus.
(i) The premaxilla is a large triradiate bone(really speaking formed by the fusion of
THE PIGEON
113
two premaxillae) forming practically the
whole of the upper beak. rtf! ascending
nasal process runs backwards completing
the upper boundary of the external nares,
whereas, the two maxillary processes run
. backwards and slightly outwards formin~
. part of the margin of the upper jaw.
(ii) The maxillae a~e slender bony rods, each
of which lies behind and to the inner side
of the maxillary process of the premaxilla.
Anteriorly each is expanded into a thin
horizontal lamina, the maxillo-palatine
process, with which the palatine is
attached ventrally.
(iii) The infra-orbital arcade is a slender bar
below the orbit formed by the union of
three bones-anteriorly a process of the
maxilla that runs behind and joins another
slender rod, the jugal, which meets the
quadratojugal posteriorly. These are the
components of the sub-orbital bar or the
infra-orbital arcade. Posteriorly the quadratojug~l is thickened and articulates with
the outer side of the distal end of the
quadrate.
(iv) The palatine is a slender horizontal bar anteriorly attached with the ventral aspect of
the maxillo-palatine process and posteriorly
it is expanded into a broad lamella the.
sides of which articulate with the rostrum,
whereas, its posterior end articulates with
the pterygoid.
8
11-1
THE PIGEON
(v) The pterygoids are stout rod-shaped bones,
each of which is set obliquely articulating
behmd with the inner surface of the quadrate and infront with t:le rostrum and
palatines.
(6, The Suspensorium.
(.i) The squamosal lies above the tympanic
cavity and is firmly fused with the bones
of the cranium at the s:ldes of its bulging
posterior part. The zYI~omatic process
of the squamosal is a thin bar projecting
forwards and downwards. Distally it fuses
w:th the post-orbital process of the frontal.
(ii) The 'quadrate is a stout triradiate bt'ne.
Its dorsal arm articulate:s with the squamosal slightly above the anterior border of
the tympanic cavity. Its flattened ventral
arm runs ventrally along the outer side of
the pterygoid and articulates with the
quadratojugal. Its transversely expanded
lower end provides the articular surface
for the lower jaw. The third or anterior
arm of the quadrate runs inwards parallel
to the pterygoid. Its anterior end lies free.
~(7) The lower jaw consists of a pair of long laterally
compressed rami firmly united in front. Each is thickened
and expanded giving a process inwards. at the hinder end
with which it articulates with the quadrate.
-------~
--------
Each ramus of the mandible really consists of tive
bones, OI!~ )"e'pla,_ci~~ _bone the articular and ~
i!1g bones., the angular, supra-angular, dentary and
splenial, all having the same general relations as in the
lizard. But these bones can be studied only in the
mandibles of the young bird.
115
THE PIGEON
(8) The hyoid apparatus consist.s of a short. arrowshaped body, the basihyal, bearing two pairs of cornua.
The anterior cornua or ceratohyals are short. The
posterior. cornua tlt thyro-hyals, lying further back,
. are a long pair of joint.ed process.
There are t.wo small basi-branchials, one a short
rod connect.ing the two cornua with the basihyal and the
other is a pointed rod projecting in betw~en the posterior
cornua.
(II) Tht' Appendicular Skeleton.
A.
The Pectoral Girdle.
The pectoral girdle consists of a scapula, a coracoid
,and a clavicle.
,
(a) The scapula is long flattened sabre-shaped
bone lying along the dorsal side of the
thoracic frame·work, almost parallel to the
vertebral column. Its expanded anterior
end is firmly united with the coracoid by
ligament. On its outer side it hears a shallow
depression forming a part of the glenoid
cavity. The glenoidal end of the scapula
is produced into an acromial process, to
which the clavicle is attached.
;I'
(b) The coracoid is a stout straight bone
directed ventralwards and it articulates
with the coracoid groove on the anterolateral edge of the sternum. On its outer
side it bears a cup-shaped depression COllipleting the glenoid cavity. The corltcoid
is also produced into a process directed
upwards and inwards. The clavicle is
116
THE PIGEON
attached with this proeess. Thus also a..
foramen, called the foramen triosseum,
is left between the thre,e bones, through
which passes the tendon of the subclavius
for insertion into the back of the humerus.
(c) The clavicles are a pair of slender curved
bones connected by their expanded upper
ends with the coracoid and scapula, as
mentioned above. Ventrally the two clavicles fuse forming a laterally compressed
rounded plate. The bone thus, formed is.
the "merry-thought" bone- or the furcula..
B.
The Fore-limb or Wing.
(a) The arm.
/ t h e humerus is an elongate bone' expanded
at both the ends. Tne head is expanded
and fits into the glenoid' cayity. The head
is bordered by preaxial and postaxial'
tuberosities. From the preaxial tuberosity
extends a short deltoitd ridge. The postaxial tuberosity is larger and has a pneumatic foramen close to it on the proper
dorsal face of the proximal end.
Distally the trochlear end of the humerus'
articulates with the bones of the fore arm.,
(b) The fore arm oonsists of t.wo bones the rndius:
and the ulna.
(i) The radius is a slender- bone articulating'
with the t!'.9.C.h!.ea.!lL~!:e humerus. proximally
and the oarpus distally -: - -_ - ~ ~ - -
-- --...._..
THE PIGEON
117
I{ii) The ulna is stouter than the radius and
also larger. A small olecranon process
projects from its proximal end beyond its
articular facet for the trochlear end of the
humerus.' Distally it articulates with
the carpus.
(c) The carpus consists of only two bones in
the adult (in the young birds the
distal carpal row consists of three pieces
which later fuse with the metacarpus). Of
these the ulnare articulating with the ulna.
is the larger whereas the radiale is smaller.
The manus in the adult consists at a carpo:metacarpus formed by the fusion of meta.carpals with the distal ro\v of carpals. It
'consists of two rods, the proximal of which
'is the stronger of the two, and more or less
straight. This represents the second meta'-carpal with the base of which is fused the
first metacarpal. With the first metacarpal
articulates a single pointed phalanx of the
first digit. Distally the stout rod bears two
prominent phalanges of the second digit.
'The third metacarpal is represented by
-thl:' thinner, slightly curved rod on the
postaxial side and carries a single pointed
'
phalanx of the third digit.
'D. The Pelvic Girdle.
The ilium, ischium and pubis, the three common
{!omponents of the pelvic girdle are present in this case
also though in an entirely different form. All the elements
@f each side are perfectly fuse..d_ with themselves forming
the os innomin~umJ both of which fuse with the
lIS
THE PIGEON
synsacrum in between, forming a more or less, shield· shaped'
structure covering the organs of the body cavity from
above. As usual, the acetabulum, for the articulation of
the femur, is present a.t the junction of the three bones.
Each half of the girdle consists of the following parts.
(i) The ilium is a rem8rkably expanded bone
extending both anterior to the acetabuluill'
and also posterior to it. The inner border
of the ilium is fused with the synsacrum,
whereas, the outer surface of its anterior'
part is concave. Posteriorly it is fused with
the ischium. On the outer surface, above'
the acetabulum, is a projection, the antitrochanter that articulates with the great
trochanter of the femur.
(ii) The ischium is directed backwards parallel
to the hinder part of the ilium to which it
is attached posteriorly enclosing, just behind
the acetabulum, an oval iliosciatic foramen.
(iii) The pubis is a slender bone directed back-
wards parallel to the outer and ventraD
margin of the ischium, with which it is
often fused. Behind the acetabuillm the
pubis and ischium is separated by a slitlike opening the, obturator foramen.
(iv) The acetabulum is formed by all the three
bones and is perforated. It is a rimmed
cup-like depression for the articulatIOn of
the head of femur.
D.
The Hind-limb.
(a) The
Thi~h.
THE PIGEON
119
(i) The femur is a short and powerful bone
enlarged at both ends. The rounded head
is proximal, on,. the outer (postaxialJ side of
which is an irregular process, the great
trochanter, With which bone the great
trochanter articulates? ) t...tA v.."", 'l ~ to.~..
QJ~~'"
~
t'; '_
(b)
Distally the femur presents infront a deeply
~~rooved surface for the patella, which is
a sesamoid bone forming the knee-joint.
f'2'"-P
The Leg or Crus.
(i) The tibio-tarsus is a long Done forming the
crus. It is chiefly composed of tibia fused
with the proximal row of thl? tarsus. The
proximal end of the tibio-tarsus is expanded
and has on its anterior face a great ridge
th~ cnemial crest. Distally it articulates
with the tarso-metatarsus by a pullylike articular surface.
(ii) The fibula is reduced to a slender bone
_ closely applied to the outer surface of the
tibio-tarsus.
(0)
The tarsus has no free bones in the adult.
The proximal row of tarsus is fused with
the tibia and the distal with the meta tarsus.
The ankle joint, therefore, is between the
proximal and distal rows of tarsal bones,
(a mesotarsal joint).
(d) The tarso-metatarsus is a stout long bone
proximally articulating with the tibio-tarsus
and distally bearing three meta tarsals
separate from each other, pach articulating
with a corresponding digit. Besides another
120
THE PIGIWN
incomplete metatarsal, the first meta.tarsal, is present for the hallux. It is a.
small irregular nodule of bone attached
to the inner and posterior surface of tarsometatarsus.
Note: The tarso-metatarsus in the male often bears a
pointed spinous fighting spur.
\ e) The phalanges are
proportion as in the
directed hallux has
thr.ee, the third or
the fourth toe five.
present in the same
lizard, the backwardly
two, the second toe
middle toe four and
CHAPTER V
THE RAT
A.
EXTERNAL FEATURES.
Examine the specimen placed before
YOlt.
(a) Notice that the body is covered with soft
fur. How does the exoskeleton of the rat
differ from that of the fish, varanus or the
pigeon?
Note the absence of hair from the muzzle, the external
<ear, feet and tail.
(b) The body can be divided into four regions,
the head, the neck, the trunk and the tail.
1. The head.
Notice its general shape.
(a) The mouth. Did you notice any lips in the
fish, varanus and bird? Does the rat have
lips? What is the difference between the
upper and lower lip ?
(b) The nostrils.
Notice their shape and
position and compare them with those of
the other animals studied by you.
{c) The eyes are dorsolateral. Compare their size
and position with those of the fish, varanus
ani the bird. Are there any eye-lids or
121
12~
THE RAT
eye-lashes? Notice a fold of skin at theinner corner of the eyes. This is the
nictitating membrane. Hold an edge of
t'c with a pair of forceps and pull it across
the eye-ball. What hap pens?
Id) The external ear or pinnae are at the
base of the head, each pinna is large
directed antero.laterally. Note the absence
of hair from the external ear.
(e) The vibrissae or whiskers are long hairs
developed on the face at the \lide of the
snout. Touch the v£brissae of a living rat (if
possible) and notice what happelts~ The
vibrissae are of four types according to
their positions:
(i) The mystacial vibrissae are those on the
upper lip between the eye and the muzzle.
The anterior ones are short and increase inl
size posteriorly.
(ii) The superciliary vibrissae are much shorter
about five, usually, and located above
the eye.
(iii) The genal vibrissa is a single slender vibrissa.
located below the eye.
(iv) The submental vibrissae are numerous,
slender and situated on the chin.
. 2. The neck is short and thick set without prominent
features.
3. The trunk is the largest part of the body. The
trunk of the rat is divided into the thorax and abdomen.
Supporting the trunk are two pairs 6f limbs.
THE RAT
123
1.
The fore·limb or arms include \ the upper
arm, the fore arm, and the hand. The
hand consists of the palmer region and the
digits, four in numbef. The first digit or
thumb is greatly reduced. What difference.
yO\! find between the fore·limbs of the rat
and other animals studied by you?
II.
The hind limbs or legs consist of the
thigh, the shank, and the elongate foot
composed of the planter region and the
digits, five in number. Compare the hind
limbs of the rat with those of the fish, the
lizard and the bird. To what special use
are the limbs modified in all the cases?
III.
The Apertures on the Trunk.
(a) The teats or mammae. If your specimen is a
female you will find four or five pairs of
small papillae on the ventral side of the
animal. These are the milk giving glands
by which the female supplies its young with
nourishment.
(b) The anus is a small median aperture below the
base of the tail.
(c) The perineal pouches are a pair of depressions on the sides of the anus and slightly
infront of it. The ducts of the perineal
glands open into these.
(d) The urino-genital openings are situated
infront of the anus in both the sexes.
(i) In the male the opening is at the tip of a
cylindrical penis. The tip of the penis can be
124
THE B,AT
retracted into a loose sheath of skin, the
prepuce.
(ii) In the female the opening is a longitudinal
slit known as the vulva.
l
4. The tail of the rat is elongate, cylindrical 'lUd
tapering and often slightly longer than the body. It is
devoid of hair though covered with overlapping scales.
B. DISSECTION OF THE ABDOM[NAL VISCERA.
Lay the rat in a tray, keeping the ventral side of the
animal uppermost and nail down the feet after stretching
them to their fullest extent. Feel the position of the ribs
and mark the limits of the thorax and abdomen. Cut the
body wall along the middle line ttpto the hinder end of the
thorax. Cut along the ribs dorsally on either side .md pin
the flaps. Do not open the thoracic cavity till a later
stage.
Note the position of the following organs :(1) The liver is a dark-red body at the anterior end
How many lobes are there? Find
the gall-bladder.
.of the body cavity.
(2) The stomach lies below the liver.
.and position.
Note the shape
Disentangle the intestine and spread it on the table
and measure its length.
(3) The duodenum is the initial portion of the intestine. Compare with that of the other animals.
(4) The small intestine is next portion after the
duodenum.
125"-
THE RAT
Follow the intestine backward till
where a short tube is given off.
YOII
come to a place-
(5\ The coecum is a blind comma-shaped outgrowth
at the junction of the intestine and large intestine.
(Note: In the rabbit the coecum ends in a tail-like
structure, the vermiform appendix; in the squirrel it is<
represented by a mere protuberance and so also in the
rat.)
(6) The colon begins following the coecum.
the first portion of the large intestine.
It is"
(7) The rectum is the last part of the alimentary
canal and is found dilated at intervals by faecal pallets.
(8) The urinary bladder is a thin-walled sac at the
posterior end of the abdomen.
(9) The spleen is a dark-red elongated body attached
to the posterior side of the stomach. Recall the size,
shape and position of the spleen in the other animals.
studied by you.
(10) The kidneys. 1'heyare a pair of compact bodies:
having the shape of bean seeds. They lie very closely
attached to the dorsal wall of the abdomen. The right
kidney lies behind the li~er. Is the left in line with it?
Compare the k,idney with that of the dog-fish, varanus
and the pigeon. tii front of each kidney lies the adrenal
body.
(11) The diaphragm is the muscular partition
separating the thClrax from the abdomen.
(12) The peritoneum is the lining membrane of the
abdominal cavity. The alimentary canal is supported by-
1~6
THE RAT
a double fold of peritoneum called the mesentery reflected
from the rlorsal waH of the abdomen.
C.
THE DIGESTIVE SYSTEM.
a.
The oral passage is the first division of
the digestive system opening to the exterior
through the mouth.
rOpen the mouth cavity as
fully as possible and
:'lOte the following.
(i) The
mouth is terminal, relatively small
and is guarded by movable lips, the upper
of which is cleft in the middle to exp0se the
incisor teeth .
.(ii) The teeth are present on both the upper
and lower jaws. There are a pair of molars
in each jaw. The incisors are long covered
and separated from the molars by a toothless region, the diastema .
. l iii) The palate forms the roof of the oral passage.
The anterior- part of the roof is formed by
the hard palate that separates the buccal
cavity from the nasal cavity. Notice the
transverse ridges on its surface. Posteriorly
the hard palate gives support to the soft
palatp which separates th(;;Oft naso-pharynx
with the buccal cavity.
{iv) The tongue is an elongate, thickened straplike muscular organ occupying the floor of
the buccal cavity. Its tip is free but the
body and root of the tOilgue are attached
by strong muscles to the hyoid bone.
THE RAT
(v)
127
The salivary glands are two pairs, the
parotid and the submaxillary. The large
parotid lies along the side of the head, in
the cheek, immediately beneath the external
auditory meatus; whereas the submaxillary
lies in the throat region just between the
angle of the mandibular bones.
(vi) The pharyngeal passage is a wide funnel.
shaped tube extending from the root of the
tongue and the posterior end of the soft
palate to the opening into the oesophagus.
The passage is both respiratory and digestive
in function. Posteriorly it opf'ns into the
oesophagus dorsally and the larynx vent·
rally. The entrance ~f the larynx, the
glottis; is guarded by t~e epiglottis. What
.do you think is the fUllctIOn of epiglottis?
'The internal apertures of the eustachian
.tubes also open into the pharynx. What is
.the function of these openings? .
.~.
.
The Alimentary Canal.
Since the abdominal viscera has already been exposed,
it will be better to study the digestive organs of the
,abdomen first. Trace the oesophagus later when the
thorax is dissected.
Expose the stomach by turmng the ltver upwards.
(i) The stomach is a sac-like expansion of the
digesti ve tract lying, on thf'\ dorsal side of
the abdominal cavity to the left of the
median line almost transversely.
The
strongly rounded region of the stomach iq
.the cardiac end, while the narrow cnd
128
THE RAT
leading to the duodenum is the pyloric end'.
that ends at the pyloric constriction.
C1tt open the stomach and wash away its contents and;
note.
The cardia or valvular arrangement at the
entrance of the oesophagus into the stomach, the sphincter ,muscles internal to the
pyloric constriction and also the glandular
internal lining of the stomach. <;ompare with_
the stomach of the dog-fish,the varanus and
the pigeon.
(ii) The duodenum is the proximal part of the
intestine, which takes the form of a V-shaped.
loop in th) mesentery of which is the ~!:an­
creas. The bile duct opens into the eXl'anded beginning of the duodenum and the
pancreatic duct into the distal limb of U.
(iii) The small intestine is the longest part of thealimentary canal forming coils as has been
examined before. What, is the advantage
of such a great length? The small intestine
ends in a rounded structure the sacculus
rotundus, the three way junction of the
coecum and colon.
(iv) The coecum is a tbin-wnlled diverticulum
for the storage of the partially rligested
food.
(v) The colon is narrower tube having sacculated_
appearance in the beginning and widens
out into a short rectum.
(vi) The rectum is the last portion of the alimen-tary canal. It is sbort and opens to theexterior through the anus.
'
129
THE RAT
C.
The Gland,s of Digestion.
(1) The salivary glands as described above.
(ii) The pancreas is a diffuse fat-like gland secreting pancreatic juice. Position and structure
has already been seen.
(iii) The liver is very large made up of five lobes.
(Compare with those of the dog-fish, the
varanus and the pigeon.) It is attached
to the diaphragm by a median vertical fold
of peritoneum, the suspensory ligament.
The gall bladder is an elongated thin-walled
sac lying between the right and left central
lobes. The main bile-duct arises from it
and opens into the duodenum.
D.
THE THORACIC VISCERA.
Make an incision where the ribs meet the diaphragm.
Cut away the nbs taking care .not to injure the organs that
tte beneath.
Note the following:
l. The thymus is a soft gland. like body lying on the
anterior part of the thorax.
2. The heart is enclosed within the pericardium. Cut
the pericardium and notice the external structure of the fottr
chambered heart.
3. The lungs are soft spongy masses of tissue lying
in the pleural cavity. In the rat the right lung is somewhat larger and is divided into four lobes. The left lung
is composed of flo single lobe.
9
130
THE RAT
4. The diaphragm is the muscular layer separating
the thorax from the abdomen.
5. The phrenic nerves are a pair of slender nerves
lying bt'tween the heart and the lungs. Trace them as
far as you can. Notice that the posterior end mt.>ets the
diftphragm. Do not mix these 'nerves with thp pneumogastric nerves which lie a little nearer the middle of the
thorax.
6. The pleurae. The lungs lie in the pleural cavity
and the glistening membrane lining this cavity is known
as the pleura. The right and left pleural cavities are
separated by a narrow median cavity, the mediastinal
cavity, in which the .heart lies.
7. The oesophagus is a muscular tube running
through the thorax immediately ventral to the vertE:.hral
column. It can be seen easily on lifting the left lung.
E.
DISSECTION OF THE OIROULATORY
SYSTEM.
I.
The Veins.
The veins are relatively superficial, it is important,
therefore, to dissect the veins before the arteries.
Remove the pericardium, expose the heart taking care not
to injure the blood vessels. EXlmine the important veins
opening into the right auricle and trace the branches opening
into them.
The venae cavae are three large hlood vessels return.
ing.the blood from the whole of the body to the ri'~ht
auncle.
). The right anterior vena cava or the right precaval returns blood from the right, side of the head and
neck etc. collected through these branches :
THE RAT
]31
(i) The right jugular vein that receiyes.--
(.a) The right external jugular vein from the
region of the lower jaw. It runs along the
side of the lower jaw at the angles of which
it turns inwards running along the side of
the neck.
~h) The right internal jugular vein that runs down
from the brain along the side of the trachea
and opens into the right external jugular
vein close to its ,union with the subclavian.
(ii) The
subclavian, a small vein collecting
blood from the fore-limb of its side and
opening into the precaval.
{jii) The
right anterior intercostal vein, a
small vessel collecting blood from the
intercostal spaces and opening into the vena
cava close to the auricle.
,(iv) The right internal
mammary vein,
another small vein running forwards on the
inner surface of the ventral thoracic wall
and opens into the vena cava opposite to
the first rib.
(v) The azygos vein, an asymmetrical vein
running in the mid-dorsal line of the thorax,
lying close to the vertebral column and
opening into the vena cava just behind the
right anterior intercostal vein.
2. The left precaval receives corresponding branches
from the left side except the azygos vein.
13~
'I'HE RAT
ARTERIE.S
_ •.INTERNAL CAROTID
': 'EXTERNAL CAROTID'
.• COMMO« CAROTID
"
:---SYSTE.MIC AORTA,
'.' "-PULMONAR'r
v--.,~-:..,,:.--'PIJLMONAR'1 AORTA,
.'
"
'>INTE.RCOSTAL
_.···COELIAC
'. -ANT-MESENTERIC"
__ - .' RENAL
.' GENITAL
Fig. H.-The circulatory system of the rat. The left
anterior vena cava has been removed.
THE
RAT
133
3. The posterior vena cava starts from the tail r('gion
:as the caudal vein and runs forwards close to the vertebral
column across the abdomen and thorax to open into the
posterior end of the right auricle. During its long course
.a number of other veins open into it. Beginning from
the posterior end of the body the branches are:
(i) The iliac veins are a pair of veins collecting
blood from the limbs and opening into tho
precaval in the pelvic region. Each iliac is
formed by the union of an external iliac
and an internal iliac. The external iliac
is the direct continuation· of the femoral
vein collecting blood from the outer border
of the thigh. The internal iliac collects
blood from the back of the thigh
(ii) The ilio-Iumbar veins are two, l'etu~ning
blood from the lumbar region.
{iii) The genital veins (the ovarian in the females and the spermatic in the males) are a
pair of veins returning blood from the gonads.
In the females they are small straight vpins
but in the males they are much longer and
directed backwards as they descend into the
scrotum along with the testes.
{iv) The renal veins are a pair of small veins
running from the kidneys to the vena cava.
(v) The hepatic veins are two relatively larger,
though short veins returning blood from
the liver lobes.
{vi) The phrenic veins are a pair of veins returning blood from the diaphragm just where
the vena cC.va crosses it.
134:
4.
THE RAT
The Portal System.
The portal system consists of the hepatic portal
vein formed by the uniltn of small blood vessels from the
intestines, pancreas, spleen and stomach etc. and opens.
into the liver by several branches.
The portal system 1S best seen in a fresh animal. OPen
the body cavity and turn the viscera aside and carefully
stretch the mesentery sttpporting the intestines and examine.
Draw a figure showing aU the vei1ls. Belter draw the
outline of vanozls parts and organs of the body and draw
the blood vessels in relatwn to them.
5. The pulmonary veins are two main veins reiurning blood from the lungs to the heart. They open into
the dorsal surface of the left auricle.
II.
The Arteries.
Locate the origin of the systemic arch as well as tlw
pulmonary arch. Trace along the systemIc arch and note
the blood vessels arising from zt.
1. The systemic aorta arises from the anterior end
of the left ventricle, passE's dorsal to the pulmonary aorta,
and then curves round to the dorsal side of the heart and
continues backwards as thE( dorsal aorta along the backbone. During its course arise the following main arteries.
of the body.
(A) The Anterio~ Branches.
Soon after the aorta issues from the heart it giveSl
off three branches the innominate, the left common
carotid and the left subclavian.
THE RAT
135
(i) The innominate is a very short artery soon
dividing into the ri~ht subc1vian and the
right carotid arteries.
,(a) The ri~ht subclavian artery runs straight
to the right forf-limb and gives a small
branch, the scapular to the shoulder, before
entering the limb where it is known as the
brachial artery. From the subclavian
also arise a vertebral artery going to the
vertebral column and another internal
mammary supplying the inner surface of
the ventral wall of the thorax.
(b) The right carotid runs forwards straight
along the trachea and near the angle of
the jaws divides into two-the internal
carotid artery going to the brain and the
external carotid supplying the right side
of the head and face.
(ii) The left carotid artery is similar to the right
carotid artery but for the fact that it arises
directly from the systemic aorta.
(iii) The left subclavian arises from the systemic
directly and supplies the left half of the
shoulder girdle and the left fore-limb. Its
branches correspond to that of the right
subclavian.
(B) Branches oj the dorsal aorta.
(i) The intercostal arteries are a series of
paired arterips supplying thE' wall of the
ch'_'st.
136
THE RAT
(ii) The coeliac artery is the first abdominal
branch of the aorta. It is a median blood
vossel arising ventrally and it supplies the
stomach and liver etc. through the lienogastric and hepatic branches respectively.
(iii) The anterior mesenteric is another median
artery arising from the aorta behind the
coeliac and supplies the intestines.
(iv) The renal arteries are paired arteries arising posterior to the anterior mesenteric and
supplying the kidneys.
(VI
The genital arteries are paired arteries
supplying the gonads. In the female the
ovarian arteries are small and pa '38 sideways supplying the ovaries, but in the
male the spermatic arterieS are long blood
vessels that pass backwards along the dorsal
surface and enter the. scrotal sacs through
the inguinal canals and supply the testes.
{vi) The posterior mesenteric is a median blqol
vessel supplying the hinder part of the
rectum.
fvii) 1'he ilio-Iumbar arteri~es are a pair of small
arteries arising from the aorta dorsally a11d
supplying the body wall.
~
(viii) The common iliac arteries are two a,risin
from the aorta in the pelvic region an
passing into the limbs. Each iliac artery
divides into an internal and an external
iliac .artery. Another branch of iliac on each
side, the vesical artery runs to the bladder.
THE RAT
137
(ix) The caudal artery is the continuation of
the dorsal aorta in the tail region.
2. The pulmonary artery arises from the anterior
border of the right ventricle in the mid-ventral line, arches
over to the dorsal surface of the left auricle and divides
into the left and right branches supplying the two lungs.
Follow the branches to the organs of their distribution.
Draw a neat diagram showing all the dissected arteries
faithfully.
III.
The Dissection of thE' Heart.
Dissection of the heart should always be attempted after
the dissection of the blood vessels and nerves of the neck.
After cleaning the roots of blood vessels remove the heart
along with a little length of each of the prominent vessel.
First examine its external characters, sketch and then dissect it.
(1) External Appearance.
The heart appears mainly to be formed by the
ventricular portion when seen from the ventral side, as
.the auricles lie at its base on its dorsal aspect.
(a) The auricles are two thin-walled chambers
anterior to and slightly dorsal, to the
ventricles.
(i) The left auricle lies to the left side almost
concealed by the prominent blood vessels.
Into it open the pulmonary veins from
the dorsal side.
(ii) The right auricle, on the other hand,
receives the three prominent venae cavae
dorsally.
l38
THE RAT
(b) The ventricles are thick-walled muscular
bodies separated by an oblique groove
cxternally.
(i) The left
ventricle is the largest of the
two lying behind the left auricle. Its walls
are thick. The aortic arch arises directly
from the left ventricle and conducts blood
to all parts of the body.
(ii) The right ventricle lies posterior to the
right auricle. It is a small chamber pumping
blood to the lUll!~s. From it arises the
pulmonary arch. ,Note: It will be very helpful to dissect the heart of
a goat or sheep for advantage of size. Differ-l'llces between the two are of a minor nature and can be easily
made out and noted.
(2) Internal Structure.
(AJ The Auricles.
Carefully remove the ventral wall of the auricles by Clt!ting
from the sides. Try to keep the aortic and pulmonary arches
as and where they are. Examine.
(i) 'rhe right auricle is a thin-walld chamber
mark~d internally by muscula,r ridges.
Into
the auricle open the three venae cavae by
separate' apertures.
(a) The eustachian valve lies between the
apertures of the two anterior venae cavae
and to some ext~n~ guarding that ofthe
THE RAT
posterior vena cava. It is a membranous:
told and 801r remnant of the right sinuauricular valve.
(b) The right auriculo-ventricular opening is
a wide crescentic opening into the right
auricle and is guarded by valves that will'
be described along with the ventricles.
(ii) The left auricle is a smaller chamber into'
which open the pulmonary veins by two
separate apertures. Posteriorly it opens into'
the left'ventricle.
(iii) The
interauricular septum completely
separates the cavities of the two auricles.
Almost ~n the middle of the septum is an
ill-defined depression, the fossa ovaHs. (In
the embryonic rondJtion the two auriclescommunicate with each other through an
apE'rture the foramen ovale, which is closed'
after birth leaving tht' above depression.)
(B) The Ventricles.
With the help of a sharp blade eltt off the ventral wall'
of the t'fl1trtcles, uash the ccntents and examine.
The walls of the ventriclp,s are thick and muscular.
The bundles of muscle fibres are so arranged as to form
longitudinal ridges, the columnae carneae projectingfrom the walls of the ventricle.
The interventricular septum is not entirely median
but inclined to the right leaving the apex to the left
ventricle.
140
a.
THE RAT
The Right Ventricle.
ii) The tricuspid valve consists of three flaps
and guards the right auriculo-ventricular
aperture.
(ii) 'rhe
opening of the pulmonary artery is
at the It'ft anterior angle. of the ventricle
and is guarded by three pocket like semilunar valves.
Cut open the pulmonary artery just at its beginning and
examine.
b.
The Left Ventricle.
(i) The bicuspid or mitral valve has only two
flaps guarding the left auricula-ventricular
aperture.
(in The entrance of the systemic arch
provided with three semi-lunar valves.
F.
THE URINO-GENITAL SYSTEM.
1.
The Male.
is
(a) The urinary organs. You have already
seen the position and shape of the kidneys.
Notice that they are surrounded by fat. The
notch to which the ureter is attached is
called the hilus. Trace the urete" and see
where it meets the bladder.
Take out one of the kidneys and bisect it longitudinally,
in the same way as Y01£ would sPlit a bean seed. Note the
following structures.
THE RAT
~i)
141'
The cortex or the outer layer.
(ii) The medulla or the inner layer. Observe
the conical structure, the pyramid, n9ar
the hilus.
(iii; The pubis is the broad portion of the
ureter which enters the kidney.
(iv) The urinary bladder is as described above.
(b) The reproductive organs.
\i) The scrotal sacs are a pair of pouches in
front of the anus and between: the hind legs.
Cut open the scrotal sac ventrally and expose
the testes lying in them. Note their sizes.
(ii) The testes arE! a pair of elongated ovoid
bodies attached to the hinder end of the
scrotal sac by a band of tissues, the gubernaculum. fln the very young rat the testes
lie in the abdomen close to the kidneys, just
before maturity they descend into the scrotal
sacs through the inguinal canals.)
(iii) The epididymes are a pair of irregular
masses of convoluted tubes lying along the
inner edges of the testes. At the posterior
ends of the t('stes it becomes, enlarged
forming the cauda epididymis and at the
anterior and it forms the caput epididymis.
From the cauda epididymis emerges on each
side the vas deferens.
(iv) The vasa deferentia are a pair of tubes
arising from the cauda epididymes. Trace
their path into the abdominal cavity through
the inguinal canals. In the abdominal cavity
i42
THE RAT
-each vas deferens loops round the ureter
from the outside before it opens into the
,urethra behind the bladder.
I..NUS
i
PERINEAL GLAND
Fig. 12.-The male urino-genital organs of the rat.
(v) The urethra or the urino-genital canal is the
common passage for urine and spermatozoa.
It leads into the penis.
(vi) The uterus masculinus is a blindly ending
sac, situated where the vasa deferentia and
urethra join. (It is the sole vestige in the
male of the Mullerian ducts.)
'vii) The penis is the organ for conveying spermatozoa into the body of the female where
THE RAT
143
the ova are fertilised. Tbe urethra opens
at the tip of the penis by a small slit-like
opening. The loose skin covering the tip,
the glans penis, is called the prepuce.
(viii) The prostate gland consists of several
lobes almost surrounding the walls of the
uterus masculinus and opens by small ducts
into the urino-genital canal.
{ix) The Cowper's glands ale a pair of glandular bodies placed on the dorsal wall of the
urino-genital canal, posterior to the prostates.
(x) The perineal glands are a pair of elonga-
ted glands lying on both sides of the penis,
in the anterior walls of the perineal sacs.
(xi) The rectal glands are a pair of yellowish
bodies lying on both sides of the rectum.
Draw a figure of the urilto-gellital organs of the rabbit
and label all the parts.
2.
The Female.
(a) The urinary organs.
,(i) The kidneys, the ureters and urinary
bladder are similar as in the male.
(Ii) The urethra is a long narrow tube runfiing
towards the posterior side and opening
independently at the tip of the clitoris.
·(b) The reproductive organs.
144
THE RAT
(i) rrhe ovaries are a pair of small yellow compact bodies about the size of a pea on either
side of the kidneys. 'They are suspended
in the body by a fold of peritoneum, the
mesovarium.
(ii) The oviducts are two, each divided into two
parts having different functions.
(a) The fallopian tubes are narrow convoluted
tubes having their anterior ends dilated into
the oviducal funnels. 'rhey convey the
ova to the uteri.
(b) The uteri are two' thiek-walled and dilated
ends of the fallopian tubes that meet in the
middle and form a common tube, the
vagina.
Fig. 13.-The urino-genital organs of the female rat.
Your specimen may have developing embrovs in which
case the uteri will be seen to be much distended. Cut open..
the uteri and examine the embroys.
145
THE RAT
(c)' The vagina it> a common tl}.be formed by the
fusion of the uteri from both the sides. It
opens to the exterior by a slit· like opening,
the vulva.
Note :-The vestibule or the urino-genital canal is
the common canal formed by the union of the urethra and
the vagina in the squirrel and the rabbit etc. It is very
short. It opens into the vulva, which is gUarded externally
by a pair of thick muscular lips. But in the rat the two
openings are separate.
(iii) The clitoris is a small rod·like organ. IJi
lies at the anterior end of the vulva. In the
rat the urethra opens at its tip.
Examine these organs carefltlly and draw a figure of
the female genital system of the rabbit. Label aU the parts.
G. DISSEOTION OF THE NECK.
T he dissection is made from the ventral side of the neck.
Kiep the parts moist while you work. Remove the skin
carefully·and expose the following structures.
1.
2.
The hyoid apparatus is deeply laid bet.
ween the two rami of the mandible .
. Expose the hyoid first, but take it out after
the dissection of the neck is completed.
The Blood Vessels of the Neck.
(i) The external jugular veins.
from the heart upwards.
Trace them
They lie to the extreme right and left.
10
146
THE RAT
(ii) The yarotid arteries lie along the side of
the trachea.
3. The trachea is the tube connecting the glottis
with the lungs. Trace it. Note the banded structure
on its ventral side. What do you think is the function
of these bands? Wby do they not extend on the dorsal
side also?
At the anterior end of the trachea is a dilated
larynx or the laryngeal chamb€lr whose walls are
supported by the thyroid arytenoid and cricoid cartilages. Posteriorly the trachea enters the thorax and
• divides into two bronchi going to the lungs.
4. The oesophagus is a muscular tube connecting
the gullet with the stomach. Trace the oesophagus without disturbing the nerves lying besides it.
5. The thyroid is a soft vascular. gland on either
side of the larynx.
6.
The Nerves of the Neck.
Carefully clean the carotid artery. Take special care
not to damage the nerves lying beside, stretch it to one side
and spread the surrounding connective tissue.· Find the
vagus or pneumogastric nerve rttnning on its outer side
follow it backwards along the neck and thorax and forwards
to the s kuZl.
The pneumogastric or vagus nerve is a stout nerve'
having a ganglionic swelling neal' its origin. H runs
downards from the foramen lacerum posterius until it
reaches the carotid artery and then straight backwards
along the neck lying outer to the earotid artery. In the
t,borax it runs along the oesophagus to the stomach.
THE RAT
147
(a) The anterior laryngeal nerve is a delicate
nerve arising from the pneumogastric opposite the upper border of the thyroid cartilage. It crosses the carotid artery and runs
dorsal to it. It bends anteriorly and innervates the mucous membrane of tIre larynx.
(b) The depressor nerve is a slender nerve
arisill;g from the anterior laryngeal. It runs
backwards along the neck lying dorsal to
the carotid artery. Trace it to the heart
where it ends.
(<0) The
right posterior or recurrent laryngeal arises from the pneumogastric just
above the heart then runs forwards alongside the trachea. Just after origin it runs
dorsal to the aortIc arch which obstructs it
from view. Be careful in locating it at this
place.
(d) ,The cervical sympafhetic nerve is a slender ne:rv.e that runs in between the pneumogastric and the depressor nerves. It swells
up into a small oval anterior cervical
ganglion at the level of the angle of the
jaw anteriorly, and posteriorly, into another
swelling, the middle cervical ganglion, lit
short distance infront of the subclavian
,artery.
(e) The phrenic nerve arises from the fourth
cervical nerve. It runs back along the vertebral column, and passing through the
thorax ends by a number of small branches
in the diaphragm.
Gently pull th.e ltmg and heart apart. Locate the conne·
.ction of the nNve with the diaphragm alld trace it forwards
to the place of its origin.
148
H.
THE RAT
THE BRAIN.
Tn contrast with the brains of the animals studied
thus far, it will be s'een in the mammals, that the cerebral
hemispheres are much enlarged, as lS also the cerebellum ~
there are four lobes on the roof of the mid·brain, and
the olfactory lobes are relatively small.
To take out the brain first remove the skiH and then
startlng from the foramen magnum cut along tf e sides of the
cranium carefully and finally Sntl' away the roof. The
brmn will be seen enclosed in a tough fibrous membrane,
the dura mater, which should also be removed. Expose about
an inch of the spinal cord by cuttmg away the dorsal half
of the vertebrae, Ilft up the whole stmctztre, thereafter, alollg
with half an inch of the spinal cord and keep it in a watch·
glass. If the brain 1S soft and pulP'Y Jzarden it in spirit
or in a mixtur.e of absolute alcohol and acetic acid iiI whIch
it must rematn at least for twenty fuu1' hours.
Examine the following parts.
(a) The fore·brain.
(i) The olfactory lobes lie at the anterior part
of the brain. Each of them consists of an'
olfactory tract and an olfactory bulb.
The olfactory traet lies on the ventral side
of the cerebral hemispheres. The olfac:tory
bulbs are large ovoid structures lying just.
anterior to the cerebral hemispheres.
(ii) The cerebral hemispheres are large pftired
structures separate along the median line
by a longitudinal fissure, the median
fissure. The surfa.ce· of the cerebral hemispheres is smooth in the rat. (In higheranimals it is thrown into folds and the hemi·-
THE RAT
149
spheres are divided into many lobes
by deep transverse and longiturlinal grooves
dorsally as well as ventra,lly). In the rat
they are more or less conical in shape pointed anteriorly.
(iii) The thalamencephalon is narrow and has
a stalk of the pineal body dorsally and
ventrally it carries the optic chiasma
and the illfundibulum which gives rise to
the posterior lobe of the pituitary body.
The anterior choroid plexus arises in the
roof of the thalamencephalon.
{b) The mid-brain contai.ns the optic lobes
represented by four rounded eminences, the
corpora quadri~emina,. on its dorsal
surface. Ventrally are found the crura
cerebri.
(c) The hind-brain consists of the cerebellum
and the medulla oblon~ata.
The cerebellum is next to th~ cerebrum in
largeness. J t is clearly divided into regions,
being made up of median lobe, the vermis,
and two lateral lobes each of which terminates laterally in the flocculus.
Ventrally is the much thickened medulla
oblongata. Extending transversely across
the under side of the medulla and connecting
the two sides of the cerebellum is a tract
of fibres forming the pons varolii. In the
roof of the hind brain is the posterior choroid
plexus.
150
THE RAT
(d) The Ventricles.
Cut a sagitt'll section of the brain by a sharp knife and
examine. The cavities in this case are much redllced.
(i) The rhinocoels in the olfactory lobes are
much reduced and almost invisible.
(ii) The lateral ventricles are narroW spaces ill!
the cerebral hemispheres. The lateral ventricles communicate with the third ventricle
by a more or less tra,nsverse passage the
foramen of Monro.
The hemispheres.
are connected with each other by a broad
transverse commissure, the corpus callosum, lying just int!,rnal to the base of
the median fissure. This will appear a'l a
longitudinal fibrous band just o\':r thO'
lateral ventricles in the section.
(iii) The third ventricle (the ventricle of thalamencephalon) is narrow laterally and passes backwards to the equally narrow iter into which
open the small cavities of the corpora quadrigemina, representing the reduced optocoel.
liv) The fourth ventricle i:3 the cavity of the
medulla into which opens the iter anteriorly.
I. THE SKELETAL SYSTEM.
For the study of the skeletal system of a mammalian
type the usual practice is to study the skeleton of the rabbitr
along with the skull of a dog. The sam~ procedure is
followed here.
(A) The Axial Skeleton.
1. The Vertebral Column.
The rabbit has about 45 vertebrae. In the mammalsin general the number of vertebrae in each region is fairly
THE RAT
1'51
constant. Each movable vertebra is separated by an
intervertebral disc, and all the vertebrae are classified
into five groups.
(i) The cervical vertebrae in
include the first seven.
the neck region
(ii) The thoracic or C;19st vertebrae are twelve
or thirteen in number and' are connected to
the ribs.
(iii) The lumbar or loin region vertebrae in the
abdominal region are six or severr in number.
(iv) The sacral or pelvic region vertebrae can·
SISt of three or four fused vertebrae which
support the pelvis.
(v) The caudal or tail vertebrae are twenty.
four or more in the rat and in the rabbit
they are sixteen.
You have already studied the- general characters of a.
vertebra before. Do you recognise thc centrum, the
neural arch, the neural spine, the transverse pro·
cesses, the pre-and post zygapophyses etc. ek. ?
(i) The Cervical Vertebrae.
(a) The first or atlas is ring-shaped. The neural spine is small and the transverse pro·
cesses are broad horizontal plates The two
concavities on the anterior face fit with the
occipital condyles of the skull.
(b) The second or axis has the centrum pro·
duced.anteriorly into the odontoid process,
which fits into the lower part of the ring of
152
THE
RA~r
the atlas. Th'l neural spine is elongated
and compressed. How is an odontoid process
formed? Compare the- structure of the
odontoid processes of the animals studied
by you.
(c) The characteristic feature of a ~ervical verte-
bra is that it has a canal, the vertebrarteriat' canal in addition to other common
structures This cana.l is formed by the
fusion of a cervical rill> with the vertebra.
(ii) The Thoracic Vertebrae.
Study anyone of the first six and find the following
parts:
1.
The centrum.
2. The neural arch.
3.
The transverse processes.
4. The neural spine.
5. The zygapophyses.
6. Articular facets for the
(b) the capitular.
rib~:-
(a) the tubercular
(iii) The Lumbar Vertebrae.
The lumbar vertebrae are comparatively larger. The
centrum .is stout, the neural arch is surrounded by a
prominent neural spine, the pre-and post zygapophyses
are as usual; and the transverse processes are stout, long,
flattened, directed obliquely downwards and forwards. At
the anterior eni are a pair of stout metapophyses, rising
well above the prezygapophyses, and below the postzygapophyses are the less prominent anapophyses.
THE RAT
153
the first two or three lumbar vertebrae a ventrally
directed projection the hypapophysis is present on the
under side. 'These prominent processes provide for the
.attachment of the muscles of the back.
t{)ll
(iv) The Saaral Vertebrae.
The sacral vertebrae are fused togather to form the
.sacrum which gives support to the pelvic arch.
(v) The Caudal Vertebrae.
The anterior caudal vert.ebrae resemble' the sacral,
but they diminish in size towards the tip of the tail till
only the centra are left.
Draw figures of the vari02tS vertebrae and write notes on
.each.
II.
The Ribs and Sternum.
(a) The Ribs.
Of the twelve or thirteen ribs the fifth may
be taken 3,S typical.
Each rib consists of a vert~bral portion
and a sternal portion. The vertebral portion is dorsal and bony. It has a tuberculum~ich articub.tes with the tubercular
facet of the tran:37erse process and a
capitulum which articulates with the
capitular facet of the centrum.
Draw a figure of a typical rib and label its parts.
(b) The Sternum.
It is. formed of six segments, the sternebrae, the first of which is called the manubrium. The last is long and slender, the
154
THE RAT
Xiphisternum and terminates in an expanded plate of cartilage, the xiphisternaL
cartilage.
Draw a figure of the sternum showing the manner in'
which the ribs are attached to it. Label the p'arts.
Fig. l4.-Diagram showing the arrangement of bones,
in the skull of a mammal.
(B) The Skull of the Dog.
To illustrate the characters of a mammalill,n skull that
of the dog is usually taken. In the present treatment
emphasis has been laid on the general characters of theskull, therefore, the des('ription can be safely applbd to
study the charact'jrs of the skull of rabbit with slight
adjustments here and there. Before proceeding study
fig. 14 that is a diagrammatic sketch showing the relation&
of various bones in the formation of the skull.
THE RAT
1.
155·
The cranium or the brain·box.
It is better to begin the study with the brain·bor
which is made up of three rings placed one after another.
The posterior-most ring is the occipital ring, the next
the parietal ring and anterior one is the frontal ring.
(a) The occipital ring is made up of (i) the
basioccipital, a flat median bone forming'
the base; I ii) the exoccipitals forming thesides; and, (iii) the large median supra
occipital that completes the ring dorsally.
(Note the difference in the shape of the'
supraoccipitals of the rabbit and the dog).
Between the exoccipitals lies the foramen
magnum, at the sides of which are the
occipital condyles.
Fig. 15.-Sagittal secti':)ll of the skull of the dog.
~
(b) The parietal ring l·ies just anterior to the
occipital ring and is made up of (i) a median
bone, basisphenoid, just infront of the
basioccipital, forming the base.; (ii) two large-
THE RA'I'
THE RAT
159
Internally the opening between the cranium and
<olfactory chamber is closed by the ethmoid in which is
the cribriform plate through the perforations of which
pass the fibres of the olfactory nerve. The cavity is
divided into right and left halves. by the partly cartilaginous mesethmoid the anterior end of which lies in the
internasal septum. The mesethmoid rests in the
y~shaped gutter on the upper margin of the vomer.
The greater part of the cavity is occupied by the very
'much folded turbinal or scroll bones.
(0) The optic capsules are represented by the
,orbit. The anterior wall of the orbit is formed by 'a
'Pair of lacrymals loosely wedged in between the frontals
and the maxillae and each has a small notch at its outer
border for the opening of the lacrymal duct. Jugal the
anterior portion of the zygomatic arch forms, the
,outer boundary of tho orbit.
3.
The Jaw •
.(.a) The upper jaw.
(i) The maxillae are two large irregular bones
bearin~ soc ets or alveoli for the teeth.
Ventrally the maxillq. is produced into a
horizontal plate·like process which meets
its fellow of the othpr side in the middle
forming a bony bridge supporting the palate.
These_procpsses are therefore called the
palatal processes.
~ii)
The palatines are a pair of horizontal plates
adding posteriorly to the bony bridge supporting the palate. (Tn thl:! rabbit they are
160
THE RAT
nearly vertical plates attaehed above to the
ventral border of the pre-sphenoid, and:
behind to the pterygoids and alisphenoids}.
(iii) The pte.rygoids are a pair of narrow verti-cal plates of bone attached to the base of
the skull at the junction of the basisphenoid
with the a1isph~noid.
,
(iv) The premaxillae are a pair of bone~ formiJg
the anterior part of the upper jaw. They
articulate with the maxillae behind, and
with each o~her in the inedian plane in front.
The upper and poster}or angle of each premaxilla is produced backwards into a long
nasal process which runs between the nasal
and maxilla.
(v) The zygomatic arch is an arch of bQ Ie extending between the maxillary and cranial
region of the skull on each side. The :lnterior part of the arch is formed by the jugal
bone and the posterior by the zygomatic
portion or process of the squamosal.
The two bone meet at an oblique suture.
(In the rabbit the jugal is fused with a·
process of the maxilla forming a process, the
malar, that forms the zygomatic arch with
the zygpmatic process (If the squamosal).
(b) The lower jaw.
The lower jaw consists of a single bone,
the dentary on each side, and the two
tegether are some times spoken of as forming.
the mandible. The lower jaw articdateswith the glenoid fossa of the squamosal.
Posteriorly the articular surface, however,
lies between two processes, the anterior
161
THE RAT
larger one, the coronary process, and the
posterior smaller one the articular process.
(In the rabbit, each ramus is flattened laterally and is comparatively broader. It bears
an incisor tooth infront and grinding teeth
behind. Between the two is a toothless
space.)
4. The hyoid apparatus consists of a median body of
the hyoid which lies at the base of the tongue between the
rami of the mandible. Anteriorly the body bears a pair
of'ar.terior cornua or ceratohyals and separate vestigial
stylo.hyals ; and posteriorly a pair of long backwardly
directed posterior cornua or thyrohyals are present.
5.
The Teeth.
The teeth in mammals are of different forms, heterodont. Those infront of the jaws are called the incisors
followed on each side by the canines, and then by the
cheek teeth made up of the premolars and molars.
(i) The incisors (the upper one of which are
always borne on the premaxillae) have a
sharp chisel edge and are used for biting
off the food as in the rabbit, but in the dog
they are used for prehension.
o
(In the case of the rabbit the wear on the
teeth being excessive the pulp cavity remains
open and the teeth continue to grow through
out life.
Such teeth are said to have
persistent pulp).
I
(ii) The canines are the characteristic teeth of
the dog. like mammals. They are larger,
11
162
THE JRAT
commonly concial and pointed, used for
seizing the prey. (In the rabbit they are
absent).
(iii) The cheek teeth usually have broader
crowns and the root has more than one fangs.
They are made up .of paemolars and
molars modified for grinding in some
mammals (e.g. rabbit), but in the dog the
last pair of premolars in, the upper and the
first molars in the lower jaws are pointedly
ridged and sharp edged, for shearing the
flesh, and are called the carnassial teeth.
(iv) The dental formu]a.
,
The number of teeth of each typO' varies in
different mammals and to represent this a
kind of equation called a dental formula
has been evolved ba,sed upon what is regarded as the typical number in the upper and
lower jaws on each side~
The following is the typical dental formula possessed
by the pig ..
i.
Dental formula of the dog.
" "
" "
6.
Rabbit
Man
~-, c-
i.~.
i.
t,
c.
f, pm. 1, ll.l.
~
= 44
h pm. t, m. i =
42
=
28
c. §, pm.
i. f, c. f, pm.
i,
m.
~
-L m. -~
= 32
Foramina of the Skull.
Locate the following foramina on the surface of the skull
andsketch.
THE
RAT
(i) 'The optic foramen is a large median hole
in the orbitosphenoids for the optic nerves.
~ii)
The foramen lacerum anterius is a
vertical slit below the optic foramen a bit
to ihe posterior side between the basisphenoid and the alisphenoid. It is for the
exit of the third, fourth and sixth nerves
and the maxillary and ophthalmic bran,ehes of the fifth cranial nerve.
,( iii) The internal orbital foramen is a small
aperture a quarter of an inch infront of the
optic foramen (exit for the nasal branch of
the ophthalmic of the fifth cranial nerve).
.(iv) The infra-orbital foramen is a prominent
aperture on the zygomatic process of the
maxilla (exit for the infra-orbital branch of
the maxillary of the fifth cranial nerve).
.(v) The anterior palatine foramen is a slit-like
aperture anterior to the palate just internal
to the incisor and separated from its fellow
of the other side by the palatal process of
the premaxillae (exit for naso-palatine
branch of the maxillary of the fifth).
(vi) The posterior palatine foramen is in the
bony palate at the junction of its maxIllary
and palatine processes (exit for the anterior
palatine branch of the maxillary of the fifth).
-(';vii) The foramen lacerum medium is between
the alisphenoid and the periotic just infront
of the tympanic bulla le~it of the mandibular
branch for tlw fifth)_
IG4
THE RAT
(viii) The stylomastoid foramen is about the
mid:lle of the posterior border of the t.ympftnic bone, between it and the mastoid
process of the periotic (exit for the seventh
.cranial nerve).
(ix) The foramen lacerum posterius is between
the occipital condyle and the tympanic bulla
(exit for the glossopharyngeal, pneumogastric
and the spinal accessory nerves and the jugular vein).
(x) The condylar foramina are holes in the
exoccipitals just infront, of the condyles
(exit for the hypoglossal nerve).
(xi) The lacrymal foramen is in the r.uter
border of the lacrymal bone t exit for
lacrymal duct).
(xii) The pituitary foramen is a median hole in
the centre of the basi-sphenoid.
(xiii) Th'1 carotid foramen is in the ventral
surface of the tympanic bone close to the
occipital condyle (passa€!.e for the internal
carotid artery.
Among other apertures of the skull are the
anterior narial openings, the openings of
the eustachian tubes the external auditory apertures and the foramen magnum
which the students are familiar with.
(B) The Appendicular Skeleton.
1.
The Pectoral Girdle.
The pectoral girdle is composed of
THE RAT
:3..
165
The scapula which is a triangular bony
plate, having at its apex the glenoid cavity
into which fits the head of the humerus.
The coracoid is fused with it giving a small
coracoid process or spur.
lb. The suprascapula is reduced to just a strip
of cartilage. On the outer surface of the
scapula is a ridge, the spine, the free vt'ntral edge of which has two projections, the
acromion process and the metacromion
process. The acromion is a free downwardly directed process, whereas, the mentacromion is a long process projecting backwards.
c. The clavicle is a slender slightly curved bone
running from the sternum to the scapula.
Draw a figure of the pectoral girdle and write down
the differences between the girdle of the varanus, the pigeon
.and the rabbit.
2.
The Fore-Limb.
(a) The arm consists of only one
humerus.
bone, the
Note the head of the humerus that fits into the
glt'noid cavity and also the trochlea with
a small hole called the supra-trochlear
foramen. Note the deltoid ridge.
(b) The forearm consists of two separate bones
immovably articulated. Both are almost
equal in size.
166
THE RAT
(i) The radius is an elongated bone, slightly
curvtd forwards, proximally it articulateswith the trochlea of the humerus and distally
with the bones of th{, wrist.
(ii) The ulna is the post axial oone of the forcarm. It has an en18>rgcd proximal end on
the anterior surface of which is the sigmoid
notch for articulation with the trochlea.
Behind the elbow-joint, the bone forms the
large laterally compr('ss{ld olecranon process. Distally the ulna narrows considerably
and articulates with the car_D.us.
(c) The wriSt or carpus.
The carpus is made up of eight bones. I n the
proximal row are three, the radiale and
intermedium articulating with the radius
and the ulnare articulating with the ulna.
The centrale is a small central bone wedged
between the two rows, thongh it appears to
belong to the distal row. The distal row
consists of four bones.
(d) The hand.
The hand consit;ts of five metacarpal bones
followed by five digits with typical numbE'l"'
of phalanges. Count the number of phalangeS in each digit and note.
Draw figures oj the arm and forearm with the wrist,
palm and dIgztS. Compare them with the (orresponding
bones in other animals.
THE RAT
3.
167
The Pelvic Girdle.
It is made up of two halves. Anteriorly they are firmly
attached to the sacrum and posteriorly they unite with
each other by means of a strip of cartilage at the symphyeis. Each half-the innominate bone-of the girdle is
made up of:
a. The ilium, a blade-like pOl:'tion running parallel to the vertebral column.
b. The acetabulum, a' concavity into which the
head of the thigh bone fit!!.
c. The ischium, the posterior and dorsal portion
of the innominate bone is the portion opposite
to the ilium.
d. The pubis, the smallest bone of the three
is a slightly transverse bone near the
acetabulum. The pubis, symphasis and
ischium enclose a cavity known as the
oblurator foramen.
Draw a figure oj halJ the pelvic girdle showing all the
parts and compare it with that oj the dog- fish, varantts and
pigeon.
4.
The Hind-Limb.
I.
A.
The
I
thi~h.
I
(i) The femur is the stoutE'st bone in th{' rabbit.
At its Janterior end it bears a rounded head
which :t:its into the acetabulum, and below
the head there are three projections: the
~reat trochanter, which is anterior most,
the lesser tr~chanter, which is opposite
16')
THE RAT
this, and the third trochanter, which is
just below the head. The diE>tdl end hears
two large condyles separated by a notch,
the intercondylar notclil, into which fits
the patella' or knee.cap. The condyles
articulate with the tibia.
(ii) The patella or knee cap iB a large bone connected by ligaments with the tibia and slides
in the groove on the front of the lower end
of the femur.
Feel your patella, move yoltr leg and see how it slides.
II.
The leg is made up of two bones of unequal Rizes.
(i) The tibia is a stout straight bone. Itfl enlarged proximal end bears two oval surfaces
on its upper end for the -articulation with
the condyles of the femur. Below the head is
the prominent cnemial crest, a ridge ruoning down the anterior surface of the bone.
DistalJy it articulates with the tarsal bones.
(ti) The fibula is a slender bone fused distally
with the tibia.
III. The tarsus consists of six bones arranged in two
rows with a central bone between them.
a. The proximal row of the tarsals consists of
two bones, the astragalus and the calcaneum. 'The astragalus lies on the inner or
preaxial side and articulates with the dil>tal
end of the tibia. The calca.DllUm is the largest
tarsal hone, along the ou·ter side of astraga·
Ius, and is produced into a large calcaneal
process or heel.
THE RAT
169
b. The central bone or centrale (naviculare)
is placed infront of the astragalus.
c. The distal row of tarsals consists of three
bones that support the foot.
IV. The foot has four toes only, each consisting of a
long metatarsal bone, followed by three phalanges, the
last of which bears a claw.
The first digit or hallux is rudimentary and represented by a backward1y directed processe at the proximal
-end of the second (apparent first) metatarsal, and articuJating with the central tarsal bone.
Draw figures and write notes on each important bone.
CHAPTEr.
VI
HISTOLOGY,
Having studied the gross anatomy of the organs it
becomes necessary to study the minute structure of the-'organs and the tissues of which they are composed.
Such a study is called histology or might equally well be
called miscroscopical anatomy Do you know what
is a tissues? The word is often used somewhat loosely.
In general it is applied to any aggregate of more or less
similar cells, together with any in1iercellllktr secretion
produced by them.
The study of histology is (lone either by "whole
mounts" i.e. taking bits of tissues and mounting them
as such, or by cutting sections and mounting them. The
whole mounts where only very small animals, or small
pieces of organs of larger animals are concerned are
studied in one of the following ways:
(A)
Saline mounts.
(i) The simplest form of fre8h cover-slip preparation is to take fresh tissne (or small animal)r
keep It in salt solution, put a cover-slip
and examine. Salt solution is used as it
keeps the tissues in fresh condition for a
long time.
(ii) There are certain dyes that can stain the
tissue:; in their living state. Neutral red
170
HISTOLOGY
171
i:; one of the commonest of such stains. It·
is dissolved in salt solution. Take thematerial, say connpctive tissue, spread it on
a slide and cover it with neutral red. Put a
cover slip and examino.
Methylene blue is Itlso used for staining fresh
and even living tissues. It is prepared in
clilute salt solution.
(B) Glycerine mounts. Material fresh or fixed is.
teased stained, mounted in glycerine and examined.
(C) Permanent mounts. PreparatIon of permanent
slides takes a sufficiently long time and needs great car~.
The following is the method of making permanent,
preparations:
(i) Fixation. Every fresh tissue, for such a study"
has to be killed in such a way that the protoplasmic
structures may remain, more or less, in the same condition
in which they exist in life. For this purpose the tissue is'
treated with such a reagent which kills it, penetrates
inside a,nd "fixes" its various contents. Such a reagent
is call'"ed a fixative and the process is called fixation.
INxatlOn, therefore, is a process of conversion of the more
or less soluble and diffusible substances constituting
protoplasm into insoluble and non-diffusible substances,
in such a way as to preserve the structures present in'
the living state.
(a) The fixatives. For the present purposes
the best fixatives and hardening reagents are;
1.
Absolute alcohol.
2.
Acetic acid glacial or its 5 per cent solution
which is specially used for rendering nuclei
more distinct.
_ft 72
HISTOLOGY
3.
Formalin ordinary 40 per cent which is very
helpful for gelatinous tissues.
(b) Procedure. Take the tissue on a slide or
in a watch glass and cover it with the fIxative
to be used. Leave for 10 to 15 minutes.
If the tissues are thick the time ma v be
increased upto half an hour.
.
Note: Formalin prrserved material, if given, need
not be treated by the above reagents as it is already
fixed.
(ii) Washing. After taking out the tissue f£om the
fixative wash it in water changing it twice or thrice, till
the fixative is thoroughly washed out. If the fixative
is not washed out completely the stain will not act
properly.
Important. The material is directly transferred from
water to stain, in case aqueous stains are to be used.
Sometimes the stains are alcoholic. In that case the
tissue has to be stained while it is being dehydrated.
(iii) Dehydration is a process with the help of which
water is removed from the tissues. To make a permanent;
preparation it is always necessary to remove water entirely
from the tissues. This is done by means of yarions
_grades of alcohols. In fact the real dehydrating agent is
.absolute alcohol, but if the material is put in the absolute
.alcohol directly from water the tissue gets distorted.
It is, therefore, treated with various lower :zrades
-of alcohols beginning usually from 50 per cent alcohol.
This is how it is done: Transfer the material from water,
whether it is after staining in aqueous stains or directly
after washing the fixative, to 50 per cent alcohol and
keep in it for at least .'5 minutes. 'Then transfer it to 70
per cent alcohol for.'5 minutes; from this to 90 per
HISTOLOGY
cent alcohol for 10 minutes. From 90 percent thematerial should be taken to absolute alcohol for 10-,
minutes. It is always better to change the absolute
alcohol twice.
So far as possible dehydration should be done in small
corked tubes.
(iv) Clearing. After removing moisture the material
has to be cleared. This process is called clearing which
is donl with the help of certain reagents called clearing
agents or clearatives. The best clearatives for the
present purposes are:
1. Xylol.
2.
Cedar-wood oil.
3.
Oil of cloves.
1Iethod: Add any of these to the absolute alcohol
containing the material. If the quantity of absolute
alcohol is enough drain off a little leaving only a small
amount in the tube and then add the clearing agent.
Atter a couple of minutes drain off the mixture and add
only the clearative. Leave the material in the clearative
tilI'it becomes transparent.
(v) Mounting: Now the material has to be transferred to some such 'medium that may penetrate the
tissue removing the clearing agent and at the same time
solidify. Thee are many such mounting media, as they
arc called, but the most suited for t,he present purposes
is canada balsam.
1-Iethod: Transfer the 'clear' material from the staining tube to a dry slide by means of a soft brush. Keep.
174
HISTOLOGY
the material in the middle of the slide. Cover it with a
,drop of canada balsam. Put the cover slip in such a
'Way that no air may get inside. This can be done
thus: Keep the coverslip perpendicularly on t.he slide
.beside the drop of balsam, support the free edge of the
.coverslip on a needle and lower it gradually till it covers
the matedal
(vi I Staining: To study the £iner structure of cells
in details It is better to colour the tissues.. The colouring
c!Jgents are of two types, those that stain the nucleus and
those that stain the cytoplasm only. ]ror the present
purpose the most popular 'nuclear' stains are carmine
.and haematoxylin, though they also give a general
colouration to the cytoplasm. Among the useful cytopJasmic stains are eosin and light green etc.
Often the material is stained in one stain only ana
.mounted; but sometimes, it has to be counter.;tained
with a cytoplasmic stain differing widely in colour from
the nuclear stain to be used first. For eXi~mple if haematosylin (blue) is used for the nucleus, eosin (red) may be
.used for the cytoplasm. Such a staining is called double
staining.
With respect to the solubility of the eolouring materials .the stains may be aqueous ie. dissolyed in water or
,alcoholic ie. dissolved in alcohols.
(a) Aqueous StaiRS.
Tf the aqueous stains have to be uspd tran~fer the
material into the stain directly after washing away th~
:fixative. Keep it for 10 to 15 minutes depending upon
the size of the materiaL Wash the stain in tap water
and examine. If the stain is more than needed differen-tiate the stain in acid wa.ter. Then dehydrate"
HI~TOLOGY
175
Gb) Alcoholic Stains.
If the stains to be used are alcoholic such as borax
carmine, which is dissolved in 70% alcohol then pass the
material from 50% stage to the stain giving it 10 to 15
minutes. If overstained differentiate it in acid alcohol
.and _upgrade.
Double staining; In case the material has to be
.stained with two stains say haematoxylin and eosin proceed as follows:
After washing off the fixative pass on the material in
haematoxylin. Keep it for 5 to 10 minute. Wash it in
tap water so the material becomes blue. Upgrade upto
70% stage. Pass it in eosin for i to 1 mts. Wash in
90% quickly and pass on to the absolute. Do not leave
in the absolute alcohol for long otherwise eosin will be
washed off. Clear the slide quickly and mount.
(vii) Differentiation: The superfluous stain has to
.be washed out if the material gets overstained. For this
purpose water with 1 % mtric or hydrochloric acid
is used for aqueous stains and 70% alcohol with same
percentage of acids as above is used at 70% stage for
,alcoholic stains.
To get good result it is always better
to overstain the material and differentiate. Differentiation does not only wash away superfluous etains but
jm proves the tone of the colour.
PREPARATION OF, TISSUES.
(a)
I.
Epithelial Tissue.
The Squamous Epithelium.
Gently scrape off the outer covering oj the skin oj a
preserved jrog alld examme it under a microscope. When
176
HISTOLOGY
a piece showing ,the characterist~c structure of squam~l(s
epithelium 1S obtamed dehydrate tt a)7er thoroughly washtng
the preservative in water. Stain the tissue in borax carmine
at 70% stage. Dlfferntiate in acid alcohol, upgrade, clear
and mount 1n canada balsam.
Peritoneum is other suitable material for the preparation of this type of epithdium.
(i) Note the cells are hexagonal with distinct
large nuclei.
(ii) Intercellular space is very much reduced.
II.
Columnar Epithelium.
Break up a shred of epitheliu:I1t from a minttie piece
of the mucous membrane oj small intestine of a joramlin
pseserved frog, and examine for columnar epithelium.
Dehydrate upto 70% alcohol, stain it in borax cramine
di iferentiate, upgrade and mOftnt in balsam. 1.{ake another
similar preparation and try double staining in haematoxylin
and eosin.
(i) The Cells are elongated rod-like lying side by side.
(ii) Nuclei are towards their inner Or deeper ends.
III.
Ciliated Epithelium.
(i) Gently scrap gff the m'lICOUS membrane of thepharyugeal region of the buecal cavity of a
recently chloroformed frog mount it in salt
solution and examine. The lashing movements
of the cilia can be seen.
177
HISTOLOGY
(ii) After thus isolating the cells fix them on the
slide in a week solution of formalin, for at least
10 minutes; wash the fixative well and up.
grade to 90 % alcohol. Now stain in borax
carmine for 5 mts. only, differentiate, up.
grade and mount. The whole process should
be completed on a slide.
(iii) Ciliated epithelium is also prepared from
a
trachea. Take a bit of trachea and treat it
with 1 % osmic acid for some hours. There·
after leave it in waler for at least a day or
two. The cells can easily be separated by
gently tapping the coverslip. Dehydrate and
mount.
(i) The cells are usually columnar.
(ii) At their free ends they bear extre.
mely fine tufts of cilia.
IV.
Glandular Epithelium.
(a) Simple Glands.
Examine a stained prepared section of the large intestine
following.
1)/ the rabbit and note the
(i) The glands are
surface.
simple depressions of the
(ii) The glandular epithelial cells lining the
pits or depressil!ns are short columnar.
granular cells, many of which are swollen
to form goblet cells.
12
178
HISTOLOGY
(b) Compound glands.
Examine a pre pared slide of the stomach of the frog alta
note the characteristics of a gastric gland.
(i) The cavity is not simple pit like depression
but subdivided or branched in a tubular
manner. Each branch is of tolerably uni.
form diameter.
.
(ii) Notice the neck of the gland and also the
mouth.
The liver and the pancreas are examples of rftCemose
glands. The description of these i~: given iIlt the next
chapter.
(B) Muscular Tissue.
(a) Striped Muscles.
Take a shred of muscle from a recently killed frog or rat
()n a dry slide and carefully tease the tissue along the length
of the bundles so as to separate single fibres. Stretch them
out and cover them with 4% acetic acid for 1tearly 15 minutes. Wash with water thoroughly and stain ill haematoxylin. Counter-stain in eosin at 90 % stage, dehydrate,
clear and mount.
Examine and note :
(i) The transverse striations.
(ii) The spindle-shaped lauclei scattered here
and there.
(iii) The sarcolemma-delicate elastic sheath. ,
179
HISTOLOGY
(b) Unstriped Muscles.
Vnstnped muscle fibres can be mounted exactly in the
-same way as the striped. The material should be taken
fr01It the ttrinary bladder of a frog or jrom the In Itscular wall
of the mtestines.
Examine and note :
(i) The hands of muscular fibres.
(ii) A number of fusiform, nucleated
cells forming the hands
muscle
(iii) The cells are not striated.
~C)
The Connective Tissues.
(1) The Blood.
There are many methods of studying the blood. Of
these only two given below, will be quite helpful for the
:present purposes.
(a) Obtain a drop oj frog's blood on a dry slide altd
mix it with a drop oj salt solution {tpon
the slide. Examine with a high power.
(i) Notice t,he shape of the coloured torpuscles
both when seen fiat and sideways.
(ii) Notice the colourless corpuscles, smaller than
the red corpuscles and pall;' in· colour. Do
not confuse them with the rounded liberated
nuclei of crushed red corpuscles.
~iii)
Also try to make out
blood pIa.telcts.
the spindle-shaped
180
HISTOLOGY
~b) Make a thin film of blood on a dry slide and dry it
quickly in air. Fix the film by immersing for aboztt 30 mts.
in a tube containing 90 parts of absolute alcohol and 10 pa~ts.
of formal, or by simply pottring absolttte at~oltol on the sh~e
and keeping tt for 20 to 30 mts. Stam w haemutoxyltrt
first and upgrade. Counter-stain· in eosin after 70% alcohol.
stage. Qttickly ttpgrade and moullt in canada balsam.
Important. To make a film take two dry slides. Keep
a drop of blood on a slide. Keep tlte ground edge of the
other slide just in umtact with the drop and then keeping tt'
almost perpendicular quickly draw the shde evenly over the
surface oj the other slide. This will leave a thin film of
blood on the slide. If the film 1S not thin or even try it again.
Make preparations of the blood of the bird, the varanUB
and the rat and examine similarly. Note the salient rlointB
of differences between the blood of these animals.
In case a preparation of human blood has to be made
prick the finger above the nail or the tip wront. Be
careful to sterilize the needle in flame before pricking.
Proceed further as usual.
(2) Areolar Tissue.
(a) Take a bit of the subcutaneous tissue and spread it out
into a large thin film with needles on a dry slide. Keep the
centre moi~t by occasionaUy breathing on it, but allow the
edges to dry on the slide. Put a droj) ·of salt solution on a
glass cover-slip and now iuvert this over the film. Examine:
with a high power and sketch.
Note (i) Wavy bundles of whit,e fibres.
(ii) Straight, slender yellow elastic fibres ..
(iii) The connective tissue eorpuscles-.
HISTOLOGY
lSI
(b) To make a permanent prepar.ation make another film
-of the subcutaneous tissue as directed above and fix it by pouring 10% formal and keeping in it for about 20 mts. Wash
in water and stain in haematoxylin. Counter-stain in eosin.
ilehydrata and mount in balsam. Examine and sketch.
(3)
Cartilage.
Cut two or three thilt sections of a fresh cartilage of a
joint or of epi-or xiphi·sternwlt of the frog. Mount ilt
salt solution and examine. Make some more sections and
treat them with 1% acetic acid for 10 mts. wash well with
water and stain with haematoxylin. llfolmt in glycerine.
Perm:ment slides of this can be made by the usual methods
bitt as the sections are relatively thicker it 1S no use making
a permanent slide. Only mount in glycerine, examine
.and sketch.
Note
(i) The intercellular matrix.
(ii) The cartilage cells embedded in the matrix
in definite cell spaces. Dividing cells are
also seen.
(4)
Bone.
For the study of bone examine prepared slides showing
;the structure of ta.) simple bone (b) compound bone.
(a) Simple bone.
(i) The outer osteoblast cells.
(ii) The bony lamellae surrounding the marrow
cavity.
(iii) The lacunae
01'
cell spaces.
(iv) The canaliculi or the fine branching canals
connecting the lacunae.
182
HISTOLOGY
(v) The inner osteoblast layer.
(vi) The marrow cavity.
·tr1.b) Compound bone.
~ - -:..r::~~
1\
,._J,.,. tt
(i) The Haversian~systems form the greater
part of the bone, and are readily recognised
by the concentric arrangement of the lamellae'
round the central callaIs, the Haversian
canals.
(ii) The lacunae or cell spaces cover the lamelllj,e as usual.
(iii) The canaliculi.
(iv) The marrow or the m'ldullary cavitT is as
'usual in the centre.
(v) The circumferential lamellae are a series
of concentric lamellae parallel to the surface
of the bone, and forming its most superfecial layer.
(vi) The prepledullary lamellae are a series of
concentric l'amellae lining the central medul·
lary'cavity of the bone.
Also examine a longitudinal section of a long bone.
(D)
Nervous Tissue.
(a) Nerve Fibres.
Take a piece of a big nerve, say the vagzts, stretclt it fltlly
witlt two needles and keep it in 1 % osmic aCid for 24 hOltrs.
After washmg in water separate a small piece of nerve into
HISTOLOGY
183
its fibres keeping in a dilttte solution of glycerine. Mount
in glycerine and examine under low and high powers and
see if yOlt can locate.
(i) The medullary sheath.
(ii) The nodes of Ranvier,
(iii) The nuclei of neurolemma etc.
(b) Nerve Cell.
Put a small fragment of spinal ganglion of the frog into
1 % osmic acid for a few hours, place it in water containing
a fragment of thymol for two days or more. Tease in dilute
glycerine and examine the strllctttre of a nerve cell or
neuron.
(i) Eac'j neuron consists of a cell-body from
which arises a system of branching processes.
(ii; Tho dendrons and their subsequent branches,
the dendrites, are small branches.
(iii) The axon is a long branch of each neuron
that passes into a nerve fibre.
CHAPTER
VII
HISTOLOGY (CONTINUED).
For the study of the histology of various organs prepared slides will be provided. Stndy them in comparative manner and note down the salient features of differences between the histology of organs of the different
classes of animals.
1. Skin.
Examine a vertical section of mammalian skin,-skin of
the rat, rabbit or man and note the following feattlres ;
(A) The epidermis, the outer layer made up of
(i) The outer stratum corneum in which the
cells are arranged in stratified layers.
(ii) The innermost malpil~hian layer, a layer
of columnar cell'l. D_o you know the function of this layer ?
(B) The dermis or corium is the deeper layer made
up of a net-work of connective tissue having both elastic
and non-elastice fibres. Some fibres lie horizontally while
others are perpendicular to the surface. This layer is
richly supplied with blood vessels, therefore, numerous
blood vessels cut in longitudinal or transverse sections are
seen. Cutaneous glands, seb!tceous glands and roots of
hairs, derived from the epidermis, become embedded
184
HISTOLOGY'
185
in the corium. Fat cells in the lower layers are numerous.
Skin muscles are few. Where do you find them ?
(Jompare the skin of mammals with that of the frog.
Also examine the skin of fishes, reptiles and birds and
note the differences.
(a) Skin of Fishes is scaly.
(i) Epidermi::o is highly glandular, not differentiated
into corneal and Malpighian layers.
(ii) Dermis or corium is a typical mesh-work of connedive tissue more stratified in its deeper parts and bearing
the embedded scales which it gives rise. How do the
.dermal scales of fishes differ from those of the reptiles?
(b) Skin of Birds.
Epidermis reduced to a delicate thinness, the corneal
Jayer Qf epidermis is thickened only in those parts
not covered by feathers like the shank etc. Feathers,
beak, leg-scales are only epidermal.
Dermis also reduced much.
2.
Structure of Tooth.
Examine a longitudinal section of tooth of mammal.
The tooth consists of three parts externally.
(a) The crown is the outer enamel capped portion.
(b) The root is the end portion buried in a bony
,socket or alv~olus.
186
HISTOLOGY
(c) The neck is a constricted region between the root
and the crown.
Internally each consists of :
(i) 'The pulp cavity is a longitudinal centrltl
canal, opening at the end of the root.
(ii) The dentine is the bone-like substance that
forms the large mass of the tooth. It sur-
rounds the pulp cavity. At no place on the
tooth does the dentine reach the surface
since the crown or neck are covered with
enamel while the root, is surrounded by a
heavy cement.
3.
The Stomach.
Examine a transverse section of the stomach of the rat or
rabbit and note the following parts.
(i) The serous coat derived from the peritoneum.
(ii) The muscular coat consisting of two layers
of muscle fibres.
(a) The longitudinal or outer layer in which
the bundles run longitudinally. (In the frog
this layer is replaced by connective tissue
layer called subserosa).
(b) The circular or inner layer which consists of
muscle fibres disposed of circularly.
(iii) Th~' submucosa consisting of areolar connective tissue and having a number of
branches of blood vessels.
HISTOLOGY
187
(iv) The mucosa in which is embedded the
glandular tissue--the gastric glands mainly.
muscularis mucosae is a thin double
layer, composed of circular muscles (inner)
aJld longitudinal muscles (outer), in between
the mucous coat and the submucosa.
(v) The
Examine the gastric glands under high power and sketch.
A gastric gland is a tubular gland consisting of one
to five secreting tubules t.hat form the body of the gland.
The tubules opE'n into a narrow neck which opens into the
lumen of the gut through the mouth.
4.
The intestine.
Examine a T. S. of the intestine of the rat. Also exa·
mi 11 C T. S. through duodenum of tl e rat and ilium of the
cat. Note the following parts:
1.
The outer serous coat of peritoneum.
2. The next muscular coat of longitudinal and
circular muscle fibres.
3.
The submucosa consisting of areolar tissue.
4. The mucosa having
epithelium.
simple layer of glandular
In the region of the duodenum and near it the following
other structures are also met with.
(i) The crypts of Lieberkuhn arc simple tubular
glands lined throughout by columnar epi.
thelium with scattered goblet cells, and
lying between adjacent villi.
3188
HISTOLOGY
~ii)
The Brunner's gland are small tubulo-mcemost> glands situated in the submucosa. They
open into the lumen of the gut t>ither
between the crypts of Lieberkuhn or into
them.
I
(iii) The Peyer's patches. The mucous membrane betwr.en the glands is mainly composed
of reticular tissue, which contains nodules
of lymphoid tissue, here and there. When
they occur singly the nodules constitute
so-called solitary glands of intestine, but
when aggregated together they ·form the
patches of Peyt'r. The Peyer's patches are
chiefly formed in the ilium.
5. The liver.
Study sections throltgh the live:r of the rat, pig and
other mammals, note the following fecrtures aud sketch.
The liver is a solid glandular organ made up of hepatic
lobules separated from one an~ther by connective tissue.
In some animals such as the pig this separation is complete, but in other animals such as the rat or the rabbit
it is incomplete.
(iJ The hepatic cells. Each lobule consists of
a mass of polyhedral cells pierced <:lvery
where with a network of blood vessels. Cells
are granular in appearance a nd contain a
spherical nuclei.
(ii) The interlobular bran<:hes of blood vessels
are found between the lobules ie. they are
at the periphery of lobules.
(iii) The intralobular
veins are
centre of the lobules.
found in the
HISTOLOGY
189·
(iv) Tho hepatic ducts.
The smallest ducts commence between the hepatic cells in the form
of intercellular bile-channels, which lie
b{'tween the adjacent sides of the cells and
receive the secretions of the hepatic cells._
At the periphery of the lobules the intercellular channels pass into interlobular
bile-ducts, which formally form the biIeduct proper. The bile-ducts are lined bycolumnar epithelium, outside which is a
basement-membrane. In larger ducts some
fibrous and plain muscular tissue may alsobe noted. Knowing this can you distinguish
a section ofa bile duct with that of a blood'
vessel ?
(v) The Glisson's capsule is a capsule of loose
connective tissue enclosing the branches of
the portal vein, the hepatic artery and the
bile-duct and also the lymphatic capsules.
In transverse section such capsules appear as
circular or oblong spaces enclosing smallm
circles representing the various types of
vessels.
6.
The Pancreas.
The pancreas is a racemose gland with longer and
tubular alveloli. The connective tissue between the alveoli
is somewhat looser.
Examine a T. S. of the pancreas of the rabbit or man
and note the following characteristics.
(i) The pancreatic cells lining the alveoli are
polyhedral in shape with granular cytoplasm.
(ii) The acini (singular acinu8~ of the pancreas·
are reduced and often occupied by spindle-
190
HISTOLOGY
shaped central cells,
hollow.
instead of being
,(iii) The islets of Langerhans are clusters of lightly
staining cells. The area of these clusters
in section is considerably greater than that
of a single acinus. The islets are ductless
glands of the pancreas that secrete insulin .
.7.
The Kidney.
A. Cllt a ktdney of the goat or sheep (or even the rat
.if big szzed kidney is not '!vailab.e) lengthwise into two
Aalves and examine.
To the naked eye it appears to be formed of two
Jlortions.
(i) The cortex or the outer region which has a
contorted arrangement of the uriniferous
tubules •
.(ii) The medulla or the inner region in which the
tubules have a straight course .
•(a) The pyramid is a cone-shaped l:Itructure the
base of which rests against the cortical layer
while the apex, the papilla projects into
the cavity of the pelvis.
~b)
The pelvis is the dilated commencement of the
ureter.
B. Study the sectwns of a mammalian kidney
under low and high
following:
powers and
110te
the
1. The cortex shows a number of rounded structures scattered here and there. These are
HISTOLOGY
191
different-sized sections of the Malpighian
bodies passing through their various aspects.
Along with these longitudinal as well as
transverse sections of convoluted uriniferous
tubules are also seen.
{i) The Malpighian body is the dilated commencement of the uriniterous tubule hollowed
out at the tip; and containing the glomerulus in it.
\(a) The Bowman's capsule is the mme given to
. the hollowed out commencement of the
uriniferous tubule.
,(b) The glomerulus is a lobulated knot of blood
vessels lodged into the Bowman's capsule.
Ui) The neck is the narrower portion of the tubule
immediately below the capsule. (The neck
is very prominent in the frog and not so in
mammals.)
(iii) The body of the tubule is the remaining portion. The tubule leaves the capsule by the
neck and is convoluted in the cortex,
then it becomes nearly straight and passes
down into the medulla towarqs the pelvis.
II. The medulla presents section through a
-number of uriniferous tubules lying parallel to each other.
III. The blood vessels are seen cut transversely as
'well as longitudinally all over the surface of the kidney.
8.
The Testis
Examine a T. S. of the testis of the rat or the rab'Jit
a.mder low power and note the following structures:
192
HISTOLOGY
(i) The tunica albuginea is the outermost'
fibrous capsule.
(ii) The crypts are the circular oval, and
sometimes elongate surfaces representing'
the transverse sections through the seminiferous ~ubules. 'The glandular substance of
the testes is wholly made up of convoluted
tubules, the seminiferous tubules. In
transverse sections only their cut ends are
visible.
,
Examine a crypt fInder high power.
(a) The germinal epithelial cells form the outer
margin of the crypts.
(b) The spermatogonia, the
speunatocytes·
and the spermatids are found in the successive internal layers ; of these the spermatids.
have very prominent nuclei occupying almost
entire cytoplasm.
(c) The spermatozoa are found in groups or
bundles in the lumen of the crypt; and they\
can be easily recognised by their tails and.
elongated heads mainly occupied by elon-·
gate nuclei.
(d) The Sertoli cells are elongate cells found
here and there among the germinal epithelial cells of the ou1jermost layer of the crypt.,
They conduct nourishment to the interior.
(iii) 'The interstitial cells are spindle-shaped'
cells embedded in the connective tissuefilling up the spaces between the adjacent
tissues.
193
HISTOLOGY
Compare the structure of the transverse section of
the testis of a. illammal with that of the frog and the
pigeon.
9.
The Ovary
Study the transverse section of the ovary of tlte rat or
the rabbit both under low and high powers.
(i) The germinal epithelium is the outermost
layer of the ovary.
(ii) The stroma is the fibrous tissue forming
the main bulk of the ovary. Scattered all
over the stroma can be seen sections of
blood vessels
(iii) The ova of different sizes in the various
stages of development can be found through.
out the stroma. The smallest of these, the •
oogonia, are found near the outer surface,
the larger ones, the primary oocytes, the
secondary oocytes, the primary follicles
and the Graafian follicles etc. are placed
more deeply in the stroma, although as the
Graafian follicles incren.se in size they
extend towards the surface.
(1) The primary follicle. In the early stages
the primary oocytes are not surrounded
by the epithelium of follicle cells. In the
smallest follicle the epithelium is formed
of a singl!.'- layer of cells. In still larger
follicles the epithelial cells are in two layers
and are more or less columnar in shape.
In still further stages each of the two layers
becomes several cells deep and in between
them fluid begins to collect at one place.
This liquid is the liquor folliculi.
13
194
HISTOLOGY
(2) The Graafian follicle.
Examine a Graafian follicle under high power.
(a) The theca externa and the theca interna
are two layers forming the wall proper of
the Graafian follicle. These layers are derived from the stroma.
{b) The membrana granulosa is the outer layer
of follicle cells often formed of several strata
of cells.
-( c) The cumulus oophorus or discus proHgerus
is the mass of follicle cells which surround
the ovum.
{d) The liquor folliculi is 3. liquid filled' space in
the follicle cells bound by the membrana
granulosa externally with the discus proligerus on one side.
()RAPTER
VIII
THE DEVELOPMENT OF THE CHICK.
'rhe requirements for the practical work on embryo~
'ogy for the standard for which this book is meant are
iimited. As such the following account consists of mere
'explanatory note:> to explain the characteristic features of
certain important stages in the development of the chick
.so tha.t the student may find it easy to study them.
1.
The Egg.
The egg of the fowl
is large-yolked i.e. telolecithal. In other word
the cytoplasm of the egg
ill charged with yolk
(deutoplasm),
which
serves as a source of
nourishment
for the
Fig. 17.-The egg ofa hen with young organism until
half of the shell removed. it can feed for its'Jlf.
,:\he yolk is, as a rule, aggregated chiefly towa,rds one
pole of the cell, the vegetative pole, whilst the egg nucleus
lies near the other pole, the animal pole. The egg of the
fowl is surrounded by tertiary membrane (the shell)
deposited around th'3 egg during its passage down the
,oviduct.
SH~(,,~ .... ~~
1otE.r.leRArfE~
'VITE:lLtNE
MtMeR~N£
Remove half of the shell of a hen's egg carefully and
,examine the internal structures.
195
EMBRYOLOGY
196
(i) The blastodisc or ~~erminat disc is a smaH
area of cytoplasm forming a cap at theanimal pole. This is completely surrounded
by yolk. In the centre of the blastodiso
lies the germinal vesicle (egg nucleus).
(ii) The yolk consists of a central mass of yellow
yolk. A careful examination reveals that
the yellow yolk is not of uniform composition. It consists of a central mass of whitish
yolk around which are arranged alternating
concentric layers of yellow and white yolk
(not to be confused with the" white of an
egg ").
(iii) The vitelline membrane is the transparent
membrane investing the oocyte.
The "white of egg" gets deposited around
the egg during its passage down the oviduct.
Because oHhe rotating movements of the
egg the "white of egg" gets deposited in a
spiral fashion which is most clearly shown
by twisted cords of albumen, chalazae, at
each end of the egg. The "white of egg'"
is secreted by the glandular walls of r,he
upper parts of tue oviducts, whereas, the
lower part secretes watery albumen and the
material forming the outer tough shell
membranes.
The calcareous shell is
secreted by still lower portion of the
oviducts.
2. Fertilisation. The ovum is fertilized in the upper
part of tho oviduct before the deposition of'the albnmen
around it. Therefore, the hen's egg, when laid, is a
zygote, a double structure composed of both malo anci
female nucleus and protoplasm.
EMBRYOLOGY
197
3. Cleavage. This is the process by which the
'Zygote divides into many cells or blastomeres which
become smaller and smaller as cleavage progresses The
process of cleavage is said to end with the completion
of the embryonic stage termed blastula, though the
division continues throughout life. As the egg is heavily
yolked, cleavage is ('onfined to the blastodisc only. Such
cleavage is of the meroblastic type. Cleavage begins soon
.after fertilisation and continues till the egg passes down.
Examine prepared slides showing various- important
phases vf the. development of the chick and sketch.
(i) The blastoderm is the name given to the
blastodisc after cleavage has started. After
a couple of divisIOns the cells of the blastoderm become completely delimited.
A
vertical section of the blastoderm reveals a.
row of more or less rectanguhr cells just
above the yolk cells.
Fig.
18 -Median
section of chick blastoderm showing
segmentation cavity
(ii) The blastocoel is the subgerminal cavity
formed below the central cells of the
blastodisc. The marginal cells remain as a
layer directly living on the yolk. The
embryo is now in the blastula stage.
(iii) The extra-embry,onic endoderm. Further
horizontal cleavages make the blastoderm
198
EMBRYOLOGY
I
several cell-layers thick. The blastoderm
becomes larger spreading over the yolk
which is engulfed and digested by the
marginal cells as they encroach upon it. The
marginal cells are several layers deep, except,
at the extreme periphery. This layer lies
directly on the top ot the yolk and is known
as the yolky endoderm which later on
forms the extra-embryonic endoderm.
Examine a slide presenting the surface view of the
blastoderm.
(iv) 4t this stage the blastoderm shows two distinct areas. A centrally situated relatively
clear area, the area pellucida, lyhg just.
over the subgerminaJ cavity; and a darker
zone surrounding it, the area opaca.
Fig. 19-Yertical section of blastoderm showing formation of the endoderm
4. Gastrulation. In gastrulation a re-arrangement of
the cells of the blastula takes place. In the chick gastrulation is separable into three distinct phases, namely, the
laying down of th~ embryonic endodt'rm, mesoderm
formation and the formation of the embryonic axial
structures.
(i) Endoderm Formation.
Examine a medwn longitudinal sc'ction of the blastoderm
showzng formation of the endoderm.
EM:BRYOLOGY
199
As gastrulation begins the blastoderm expands and
the cells of the area pellucida become re-arranged to form
a single layer of cubical cells in the form of a definite
epithelium_ The cells from this layer migrate onwards
at the posterior end of the blastoderm and form a complete floor of the subgerminal cavity. This layer is the
embryonic endoderm
Thus a two layered embryo is
formed, ~he outer layer the ectoderm and the inner
endoderm.
(ii) The Primitive Streak.
(a) Examine a whole mount of blastoderm showing
the prtmitive streak.
--./'
'·:lios~.
Fig. 20-Surface view of the blastoderm showing the
primitive streak and the forlJlation of the notochordal process
The primitive streak is a linear groQve flanked on either side by ridge-like thickenings
extending from the inner margin of the area
opaca to approximately the centre of the
200
EMBRYOLOGY
blastoderm. The primitive streak marks
the longitudinal axis of the future embryo.
The end adjacent to the area opaca is posterior whereas the other is anterior. At the
anterior end the streak has a distinct IjIwelling, the primitive knot &r Hensen's node.
(b) Examine a median lon~i'tudinal section of the
blastoderm showing thl~ e'J.rly appearance of
the primitive streak.
In its early stage the primitive streak is just a
thickening of the blastoderm. In section
therefore it appears as a thickened area. of
ectoderm. cells.
(c) Examine a median longitudinal section of the
blastoderm showing the appearance of the
primitive groove.
Fig. 21-1'ransverse section of the embryo showing
the migration of mesoderm.
The primitive groove is a narrow groove developing later on the surface of the primitive
streak In section this appears as a shallow depression.
(iii) Mesoderm Formation.
Examine a median longitudinal section through primitive streak of at last 15 hour embryo.
EMBRYOLOGY
201
As the primitive groove becomes fully formed there
is, at this iime, a complete fusion of ectoderm and endoderm in the region of the primitive streak. From either
side of the streak bud off certain cells and migrate side
ways. TheRe are, the primitive mesoderm cells. They
congregate, form a mass on either side and are further
drawn into definite mesoderm sheets.
(,iv) The Notochordal Process.
Examine a slide showing the formaliOJ1 of the notochordal
process.
The notochordal process.
The cells of
the primitive knot migrate in a forward
direction so as to form a column of cells
connected behind with the primitive knot
and lying in the middle line.
(v)
Neural Tube Formation.
(a) Examine a slide showing the formation
the neural plate.
of
The neural plate is formed in the early
development stages by the convergence of
the cells of the area pellucid a in the anteroposterior direction to finally occupy the
longitudinal axis of the body just above the
notochordal process.
The neural plate
extends from the anterior eni of the embryo
to the posterior end of the primitive streak.
As it becomes longer the primitive streak
diminishes in size and ultimately disappears
(this happens at about 40 hours incubation).
(b) Examine preparations to show the neural folds
both in surface view and in sections.
202
EMBRYOLOGY
Soon after the formation of the head fold the
lateral margins of the medullary (neural)
plate are elevated to iOlLm the neural folds
between which appears a deep groove the
neural groove. These folds as they increase.
in size bend inwards, toward each other, and
meet in the midline Dorming a tube, the
neural tube.
:Fig. 22-Surface view of lO-somite embryo.
(c) Examine more preparations to study the for-
mahan oj the nemal ttebe and its primary
dimsions.
The anterior end of the neural tube become:;·
enlarged and rapidly differentiates i~to three
regions separated by constrictions. (1)
EMBRYOLOGY
203'
The anterior divison is the forebrain that
expands laterally into the optic vesicles;
(2) the middle one is the midbrain and (3)
the hindbrain plainly marked by constrictions into a number of neuromeres.
(vi)
~ead
Folds.
(/,t) Examine an entire mount showing the forma-
tion of the head fold.
Fig. 23-Lollgitudinal section of a young embryo
showing the head fold.
The head fold appears as a wide transverse
crescentic fold across tho area pellucida just
infront of thc head process, where the
blastoderm consists of only two genu layers
ectoderm and endoderm. The head process
is the forward growth of the primitive ~tren,k
which appears ill front of the primitive knot
after about 18 hour's incubation and is the
forerunner of notochord. The appearancc
of the head fold marks the first step
in the separation of the embryo from the
blastoderm.
(b) Examine a longitttdillal section
formatiolt of the head fold.
illustrating the
:204
EMBRYOLOGY
The formation of the hell,d fold raises the
curved anterior end of t,he medullary plate
and as the fold moves b!wk under the head
a pocket lined with endoderm is formed
beneath the medullary plate. This is the
primordium of the foregut.
(vii) Paraxial mesoderm.
Examine entire mounts as well as sections showing somitcs.
ID'ig. 24-Surface view of the embryo showing head fold
and formation of two somites"
205
EMBRYOLOGY
Ali the early head fold stage the lateral wings
of mesoderm spread from the sides of the
notochord and laterally across the area
pellucida. The thickened inner margin of
eactl wing, the paraxial mesoderm, forms
a distinct band of cells bordering the noto.
chord on either side, whereas, the outlying
mesodermal sheet forms the lateral plate.
The paraxial mesoderm becomes segmented
by transverse grooves leading to the for.·
mation of somites.
Fig. 25-Transverse section of the lO·somite embryo
showing the formation of splanchnocoel.
Fate of somites. A somite when first formed
is a block of cells. Each somite givcs rise
to three structures.
(i) The
sclerotome which later develops into
vertebrae and connective tissue.
(ii) The dermatome which is transformed into
the dermal layer of the skin.
(iii) The myotome
muscles.
develops
into
voluntary
(viii) Lateral plate.
Examine a transverse section of the embryo showing the
formation of the amniocardiac vesicles or pericardial cavity.
20()
EMBRYOLOGY
The lateral plate of mesoderm splits into a
somatic layer above and a splanchnic
layer below enclosing a cavity, the amniocardiac vesicle, in between.
This occurs at about six-somite ·stage. The
somatic layer of mesoderm and the adjacent
ectoderm, with which it Boon forms a close
contact, constitute the somatopleure th'J
splanchnic layer with the endoderm form
the splanchnopleure. The space between
these two layers is common to the cavities
of the pericardium and the extra-embryonic
coelom. The simultaneous formation of
small spaces in different parts of the lateral
plates and thcir subsequent connection with
one another and with the amniocardiac
cavity results in the formation of a s;ngle
large cavity, the coelom, bounded above by
the somatopleure and below by the splanchnopleure. Later this single cavity may be
divided into embryonic coelom and extraembryonic coelom.
(ix) The Gut , Formation.
Fig. 26-Transverse section through a seven-sorr ite
embryo showing the formation of fore-gut.
Examine a transverse section of all embryo of six to
-seven somites.
EMBRYOLOGY
207
Fr\Jm the above it is apparent that two inwardly
.directed folds arise from the right and left sheets of
splanchnopleure and advance towards each other. These
lateral folds finally meet and fuse below the embryo so at
first side walls, and later, the ventral wall of the fore gut
are established. The fore gut continually increases in
length as the fusion of right and left sheets of splanchonpleure progresses.
(x) The Heart Formation.
o
Fig. 27-Transverse section of the embryo showing
the formation of the heart.
Examine transverse f'ection of the 7 -somite and lO-somite
embryos to study the formation of cardiac tube.
J n the region of the hind-bra.in, as tlie amniocardiac
vesicles approach each other in the midline below the
pharynx there appears a large blood vessel, the rudiment
of endocardium, on each side. Both these later fuse to
form a single tube, the cardiac tube, below the pharynx.
The inner wall of the amnio-cardiac vesicles which lie
against the endocardium form the muscular wall of the
heart and are known as the myocardium.
(xi) The Amniochorionic Folds.
208
EMBRYOLOGY
Examine preparations shJwing the head folds' of the
amnion.
The amnion and chorion arise as folds of the ectoderm of the blastoderm on either side of the midline.
Each of these folds is called the head foldl of the amnion.
Each begins to grow rapidly over the head of the embryo
to form a complete arch. Finally they fuse fmd leave
two layers-the outer having ectoderm outermost and
mesoderm innermost is the chorion, whereas, the inner
layer having its ectoderm next to the embryo and its
mesoderm outside is the amnion.
(xii) The Allantois.
Examine a sli~e of a 28-somite stage of the embryo
the study of allantois.
fO?
Soon after the hind gut ha~ been formed by the tail
fold of the embryo the ventral wall of the hind gut, jURt
infront of the anal plate, grows out t,o form a sort of
bud which projects out into the coelom. This is the
allantois. It grows in size rapidly and becomes a pearshaped vesicle lying between the amnion and chQrion.
Later the mesodermal layer of the allantois fuses with
that of the chorion forming, the allanto-j~horion.
Further examine sections of the various stages of embryo
passing through the heart, the kidneys, lhe lungs and the
limbs etc.
CHAPTER
IX
MAIN GROUPS OF VERTEBRATES
The classification of the animals is merely a convenient
filing device in which each organism is place::l in a particular position in accordance with its resemblances and
differences (phylogenetic relationships) with others.
Accordingly the vertebrates are divided in five classes
that will be des ribed in the following pages.
CI.. ASS PISOES
,
Class pisces is divided into five sl1b-classes.
Sub-Class l.
"
"
"
Marsipobranchii (Cyclostomata.}
2. Elasmobranchii.
3. Ganoidei.
4. Teleostei..
5.
Dipnoi (Lung Fishes.)
Sub-class Marsipobranchii.- Vermiform animals
with smooth scaleless, slimy skin ; suctorial mouth
devoid of jaws; piston-like tongue with horny epidermal
teeth; vertebral column unsegmented; notochord carti-
209
14
210
CLASSIFICATION
laginous and p~rsistent ; single median nasal organ;
intestine straight; segmentally arranged mesonephros ;
one or two semi-circular canals in the ear; without paired
appendages, generative ducts and conus a.rteriosus ;
caudal fin practically diphycercal.
~mily Petromyzontidae.-Lampreys with seven pairs
of external gill apertures leading into a subpharyngeal tube. Branchial basket present; mouth surrounded
by circular lip and is provided with yellow horny teeth;
nasal organ in the middle of the dorsal side of the head
and the nasal duct ends blindly. Eyes present. Two
dorsal fins. Intestine with spiral valve; gall. bladder absent.
Found in the frest-waters and coasts of the temperate
regions of both hemispheres.
~¥mple Petromyzon.o",
L()..V"'-\,A,\ .
vffamily Myxinidae.-Hagfishes with six p'lirs of
branchial sacs opening by a pair of external apertures
and leading directly into the pharynx; branchial basket;
mouth without lips, but sourrounded by barbels; nasal
aperture at the anterior end of the body and the nasal
duct opens into the pharynx; eyes very imperfeot and
hidden under the skin; dorsal fins and intestinal spiral
valve absent but a gall.bladder is present; <:set'ies of segmentally arranged mucous-glands present on either side of
the body. Attach themselves to living fishes and gradually
bore their way into the coelom, devouring the flesh as they
do so. Marine, found in temperate regions of both hemispheres.
~ample
Myxine.
Sub·class Elasmobranchii.-Sharks, rays and, chimaeras. Fishes with a cartilaginous el'ldoskeleton, placoid
scales cover the body; and abdominal pelvic fins provided
CLASSIFIOATIO N
2.J.l
with claspers in the ma.le. The externa.l opening of the
doaca serves as a common outlet for the rectum as weH as
the rena.l and reproductive ducts. Operculum is absent
except in the holocephali and the gills are la.minar. There
is a conus arteriosus, an optic chiasma and a spiral valve
in,bhe intestine. The oro-nasal groove, the pericardioperitonial canal and the large sinuses in the venous
system are the characteristic features of the sub-class.
The eggs are large and provided with a horny case. There
is no air-bladder. With very few exceptions exclusively
marine.
Order 1.
"
"
"
"
Pleuropterygii (extinct)
2. Acanthodi
"
3. Ichthyotomi
"
4. Holocephali
5. Selachii
Suo-order 1.
2.
Notidani.
Squali.
3. Raji.
-Drder Holocephali.-Unique; with four gill. clefts
covered over by an operculum; adult with naked skin;
spiracle absent; skull autostylic; eyes large and high up
on the head; mouth small, ventral and bounded by
lip-like folcls; three pairs of teeth in the form of tritural
plates ; nostrils confluent with the mou'th; anterior
dorsal fin has a strong spine on its front border; tail
prolonged in chimaera into a long filament; extra claspers
on the head and is front of the normal abdominal pore;
212
CLASSIFICATION
notochord unsegmented and with numerous calcified
rings; urino-genital part of the cloaca, is separate from
the rectum. Found on the coasts of Europe, Japan,
Australia, West coast of North America and the Oape of
Good Hope.
~ample
Chimaera.
OnJer Selachii.
Sub-order Squali.-Shark..!h.. with five gill apertures
laterally 'placed, spiracle present or absent, never large ~
with two dorsal fins and with or without anal fins .
./""Family Scyllidae.-Stegostoma-,!:_iger-shark.
With
/alternating briUiant dark-brown and white bands )ver
the body and fins. Attains a length of fifteen feet. Inhabits Indian Seas..
/ . Family Carcharildae.-Zygaena-Ham mer-headed shark.
Head transversely expanded with ey;~s at the extremity
of the head lobes; mouth ventral and crescentic ; spiracl~
absent; viviparous. Temperate and Tropical Seas.
F amity Cestraciontidae-Bull-head sharks
"
"
Lamnidae-Mackerel sharks
RlmlOdontidae-Whale-sharks
Rhinidae-Ray-like sharks
Pristiophortdae-Shark
"
"
Scymnidae
Spinacidae
~~
CLASSIFICATION
213
Sub-order RajL-Skates and rays_ Body flattened
dorso-ventrally; pectoral fins enormously expanded anteroposteriorly; gill openings ventral, five in number;
spiracles rpresent and dorsally placed behind the eyes;
.caudal region usually slender; dorsal fins, if present, on
.the tail; without anal fin.
Family Pristidae.
ample Pristis.-Saw-fish. Snout produced into a
process of cramum and provided with lateral
saw-like teeth; body disc-like and gradually passing into
the comparatively thick tail. Tropical and sub-tropical.
Family Rhi1tobatidae.
Example Rhinobatus.-Guitar-fish. Tail long strong
and without serrated caudal spine; rayed portion of
pt ctoral fin not continued to the snout; electric organ
.absent, viviparous. Tropical and sub-tropical.
~
Family Torpedinidae.
v-Example Torpedo.--With an electric organ between
the pectoral fins and the head and occupying the whole
Bpace between the the dorsal and ventral integument,
and consisting I)f vertically arranged columns supported
by walls of connective tissue and divided by horizontal
septa of the sam..: material into a number of compartments
filled with gelatinous tissue through the middle of which
runs a horizontal plate composed of a fine granular
nucleated substance and of numerous nerve endings.
Shocks from these can disable a man. Mediterranean,
Atlantic and Indian Oceans.
Family Rajidae.
Example Raja.-Skates. Disc broad and rhombic;
pectoral fins not extended to the front end of the snout;
214
CLASSIFICATION
caudal fin rudimentary; males with patches of claw-like
retractile spines on the upper side of the pectoral fin.
Seas of both hemispheres.
Family Trigol1idae.
Example Trygon.-Sting-rays. Tail long and slender
and with long serra"ted spine. Temperate and tropical seas.
/
Family M yliobatidae.
Example Myliobatis.-Eagle-rays. Large pect()ri\!
fins which are not present at the side of the head b~,
reappear at the extremity of the snout as a pair of detach-cd fins; tail long thin and whip-like; vi.viparous.
Temperate and tropical seas.
----- - _ .
Sub-order Notidani-\Vith six or seven branchial
apertures and a small spiracle; with one dorsal fin without
spine. Vertebral column imperfectly segmented.
Example
Heptanchus.
Chlamydoselachus,
Hexanchus
I
'and
Sub-class Ganoidei.-Fishes with scales embedded'
in the dermis and frequently covered by a layer of ganoin.
Fins frtquently possess a single or double row of fulcra
on their anterior edge; with a conus arteriosus, optic
chiasma, free pectinate gills, operculum, abdominal pelvic
fins and spiral valve in the intestine. The oviducts aI]ll
urinary ducts unite and open by common aperture behind
the anus. Skull hyostylic and tail heterocercaI.
Order Chol1drostei.
Example Acipenser sturgeons.-With five rows of
keeled plates in the skin; snout elongated; mouth small
without teeth; four barbels in front of mouth; fulcra on
CLASSIFICATION
215
the dorsal lobe of the caudal fin ; notochord persistent and
unsegmented. Large fishes in the seas and rivers of
northern hemisphere.
~
Order Lepidostei.
Example Lepidosteus Garpike.-Body covered with
thick, rhombic scales arranged in oblique rows and connected with each other by peg and socket articulation;
tail heterocercal; snout much elongated; vertebrae opisthocoelous ; paired fins non-lobate, and all fins bear paired
fulcra; air-bladder with cellular walls; heart with a
long valvular conus. Fresh-waters of North America,
cuba and china.
Order Amioidei.
thin~
A m p l e Amia.-Scales
cycloidal, over lapping
and without ganoin ; fins without fulcra; tail practically
homocercal ; vertebrae solid and amphicoelous; spiracle
absent; air-bladder bilobed, cellular, lung-like and opens
by a duct into the pharynx; heart with small valvular
conus; bulbus arteriosus well developed. Amia approaches
more closely to the teleostei than to I1UY other ganoid fish.
Fresh waters of United States of America.
O~der Crossopterygii. .
Example Polypterus.-Vertebral column 0ssified ;
tail diphycrrcal ; paned fins with scales basal lobe
of which is rounded, tribl1sal and rhipidostichous ; two
jugular plates between the rami of the lower jaw; body
covered with rhombic ganoid scales; dorsal fins numerous;
pelvic fins present. \Rivers of North and Equatorial West
Africa.
~b-class
Teleostei. Fishes with a bony endoskeleton, amphicoelous vertebrae, pectinate gills, four gill-
216
CLASSIFICATION
slits, and a branchial operculum; without spiracle, conus
arteriosus, optic chiasma' and intestinal spiral valve ;
airbladder often present; scales thin, overlapping and in
the form of bony plates; testes not connected with the
kidney and with separate ducts and openings; caudal
fin homocercal. This order includes the vast majority
of living fishes, fresh-water as well as marine.
The sub-class is divided into thirteen orders. In the
following account only a few specialised and interesting
teleosts are described.
Order 5 ymbrallchii.
Example Amphipnous.-Bo'tly eel-like ; scales
minute or absent; paired fins absent; unp!Jired fins
reduced; anus far from the head; air-bladder aho,ent;
gill-openings confluent in a single slit; with a lung-like
branchial sac on each side. Bengal.
Order H eteromi
,Example Fierasfer. Without pelvic fins; vent at
the throat eel-like, small shore-fishes of tropical seas
often living as lodgers in the cavities of holothurians,
star-fishes and bivalve molluscs; often commensal with
the pearl oyster.
Order Hemibrallchii.
/
Example 1. Syngnathus.-Pipe-fishes. Snout produced ; mouth small and at, the tip of the snout. Skin with
bony plates arranged in ringe; gill-openings very sl.:lall
and near the upper pOl:!terior angle of the gill cover ; one
soft dorsal fin ; pelvics absent; males with an egg-pouch
pla~d on the vdntral side of the abdomen, usually formed
of two folds of skin ; eggs retained here till sometime after
hatching.; tail prehensile and with a caudal fin.
CLASSIFICATION
217
'v.(1fxample 2 Hippocampus.-Sea-norse. Tail prehensile ; without caudal fin, rest as in syngnathus .
./
Order Acanthopterygii
~ Example 1. Ditrema.-Fins supported by rigid spines;
pelvic fins far forward. Viviparous fish; eggs develop
in a saccular enlargement ot" the oviduct. Temperate
North Pacific.
~mple 2. Pseudorhombus.-Flat-fishes. Cranium
twisted anteriorly to allow the two orbits to be on the
same side. In the young the two sides of the body are
alike and the eyes normal; body' compressed laterally
lower side of the body colourless; dorsal and anal fins
long and without spines.
~ple 3. Echeneis.-W~th a suctorial,
transversely
laminated oval disc on the upper surface of the head
(modified dorsal fin) ; pelvics thoracic. Found in all seas;
attach themselves to floating objects and other fishes.
Example 4. Dactylopterus.-Flying gurnards. With
pectorals enormously extended in an antero 'porsterior
direction; take short gliding leaps in the air with the
help of pectoral fins.
Order Ostariophysi.
Example Clarias.-Cat-fish. Skin naked ; barbels
present; with an accessory 'branchial apparatus in the
form of It highly vas ular arborescent organ lodged in the
dorsal half of the branchial chamber; are able to cross
land in searoh of other waters. Muddy and marshy waters
.of Africa and l'3outh Asia.
Sub-Class Dipnoi.-Lung-fishes. Specialised fishes
with gills, lungs, external and internal nares, reduced
218
CLASSIFICATION
scales; skull cartilaginous and covered with few largesoutes ; jaws sh?rt ; teeth in the form of orushing plates;
notoohord persistent and unsegment('d ; an operculum
covering the gill apedures; paired fins with unsessmented
cartilaginous axes; caudal fin diphycercal ; lungs are
very efficient respiratory organs ; vascular system and
heart well developed to deal with pulmonary respiration.
Slwamps of Tropical Africa.
Example Protopterus.
OLASS AMPHIBIA.
Class Amphibia is divided into the following four
orders.Order
"
"
"
1.
UrodeIa.
2.
Anura.
3.
Gymnophiona.
4.
Stegocephalia (extinct).
Order Urodela.-Scaleless amphibia with a well developed tail" hich assists in the progression of the animal;
eyes small, sometimes functionless and without lids,
except in salamandridae ; tympanic membrane and tympanic cavity not developed; vertebral column long and
vertebrae opisthocoelous; usually oviparous and mo~tly
aquatic.
Division Perennibrar.chiata.-Larval gills persist
throughout life in the form of three plume-like appendages
on either side; gill-slits present.
2H)"
CLASSIFICATION
Family Proteidae.
~xample
1. Necturus.-vVater Newt. With twogill-openings; eye-lids absent; fore and hind limbs present; fingers and toes four; trunk elongated and is separated by a slight constriction from the depressed head'
and passes insensibly into the compressed tail which is·
bordered by continuous median fin-rays. North America.
I
,
~mple 2. Proteu5..-With three fingers and two
toes; eyes hidden beneath the skin; tail provided with a
caudal fin unsupported by fin-rays. Rest as in Necturus.
Inhabits the Carniola subterranean waters.
Family Sirenidae.
~mple
Siren.-Mud-eeL Body eel-like; gill-0penings three; premaxiIIaries and mandibles tooth:ess but
with horny beaks; eyelids and hind limbs absent; fore
limbs weak and with four fingers. South East United
States of America. o-JUo ~ C;\A-~ Lo..u
Division Derotremata -Larval gills di!lappear but gillopenings are retained by the adult.
Family Amphiumidae.
Example 1. Amphiuma.-Body eel-like; gill-openings two :rairs; branchial arcl1es four; maxillary boneS'
present, both jaws bear teeth; two pairs of very small
and functionless limbs wit.h two or three digits. Swamps
and muddy waters of North America.
Ex~mple 2.
teeth
III
Ambl~stoma.-With a series of palatal
a nearly straIght, transverse line; toes five;
220
CLASSIFICATION
shows phenomenon of paedogenesis.
uma. North and Central America.
Rest as in Amphi-
~le
3.
'21mblystoma and
Axolotl Larva.-In the two.genera.
Triton, the larvae have the power of
developing sexual organs and reproducing (Paedogenesis,
Neotony). The axolotl larva of Amblystoma has a tail
fin ; three pairs of external gills and four pairs of gillopenings. It breeds several times a year and is founri in
a state of nature in various parts of Mexico and the United
States of America. The causes of this phenomenon
appear to be the abundance of food and other favourable
conditions of life.
Division Myctodora.-Adult devoid
openings.
of
bo~h
gill-
Family Salamandn:dae.
Example 1. Triton cristatus.-The crested Newt.
Aquatic newt with eyelids and laterally compressed and
serrated tail; fingers four and toes five; larvae attain
sexual maturity if prevented from metamorphosing. Great
Britain and Europe.
~Example
2 Salamandra-Lafid Salamanders-t- tail
sub-cylindrical and retained throug out life. ~o ~
..u.DXtl-a
Order Anura.
Scaleless amphibia with a large
depressed head and a wide mouth; eyelids 'Yell developed;
nictitating membrane pr8s~nt ; tympanic membranes large
and some times concealed beneath the skin, vertebral
column remarkably short; ribs and tail absent; nasal
apertures far forward and on the extremity of the snout; hind-limbs much lamer than fore-limbs; posterior part
of the tongue is completely free and can be protruded as
a prehensile organ.
CLASSIFICATION
~ple
221
Family Bufonidae.
Bufo.-Toad&.. Teeth absent ; tympanum
usually distinct; fingers free; toes more or less webbed,
tips dilated into small discs; skin covered with ugly
warts.
/"
Family Hylidae.
VExarp.ple Hyla.-Tree-frogs. Upper jaw with teeth;
terminal pha1anges claw-shappcj and swollen at the base
and carry adhesive cushions with which these animals
climb trees ; tympanic membranes large. Excepting
H. Arborea and two other species found in North India
and South China, the rest are exclusivply American or
Australian.
Family Ranidae.
~Ple Rana Pipens.-The skin on the
back of the
female becomes soft and spongy during the breeding
season and the eggs are placed on it by the males. Each
egg singly into a little pouch of the skin covered by a
gelatinous film_ Embryos do not pass through any
larval stage, but are hatched in the adult form. -D-- ~
In addition to the above families the order contains
three more families viz.
Engystomatzdae, Pelopattdae
and Dtscoglossidae
Order Gymnophiona. Vermiform amphibia without
limbs or limb-girdles, tail very small or absent, with numerous small scales pmbedded in the skin arranged in transverse rows; eyes small, functionless and covered by skin;
tympanum and tympanic cavity absent. Burrow in the
surface soil in damp places near streams. Central and
South America, ~uatJrial Africa, India and the Malay
Archipelago.
,
-222
CLASSIFICATION
Example Ichthyophis
gl~
\
Order Stegocephalia. Extinct; salamander-like or
lizard. like ; dorsal surface of the skull completely covered
by dermal bones; with bony dermal plates on other parts
of the body; parietal foramen present. Earliest known
pentadactyle animals.
Examples Branchiosaurus, Dolichosoma and Laby.rinthodon.
CLASS REPTILIA.
Class Reptilia is divided into l,he following super,orders.
Super-order 1.
Anapsida.
Order 1.
"
2.
Super-order II.
"
"
"
Chelonia
Synapsida
Order 1.
"
Cotylosauria (extinct.)
Pelycosauria (extinct)
2. Dicynodontia
3. Theriodontia
4.
Sauropterygia
5.
Ichthyopteryg;ia
Buper-order III.
Order 1.
,.
"
"
"
Diapsida
Thecodontia (extinct)
CLASSIFICATION
Order 2.
3.
"
Rhynchocephalia
Squamata
Sub-order 1.
"
"
"
"
"
"
223
Lacertilia
2. Ophidia
3. Pythonomorpha (extinct)
4.
Saurischia (extinct)
5.
Ornithischia
6. Crocodilia
.7 Pterodactyla textinct)
Sub-order Lacertilia. Lizards. Reptiles with horny
,epidermal scales, movable quadrate bones, transverse anal
,opening, a cloacal bladder and two sacral vertebrae. The
two rami are firmly connocted at the symphysis; eyes
with movable eyelids and nictitating membFane; tympanic
eavity present.
The sub-order contains twenty-one familirs. Only a
few sp('cialised and interesting forms are described below.
Family Agamidae.
Example Draco.-Flying Dragon. Ribs much prolonged supporting a lateral wing-like dermal expansion
by means of which the animal IS able to glide among
trees. Osteoderms absent. fjound III East Indies,
Family Anguidae.
Example Ophisaurus.-Body elongated and snakelike limbs absent but limb-girdles present; osteodermal
224
CLASSIFICATION
plates present on head and' body; eyes with movabfe
lids.
TerrestriaL South East Europe, North Africa,
South West Asia, America and Mexico.
Family Chamaele ontidae.
Example Chamaeleon.~Tongue protractile to It
length equal to that of the body, club.shaped and viscose;
digits arranged in two bundles of tw() and three; eyes
la.rge and covered with a thick granular lid pierced by a
small central opening for the pupil ; tympanum arid
tympanic cavity absent; parietals single, forming a knoblike crest; tail prehensile, coiling ventral wards. Thesfr
animals undergo remarkable changes of colour. Africa •.
Madagascar, India and Ceylon.
Family Helodermatidae.
Example Heloderma.-Gila monster.
The only
poisonous hzard. Body elongated and covered with ugly
tul)crcles; limbs short, well developed and powerful; tail
thick with reserve fat; teeth fang.like and grooved with
labial poision-glands; osteoderms present. Found in
Mexico.
Order corocodilia.-Tail long and with a dentated
dorsal crest, paired in front" but single behind; fore-limbs
with five digits, hind· limbs with four webbed digits;
nostrils at the tip of the long snout, ean be closed; false
palate present; back and belly with transverse rows of
bony plates which are overlapped by epidermal plates;
the plates of the back are pitted, sculptured or keeled;
abdominal ribs and nictitating membrane present; t.~eth
lodged in . sockets ; pubis excluded from acetabulnm;
long prepubis presl:'nt; quadrate immovable.
The two living families of the order are Gavialidae
and Crocodilidae.
225
CLASSIFICATION
Family Gavialidae.
Example gavialis.-Snout long and slender; nasals
widely separate from nasal aperture. India and Burma.
Family Crocodil'idae.
Example 1. Crocodilus.-Head long; teeth unequal;
fourth mandibular teeth fitting into a notch in the upper
jaw; without bony nasal septum and ventral armour;
AfrictL, South Asia; North Australia and tropical America.
Example 2. Alligator.-Head short and broad; teeth
very unequal; fourth mandibular tooth fits into a pit in
the upper jaw; with a bony nasal septum and with ventral
scutes. China and North America.
Example 3. Caiman.-Without bony nasal septum;
dorsal and ventral armour articulated together. Rest as
in Alligator Central and South America.
Order Squamata.
Sub-order Ophidia.-The snakes are elongated reptiles without limbs and limb girdles with the exception of
a rudiment of a pelvic girdle in some, e.g. Pythons). Horny
epidermal scales without oste(}derms. The mouth is very
extensible and even the upper jaw can move relative to
the cranium-quadrate bones ate movable. The middle
ear apparatus is lacking. The tongue is sensory. Some
snakes have poison fangs. The vertebrae are procoelous
and bear extra articulating facets. The lower border of
both temporal vacuities has vanished. The anal opening
is transverse. Without eyelids urinary bladder and
sacrum. The rami of the m,andibles are united at the
symphysis by an elastic ligament.
15
226
CLAS SIFICATIO N
About 400 genera and 1,800 species are known. Very
few fossil forms ~re known.
Family Boidae.
Example Boa.-The pythons-usually large snakes in
which the maxillary and mandibular teeth gradually
decrease in size. The ventral seales are transversely
enlarged. The nostrils are placed between two or three
nasals and these are separated from those of the other
side by small scales. Eyes are functional and free, the
pupil is vertical. Vestiges of hind limbs and pelvis present.
The tail is short and prehensile. Prefer wooded districts,
climbing trees; crush their prey 'in the coils of the body.
World wide in distribution except New Zealand.
Family Vipendae.
Example Russell's Viper.-Nine genera and about
fourty ~pecies of the vipers are known. Of these Russell's
Viper is one of the scourges of India, Burma and Ceylon.
The upper surface of the body is covered with ..;mall,
imbricating, usually keeled scales. The general colour is
pale brown above with three longitudinal series of black,
light-edged rings, often encircling reddish spots. The
under surface is yellowish white uniform, or with small
crescentic black spots. Usual length is five feet.
Family Crotalinae.
Exomple Crotalus.-The Rattle-Snakes. These have
a deep cavity or pit between the eye and the nose, lodged
into the hollowed out maxillary bone hence also lalled
"Pit-Vipers." Crotalu3 has got a rattle at the end of the
tail. The rattle is composed of 8: nu,mber of horny bells
which fit into each other. The terminal bell is in reality
the horny covering of the tail. Now and then some of
the bells break off, probably when worn o~t~ and a new
CLAS SIFICATIO N
227
set gradually replaces them. As the snake moves the
rattle produces strange rattling noise, a shrill sound like
that of a rattling alarm-clock. The upper surfaceȣ the
head is covered with small soales. The supra-ocular shields
are broader often transversely striated. The largest of
Rattle-snaks attains a size of 8 feet.
Family Hydrophinae
Example Enhydrina.-Sea Snakes. The characteristic
feature of the sea-snakes is that the tail is strongly
(!ompressed. All the scales are small, often the ventrals
.are not enlarged. Eyes are small with round pupils. All
the sea-snakes are very poisonous and live in the sea
with the exception of one species of Disteria which is found
jn a fresp. water lake in the Phi lipines. They live on
fish. In the Enhydrina the maxillaries carry two or more
small grooved teeth besides the poison fangs. The back
is olive 0': dark-grey wi,h black transverse bands. The
under surface is white. This speceies is found in the
Indian Ocean.
Family Colttbrinae.
Ex!)-mple Naja.-Naja belongs to sub-family elapinae
which comprise about 150 species. The tail is cylindrical.
The pair of large grooved poison-fangs are separated by
an interspace having from one to three small, fa5ntly
grooved ,teeth near the posterior end of the maxillaries.
The scales are smooth and ·without pits, and are arranged
jnto fitteen to twenty-five oblique rows on the trunk,
although more occur in the region of the neck. The head
is slightly distinct from the neck. Each nostril lies
between two nasals and the internasal. The pupil is
round. The neck region can be expanded int.o a hood as
the ribs of the region spread and move headwards. S(.'veral
'species of naja are known. The cobra is N. tripudians_
A black and white spectacled mark on the dorsal side of
228·
CLASSIFICA'rION
the hood is a characteristic feature of its colouration.
The cobra is widely distributed and ascends to 8000 feet
above. sea level in the Himahyas. ]~arge specimens may
attain six-feet length. The 'cobra prefers places which
afford it a convenient hole to retire into, for instance
deserted hills of termites and ruins etc. It makes itself
at home in inhabited house especially in villages.
Order Chelonia.-Turtles and Tortoises. Body encased
between the carapace and the plastron; single nasal open~
ing ; quadrate immovable; single temporal arcade; usually
with an epidermal exoskeleton of horny platf's; thorl.l cia
vertebrae and ribs firmly fused with the carapace; pectoral
and pelvic girdles within the ribs ; limbs terminated
by cla1vS or paddle like; tpeth absent but the jaw.; have
a horny investment.
Sub-order' Athecae.-Vertebrae and ribs not fused:
with carapace; skin leathery, without horny plates; parietal bones without descending processes; head net retractile; limbs paddle-like. Indian, Atlantic and Pacific
Oceans.
Example Dermochl!lys.
Sub-order Thecophora. Thoracic vertebrae and'
ribs immova bly united with a series of neural and costal
plates; parietals prolonged downwards meeting tbe
pterygoid or separated from them by an epipterygoid.
Example Chelone, TriollYX: etc.
Order Rhynchocephalia. Lizard-like; verte'nae
amphicoelous; quadrate immovable; upper and l(Jwer
temporal arcades present; acrodont teeth; premax'llae
resembling incisors of rodents; mandibular symphysis
ligamentous; skin with horny scales; vertebrae contain
persistent remains of notochord; ribs single-headed and
CLASSIFICATION
229
with uncinate process. At present these animals are
restricted to some small islets in the Bay of Plenty.
Example Sphenodon.
CLASS AVES.
Class Aves is divided into two ord{'rs.
Order I.
"
2.
Archaeornithes.
Neornithes.
Order Archaeornithes.
Example Archaeopteryx.-Oldcst bird known from
the lithographic slates of Solenhofen (Eavuia) showing
avian as well as reptilian features. Teeth embedded in
sockets in both jaws; manus with three clawed digits; a
long tapering tail composed of about twenty separate vertebrat'l present; thoracic ribs without uncinate processes;
.sternum not well developed; vertebrae amphicoelous;
metacarpals free; pelvis and hind limbs avian.
Order Neornithes.-All living birds; metacarpals fused
with one another'; thoracic ribs with uncinate processes;
tail much reduced; pygostyle present.
Sub-order Ratitae.-Flightless birds; sternum without
keel; coracoid and scapula nearly parallel; palate dromaeognathus; upper articular head of quadrate undivided;
barbs of feathers disconnected, the barbules without
hooks; syrinx absent; wings reduced in size; pygostyle,
uncinate process, and pterylae absent.
230
CLASSIFICATIO N
Family Struthionidae.
Example Struthio.~Ostrich. With naked head and
neck; neck long; legs powerful ; pes with only two digits.
viz. 110S. 3 and 4; feathers without aftershaft. Inhabit.
the plams and deserts of-Africa and Arabia.
Family Apterygidae.
Example Apteryx.-Kiwi. Small; four-toed; neck
short; beak long and weak having the nostrils near theextremity; feathers without aftershaft and are long,
hair-like ansi hang down loosely; wings vestigial, hidden
and functiona) ; eyes remarkably small; legs short, powBrful and scaly; nocturnal. New Zealand.
Family Rheidae.
Example Rhea.-With partially feathered head and
neck, with three-toed feet, and with ischiadic symphsis.
Feathers without aftershaft. South America.
Family Casuaridae.
Example Casuarius.-With high, compressed beak;
helmet-shaped bony knots on the head; with short p.eck,
and thrpe-to('d f('ct. Aftershaft as large as main shaft.
Australian region.
:FamiliE's Dinomitlzidae (Moas) and Aepyornithidae are
extinct.
Sub-order Carinatae.-Inclm1cs grC'at majority 01
birds, palatines and ptcrygoids articulate with the basisphenoidal rostrum; quadrate triradiate; basipterygoid
processes present or a.bsent; sternum with keel; coracoid and scapula nearly at right angle; barbules carry
hooks.
231
CLASSIFICATION
CLASS MAMMALIA.
Class mammalia is divided into the following sub.
classes : Sub-class 1.
"
"
Proto theria
(Monotrema ta)
2. Metatheria
(Massupia lia)
3.
(Placentalia ).
Eutheria
Sub-class Prototheria.-Mammary glands without
teats; pectoral girdles with large coracoid, T-shaped
interclavicle and precoracoids; vertebrae without epiphyses; ribs with single capitulum ; marsupial bones
present; true teeth absent in the adult; ear without a
pinna; male with a horny spur on the hind leg; right
auriculo-ventricular valve incomplete; testes abdominal;
urpters open into a urinogenital sinu.s which communicates with the alimentary canal; cloaca present; brain
simple and without corpus callosum ; eggs large and
meroblastic and laid at an early stage; body temperature relatively low. But. these animals are undoubtedly
mammals because of the presence of hairs, warm blood,
non-nucleated blood-corpuscles and a left aortic'arch.
Family Echidnid{1e.
Example Echidna.-Spiny-anteater. Skin covered with
spines and 'hairs ; snout elongated; tongue long
and protractile ; tail very short ; with an anterior
abdominal vein, five cldwed digits on each limbs and a
temporary pouch in which the single egg is placed.
Burrows in sand and earth.
Australia. Tasmania and
New Guinea.
Family Ornithorhynchidae.
Example Ornithorhynchus.-Duck-billed platypus.
Body covered \, ith a dense soft fur; flnout broad, elonga-
232
CLASSIFICATION
ted and covered with a leathery skin produced into a
fold at the base of the snout; molar teeth horny; f('et
webbed; aquatic in habit and burrows in the banks of
streams ; lays two eggs in a nest. Australia and Tasmania.
Sub-class Metatheria.-Marsuplals. Mammary glands
have teats and enclosed in a marsupial pouch in which the
young are carried ; coracoid reduced to a process of scapula; epipubic bones present; va~ina double; scrotum
in front of penis ; anus and the opening of mino-genital
sinus enclosed by a common sphincter muscle; posterior
part of the palate with vacuties; tympanic bulla, formed
by alisphenoid; corpus callosum and fossa ovaHs absent;
only the last premolar is replaced; glans penis bifurcated;
an allantoic placenta, is absent. Metatheria are ccnfint'd
to the Australian region (with the exception of New
Zealand) and to South America.
Order Didactyla.-Marsupials with all toes separate;
usually with more than i incisors (polyprotodont
dentition) ; marsupium opens ventrally or posteriorly.
Examples Didelphys (Oppossums of America), Dasyurus, Thylacinus etc.
Order Syndactyla.-Marsupials with the second
and third toes of the hind foot united by a common
sheath. Pouch opens forwards.
Examples Perameles (Bandicoots of Australia), Phascolyms (Womoat), Macropus (Kangaroos) etc.
Sub-class Eutheria.-The "higher mammal,\".
Frino-genital organs mostly open independently of the
rectum, vagina generally single, marsupium and epipubic
bones absEnt; mammae and mamma,ry glands present;
tympanic forms a bulla embryo with allantoic plact'nta;
carpus callosum well developed ; testes generally pass
OLASSIFIOATION
:into a scrotal sac which
hind the penis.
i~
233
placed at the sides of or be-
Order Edentata.-Teeth absent from the anterior
!part of the mouth; with scratching or curved claws on
the extremities; with numerous rootless grinders.
Family Manidae.
Example Manis.-Pangolins. Edentlflous, cove.red
with large overlapping epidermal scales which can be
erected and with hairs between the scales; tongue long
and extensile, limbs short and carry five digit8; walk
.on the dorsal surfaces of the claws of their fore-feet and
on the soles of the pes. Terrestrial and burrowing; can
Toll themselves into a ball.
Other examples of the order are Tatusia (Armadilloes)
Myrmecophaga (Anteaters), Bradypus (Sloths) etc.
Order Sirenia.-Sea-cows. Short necked; thick
skinned; naked or with very sparce hairy covering;
·external nares anteriorly directed; pinna absent; two
pectoral mammae ; fore-limbs paddle-like and very
mobile; hind limbs absent; tail horizontally expanded
into a caudal fin. Large herbivorous· animals adapted
to life in estuarine waters or shallow seas of South America, Africa, Oriental region and Australia.
Example Manatus and Halicore.
Order Cetacea.-Wbales and Dolphins. Body fishlike and streamlined, naked, but with a thick layer of
,sub-cutaneous blubber; nasal apertures on the top of the
head; caudal fin horizontally expanded; fatty dorsal
fin present; external ear minute and devoid of a pinna;
.eyes very small and at the angle of the mouth. Live in
2~4
CLASSIFIC.A. TION
'schools' (herds) and swim with grl~at strength and speed;
camivorous and predaceous; found in all seas.
Sub-order Mystacoceti.-Whalebone whales. Without teeth.
Example BalaEma.
Sub-order Odontoceti.-Toothed whales.
With
nUJ)1erous small homodont and monophyodont teeth.
'Example Platanista Gangetica.
Order Hyracoidea.-The biblical Conies. Small
rabbit-like creatures with close set fur, emaIl ears and a
split snout; tail reduced. Most of these live on the
ground except Dendrobyrax which lives in tre(~s. Inhabit Africa.
Example Procavia.
Order Proboscidea.--The elephants.. Large animals
with enormous head; with a long, mobile proboscis serving aA a prehensile organ; nostrils at the end of the
proboscis; limbs massi,-e; bemiplantigrade; inci&ors of
great size and form tusks; canines and premolars absent;
molars lophodont. Love dark and shady forests; herbivorous. "fith only two species confined to Africa and
Indi \ (induding Ceylon, Burma, Malaya, Sumatra' and
Cochin China).
Examples Elepbas indicus and Elepbas africa 'IUS.
Ortrer Artiodactyla.--The Even-toed Ungulates.
Herbivorous; usually of large size; digitigrade; the axis
of the limbs passes between digit,s nos. 3 and 4, these
digits bein:; symmetrict.l an~l having their metapodia.
CLASSIFICATION
235
closely applied together or united into a cannon bonc;
digits bear hooves ; cheek teeth either bunodont or solenodont ; alisphenoidal canal absent,; femur without t,hird
trochanter; dorso·lumbar vertebrae thirteen; stomach
simple. Distributed aU -over the world except Australia
and New Zealand.
Examples Sus (Pigs), Hippopotamus
Cervus (Deer), Ovis (sheel?) etc.
Oamelus
Order Perissodactyla.-The Odd-toed Ungulates.
Axis of the limbs passes through the middle of the digit
no. 3 and the toes of the hind foot are never more than
three; premolars and molars alike; first milk molar
replaced; alisphenoid canal present ; nasals expanded
posteriorly'; dorso-fumbar vertebrae more than twenty
two; femur with a third trochanter; tympanic small:
orbits generally open behind; fibula does not articulate
with calcaneum. With only three living gen~ra.
Examples Equus Horses, ·(Malaya, Borneo, Sumatra
and America), - Rhinoceros (India, Java, Sumatra and
Africa).
Order Carnivora
Sub-order Fissipedia.-Terrestrial carnivora with
. large projecting, canines; three incisors; cutting premolars;
m.olars tuberculate; carnassial teeth present; clilVicles
absent or reduced; scaphoid and lunar fused in the carpus;
lini'bs unguiculate and provided with strong claws; orbits
not closed behind; sagittal crest formed at the union
of parietals; tympanic forms a bulla ; zygomatic arch
is strong and stands well out from the cranium to allow
for the powerful jaw muscles; gut short.
Example Felis, (Cat), Canis, (Dog) etc.
'236
CLASSIFICATION
Sub-order Pinnipedia.-Aquatic carnivora with short
"pentadactyle limbs; digits united by It membrane; nails
.small or absent; incisors conical; molars and premolars
alike; cranium rounded and capacious; tail short. Aquatic, mainly marine, but some ascend rivers; or inhabit
inland seas and lakes.
Examples Of aria (eared seals), Trichechus (walrus),
Phoca (Seals) etc.
Order Rodentia.-Small; herbivorous; plantigrarle ;
unguiculate, incisors large, sharp, rootless and chiselshaped; canines absent; with wide diastema betwcen
incisors and check-teeth; articular surface of the lower
jaw longitudinally elongated; jaw muscles much enlarged;
clavicles absent; brain little convoluted; caecum large;
body covered with fine fur which may be modified llto
spines nails usually claw-like; the habit of gnawing food
is universal.
Examples Sciurus (Squirrel), Castor (Beaver), Mus
(Rats), Hystrix (Porcupine), Lepus (Hares and Rabbits)
·etc. ,
Order Insectivora -Very primitive ; small; covered
with f1?-r or spines; plantigrade or semiplantigrade ; g6nerally pentadactyle, unguiculate feet; digits with claws;
,extremity of muzzle projects beyond the end of the man,dible ; incisors, canines and premolars not differentiatlJd ;
molars rooted and tuberculated; skull elongated and
depressed ; orbit not enclosed. by bone ; palate with
vacuities; jugal weak or absent; testes never descend
into scrotum; cerebral convolutions abse n t. \Videly dIStributed ovc'r the earth's surface; ab3ent from Australian
,regio-n and South Ameri~a.
Examples Talpa (Mole), Tupaia (Trec-shrews), Erinaceus t Hedgehogs I, Sorllx (Shrews) etc.
CLASSIFICATION
237
Order Chiroptera.-Nocturnal; flying mammals ;
forcl·limbs modified as wings; second to fifth digits greatly elongated to support a broad web of skin exten:iing
back to the hind-limb; wing comprises of the antebrachium, the wing membrane and rthe inter-femoral; tail,
if present, is included in the patagium; sternum with a
keel; ulna vestigial; pollex small; knee directed bltck
wards; cerebral hemispheres smooth; teeth heterodont.
and diphyodont; penis pflndent ; testes abdonimal.
Sub-order Megachiroptera.--Frugivorous ; large
animals; snout elongated; foliaceous appendages absent;
second digit of manus with a claw; molars devoid of
cusps. Tropical and sub-tropical regions of Eastern
Hemisphere.
Example Pteropus (Flying fox)
Sub-order Microchiroptera.-Insectivorous; small
animals; snout short; foliaceous appendages present;
second digit of manus without a claw ; molars wi th sharp
cusps. Tropical and temperate regions of both hemispheres.
Example Vespertilio and other ordinary bats.
Order Dermaptera.-"Flying lemurs". With hairy,
muscular parachuting patagium extending from neck to
the wrist and down the sides of the body to the ankle
and thence to the tail; brain primitive; lower incisors
comb-like; molars multicuspidate.
Examples Cynocephalus and Galeopterue.
Order Primates,
Sub-order Lemuroidea.-SmaIl, nocturnal animals
with a long nonprehensile tail; opposable pollex and
238
CLASSIFICATION
hallux; low brain case; uncovered cerebellum. Orbit
not_completely Sh'lt off from tempo-ral fossa; jugal posteriorly extended; nasals large; humerus with entepicondylar foramen; femur with third trochanter; lower
incisors procumbent; lower canines incisiform; second
toe and finger with a sharp claw; tympanic ring pnclosed inside the bulla, uterus bicornuate. Madagascar,
Africa and the Oriental region.
Examples Lemur, LOl"ls etc.
Sub-order Torsioidea.-With large eyes and ears,
long thin tail tufted at the end, very long tarsus, fingers
and toes ending in flatt~ned discs; inner upper mcisor
large and in contact with its fellow; molars with nuwerous
pointed cusps; orbit largely separated from temporal
fossa; digits two and three of the pes with claws; calcaneum and navicular elonga"cd. Indo-Malaya Archipelago
and Phillipines.
Example Tarsius spectrum.
Sub-order Anthropoidea.-Cranial cavity spacious
ancJ rounded; orbits look forward and shut off from
temporal fossa; dentition complete, with bunodont
premolars and molars; two thoracic mammae; humerus
without entepicondylar foramen; radius and ulna separate;
thumbs opposable; femur without third trochanter:
hallux opposa hIe·; cerebrum covers cerebellum; uterus
without cornua.
Group Platyrrhina.-New-World Monkeys.
With
broad nasal septum; three premolars; tympanic ring
forms a bony canal to the external auditory meatus; tail
-may be prehensible.
CLASSIFICATION
Family Hapalidae.
Example Hapale.
Family Cebidae.
Examples Cebus, Ateles (Spider Monkeys), Mycetes
.(Howlers) etc.
Group Catarrhina.-Old-World Monkeys and Apes.
'With narrow nasal septum; two premolars; bony external
-auditory meatus, ischial callosities, and cheek-pouches
present; tail not prehensile.
Family Cercopithecidae.
Examples Macacus ; Papio (Baboons), Cercopithecus
·etc.
Family Simiidae.
Examples Hylobates (Gibbon), Gorilla, Simia (Urang),
Pan (chimpanzaee) etc.
Family Hominidae.
Example Pithecamhropus,
.Homo (Man).
Sinanthropus,
and
APPENDIX
PROTOCHORDATES
The group chordata is divided into two sub-phyla (i~
sub-phylum acrania and (ii) sub-phylum craniata. Thecraniata are more highly organised chordates including
the vertebrates; whereas the acrania or protochordata
are simple or aberrant cnordates devoid of skull (hence
acrania). The proto chordates fall into three classeshemichordata (acorn worms), urochordata (tumnicates
or sea-quirts) and cephalochordata (lancelets).
I. Class: Hemichordata.-Worm-like marin" animals differing from the chordates in many respects. Thebody is not segmented.metamerically but is divisible into
three main regiol1s-pre-orallobe (proboscis), collar and
trunk. The anus is triminal therefore thl're is no postanal tail. The notochord is restricted to the proboscis,
region and develops rather late in the embryo. The
hemichordates are grouped into two orders.
Order: Enteropneusta.-Elongated wormlike burrowing animals with numerous gill-slits; ciliated glandular
epidermis.
Example Balanoglossus.
Order: Pterobranchia.-Sedentary, oolonial animals ; the pre-oral lobe bears ciliated tentacles; gill-slits.
two in number or absent.
240
:?41
APPENDIX
Type: BALANOGLOSSUS.
A.
External characters.
Take out a specimen of balanoglossZts in a dish and
examine its characteristic features and sketch.
(i) The proboscis is more or less oval muscular structure which helps in digging holes. The mouth lies at
its base, on the ventral side, covered by the anterior edge
of the collar. The mouth remains constantly open.
(ii) The coilar is band shaped muscuiar structure
externally very smooth. ,It .helps. in burrowing.
,
..
(iii) The trunk is the last portion of the, body differentiated into the anterior brancbio-~enital region having
gill-slits, the hepatic re~ion •. the. ab<,lominal', regbn
and the caudal regions. ~n the hepatic region,am ~Elen a.
number of finger-like outgrowths of the sid~s. . ~hey.
are actually the projections of the alimentary canal called
hepatic diverticula. 'Che. anus is sit'uatedf at the terminal
end of the trunk.
.1'
B.
Structure of body wall.
Examine a transverse section·oJ the bod.y wall carefully
and sketch.
.i' ( •
(i) The ciliated epithelium forms the outermost
layer. Seattered here 'and' there are seen
unicellulaI' gland cells.
',ii) The circular muscle f~bres form the next
layer underlying the ciliated epithelium.
16
24:.:
APPENDIX
(iii) The longitudinal muscle fibres form
innermost layer.
C.
t
e
The internal anatomy.
1. Examine transverse section thr01tgh the posterio
region of the proboscis of the animal, 110te the following alt/
sketch.
(i) The body wall as described above with section
of strong proboscis musculature.
(ii) The proboscis cavity in the middle.
(iii) The proboscis gland in section.
(iv) The notochord in section.
2. Examine a transverse section through the branchiogenit"l region of balanoglossfts and note the following structures.
(i) The body wall as usual.
(ii The gill-slits opening behind into the gillpouches.
(iii) The gill-pouches are two:, one on either side
opening into the pharynx: through the gillpores.
(iv) The enteron is divided into two regions la) an
upper respiratory and \b) the lower digestive region which is glandular.
I{V) The gonads are seen closely associated with
the gill-pouches in sections of mq,ture specimens.
APPENDIX
243
Also ,examine a longitudinal section passing through the
anterior part of the body and transverse sections thro16gh the
collar and through the posterior part of the trtmk, if available, and note important characters.
II. Class: Urochordata.-Remarkable ciliary-feeding marine animals-the sea-squirts and their allies.
Except members of one group the most are sedentary.
The chordate characters are lost in the adult. Hut their
free-swimming larvae possess important chordate characters. The notochord is found in larval stages only
restricted to the tail (hence urochordata). A we11 developed endostyle is present. At metamorphosis the .larvae
settle on the sea-floor to which they adhere by means
of glandular papillae on the head. Rapid growth in size
takes place and the animal undergoes retrogressive
metamorphosis with the result that (i) the larval
nervous system is lost; (ii) the body becomes surrounded
by a gelatinous or horny eoat the tunic or test; (iii) the
number of stigmata increases and the pharynx becomes
enlarged; the stigmata open into an ectoderm lined cavity
the atrium; and (iv) the tail is cast off and with the tail
the notochord is also lost.
Order: Larvacea.-1!'ree-swimming pelagic forms retaining larval characters in the adult stage. Two gill-slits
only. Atrium absent. The test is thin and periodica11y
cast off.
Example: Oikopleura.
Order: Ascidiacea.-Sedentary animals usually fixed
to the sub-stratum such as the sea-squirts. Often colonial.
Reproduction
by sexual methods.
Metamorphosis
complete.
Example: Ascidia, Clavelina, Botryllus,
Pyrosoma.
244
APPENDIX
Order: Thaliacea.-Large free-swimming forms with
transparent gelatinous test. MuscleH of the body wall
arranged in distinct bands, encircling the body wholly or
partially. l'wo distinct phase!! in the life history which
differ from one another structurally (Polymorphism);
besides one reproduces sexually and the other asexually.
Example: Salpa, Doliolum.
Type:
A.
ASCIDIAN.
External Characters.
Take out an ascidian, keep it in a dish before you
and note down tlte outstanding features.
(i) The tunic or test is the thick outermost
C:1Ve-
lop secreted by the epidermal cells of the
body wall it covers the body entirely.
(ii) The peduncle or the base fixes the animal
to the sub-stratum.
(iii) There are two openings at the distal end (a)
the oral pore and (b) the atrial pore.
The atrial aperture is dorsal the britnchial
(oral) aperture is terminal and indicates the
morphological anterior end of the animal.
Each opening is surrounded by a fringe of
the tunic .
.B.
The Body-wall.
Study a transverse section of the body wall and note the
following ·structures.
(i) The tunic forms the outermost layer. It
consists of test cells embedded in the hyaline
matrix of tunicene.
APPENDIX
"
245
The mantle is the next layer. It consists of
(a) outer epidermal layer made up of a single
celled layer and (b) the muscle fibres and
blood vessels.
(ii)
C. The
pharyn~eal
wall.
Carefully separate the pharyngeal wall from the mantle,
and make a permanent balsam preparation (see page 171
for method). Examine and sketch.
Note the following structures.
(i) The
sti~mata.
(iiI The primary
~ill-bars.
(iii) The secondary
~iIl-bars.
(iv) The synapticulae.
D. The Tailed Larva.
The embryo hatches as a tailed larva which leads a
free-swimming existence for a short time. This stage is
the highest in its chordate organisation when the larva
-swims actually through the sea, by vibrating its long
tail. The larva soon develops adhesive papillae. The
heart and pericardium develop as a diverticulum from the
stomach. After leading free life for some time the larva
attaches itself to the sub-stratum and the retrogressive
metamorphosis sets in.
Examine' a preparation oj the tailed larva oj ascidialt
and note tlte jollowing structures.
(i) The notochord embedded in the tail.
24 Ii
APPENDIX
(ii, The brain with the nerve chord, the' eye
and the otocyst etc.
(iii) The mouth, the pharynx with stigmata,
the endostyle and the stomach.
(iv) The atrium just beginning to develop
around the last parlj of the alimentary
tract.
(v) The adhesive papillae.
n T. Class: Cephalochordata. -The Lancelets.
Marine, sand inhabiting animals, fish-like in appearance,
possessing chief chordate characters.. The notochord is
persistent throughout life and extends the whole length
of the body even to the tip of the snout (hence ctlphalochordata). Pharynx is large and sac-like with numerous
gill-slits. There is a prominent endostyle and a definitely
ciliated tract answering the ciliary feeding habit. The
gill-slits open into the atrium. There is a definite coelom.
Excretion carried through definite nephridia. Metamerism is well marked.
Example: Branchiostoma (Amphioxus).
Type:
A.
AMPHIOXUS.
External Features.
Examine a specimen of amphioxHS.
Fish-like elongated body pointed at both the endsand bears fins.
(i) The dorsal fin ext.ends as a fold of skin
along the whole length dorsally. \.
APPENDIX
247
)i) The "ventral fin is on &he ventral side ex-
tending about a third of the length of the
body from the posterior edge. At the tip
of the tail it is continuous with the dorsal
fin.
(iii) The metapleural folds are two down.
growths from the dorso-Iateral body wall
extending from the atriopore to the oral
hood•
.(iv) The oral hood. At the anterior end the
dorsal and lateral parts of the body project
forward to form a hood, the oral hood.
Posteriorly the oral hood is continuous with
the metapleural folds. From the edge of
the hood arise about twenty stiff tentaclelike processes, the oral cirri. The under
side of the oral hood bears a complicated
series of a ciliated grooves ood ridges which
collectively from the wheel organ.
(v) The atriopore is situated on the ventral
side just where the ventral fin ends and the
metapleural folds begin.
B.
The pharyngeal wall.
Take out a small piece of the pharyngeal wall of
amphioxus and make a permanent preparation (see page
.J, 71 for method). Examine and sketch.
Note
(i)
The primary rods forked at their ventral
ends.
(ii) The secondary or tongue bars.
(iii) The synapticula, cross connections of the
primary 8S well as secondary bars.
248
C.
APPENDIX
Internal Anatomy.
Examine transverse sections of the amphioxus passing
through the pharyngeal region.
Note the following
~tructures
s"k~tch.
and
(i) The dorsal fin on the dorsal side supported
by fin-ray.
(ii) The metapleural foMs
ventral side.
are two on
tJw
(Iii) The body wall consists, of
(a) The epidermis, the outer layer wJnsisting
of a single layer of cubical epithehal cells
~ which bea.r a thin 'but a distinct cuticle.
(b) The fibrous connective tissue forma a.
continuous tough layer below the, epidermis.
;
~
(0) The segmentally arranged muscle blocks,
the myotomes' 'or myomeres form the
greater part of the body wall ..
tiv} The neural tube is situated dorsally abovethe notochord.
(v) The notochord appeo.rs, more or 1008 circular in section, below the neural tube.
(vi) The pharynx occupies the wh9Ie of the
coelom which is extremely reduced in this
region. The pharvngeal wails show thE}
gill-slits and gill-blll'a etc. in sections.
APPENDIX
219
(v) The gonads lie in the ventral part of the
lateral body wall in the pharyngeal reg.ion.
A section through the pharyngeal reglOn,
therefore, will show the gonad toward its
ventral margin.
2. Examine transverse sections through the region of the
intestine behind the atrio pore, ani through other sitch regions,
study und sketch in the manner described above.