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ALBERT R. MANN LIBRARY

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UNIVERSITY OF EDINBURGH
ZOOLOGICAL LABORATORY.

 

E DISSECTION

 

 

 

OF

THE FROG,

BY

J. COSSAR EWART, M.D.,

REGIUS PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF EDINBURGH.

 

EDINBURGH:
JAMES THIN, PUBLISHER TO THE UNIVERSITY.
1887.
THE FROG; Rana temporaria and R. esculenta.

Examine a living frog in an aquarium, noting,—the walking, leaping, and swim-
ming movements ; the colour of the skin under different circumstances ; the attitude
when at rest; the depressed rounded body ; the absence of a neck and tail, the short fore
limbs and the inverted manus; the sacral “ hump” at junction of vertebral column
with urostyle ; the long femur and crus, and the greatly elongated webbed pes. Study
movements of external nostrils and floor of mouth in respiration ; the elevation and
depression of lower eyelid, and, if possible, the method of feeding ; and in the male
edible frog the expansion of the vocal sacs during croaking.

A. External Characters.

1. Make an outline sketch of the frog from the side, and indicate—
(a) The mottled colour of the skin.
(b) The eye, with the semi-transparent lower eyelid half raised.
(c) The interocular gland and the dark patch behind the eye containing
the tympanic membrane.
(d) The extent of the gape, the position of the external nostrils, and the
opening of the cloaca.
2. Sketch—
(a) The manus (4 times nat. size), showing callosities on palmar aspect,
and if a male the swollen cushion at base of index.
(6) The pes (2 nat. size), showing the long tarsal region and the
webbed digits.
3. Number the digits in both limbs from within outwards, noting the short
hallux (I) with a spur at its base, and the long IV. digit of the pes.
4, Examine (low power) and sketch—
(a) A portion of the web showing the branched pigment cells and the
blood-vessels.
(6) A portion of the epidermis, showing openings of unicellular and
spherical cutaneous glands.
B. Buccal Cavity.
1. Open mouth, and note-— ;

(a) The premaxillary, maxillary, and vomerine teeth, the projection of the
eyeballs, the internal nares and Eustachian tubes.

(b) The absence of mandibular teeth, the position, form, and mobility of
the tongue, the lingual veins; the glottis and wide cwsophagus, and
if a male edible frog the openings into the vocal sacs.

2, Sketch—

(a) The roof of the mouth, showing a bristle passing from one of the external
nostrils into the mouth, and another through the drum of the ear
along the Eustachian tube.

(b) The floor of the mouth, showing the tongue connected to the hyoid
cartilage, the glottis, and (if present) the openings of the vocal sacs.

C. Circulatory, Respiratory, and Alimentary Systems.

1. Fix the frog on its back by means of pins through the fore and hind limbs,
cover with water, and divide with scissors the skin along the middle line
from the pelvis to the mandible, noting the large subcutaneous lymph
spaces.

2. Pin back the skin, and make a sketch showing—

(a) The anterior abdominal vein running along the middle line under cover
of the abdominal walls, to disappear behind the large xiphoid
cartilage of the sternum.

(6) The right and left cutaneous and the brachial veins uniting under the
pectoral muscles, the lingual and maxillary veins, and the hypoglossal
nerve,

(c) The mylohyoid muscle, the sternal and abdominal portions of the
pectoral muscle, the rectus abdominis, obliquus externus and obliquus
internus muscles.

3. Make an incision along the wall of the abdomen a little to the left of the
middle line, and observe under the right portion the anterior abdominal
vein which originates from the pelvic veins, and after receiving the small
cystic, parietal, and cardiac veins, divides to enter the right and left lobes
of the liver.

4, (a) Carefully detach the abdominal vein from the muscles, or make an incision
a little to the right of the vein, and reflect the abdominal walls ; note the
peritoneum lining the body cavity, and covering the viscera.

(b) Remove the sternum and ventral portion of the pectoral girdle, so as to
expose the heart and lungs, taking care not to injure the abdominal or
cutaneous veins.

5. Indicate in an outline drawing of the fros—

(a) The heart lying within the pericardium.

(6) The lungs,—if collapsed, they should be inflated by introducing a

blow-pipe through the glottis.

(c) The fibres of the rudimentary diaphragm attached to the cesophagus

and the pericardium.

(d) The entire right and divided left lobes of the liver, and the gall bladder.

(e) The anterior abdominal vein entering the lobes of the liver, and its

cystic and cardiac branches.

(f) The exposed portions of stomach, duodenum, small and large intestine,

the mesentery, and mesenteric veins.

(g) The bilobed bladder which, if necessary, may be inflated from the cloaca.

(h) Tf a aS the ovaries, corpora adiposa, and the long convoluted

oviducts.
6. Examine the peritoneum, tracing it from each side to the under surface of the
vertebral column where it is reflected as a double layer to form the mesentery
and provide sacs or folds for the abdominal viscera.

7. If a female, examine and remove the ovaries and oviducts. For directions see

age 12.

8. N ae without injuring the peritoneum, the position and relations of the follow-
ing structures to be afterwards examined—

(a) The liver and gall bladder ; (6) the stomach and duodenum, with (c)
the pancreas lying between them ; (d) the small and large intestine,
and (e) the spleen near their junction; (f) the testes yellow oval
bodies in front of (g) the flattened dark-red kidneys; (4) the bilobed
bladder projecting from the front wall of the cloaca.

9. Examine and make a diagram (4 nat. size) of the following veins—

(a) System of the superior vena cava, consisting of—

(1) The external jugular formed by the lingual and mandibular.
(2) The innominate formed by the internal jugular and subscapular.
(3) The subclavian formed by the brachial and the musculo-
cutaneous.
Cut open the pericardium, tilt forward the apex of the heart, and observe
the two superior ven cavee entering the sinus venosus.

(b) System of the inferior vena cava—

The femoral and sciatic veins carry the blood from the hind limb.
Each femoral divides to form a pelvic vein, the anterior branches of
the two pelvic veins by uniting in the middle line give rise to the
anterior abdominal vein, while the posterior branches by uniting with
the sciatics form the renal portal veins.

The system of the inferior vena cava includes—

(1) The renal portal vein which formed by the union of the posterior
division of the pelvic vein with the sciatic, receives the dorso-
lumbar vein (from the posterior walls of the abdomen and
from the oviducts in the female) as it enters the outer margin
of the kidney. |

(2) The anterior abdominal vein formed by the union of the anterior
ends of the two pelvic veins: after receiving cystic, parietal,
and cardiac branches, it enters the liver.

(3) The hepatic portal vein formed by the union of the gastric,
splenic, and mesenteric veins (the splenic usually uniting with
one of the mesenteric veins). It unites with the branches of
the anterior abdominal vein and enters the liver.

(4) The renal veins (4 or 5) which unite to form the inferior vena
cava. The vena cava receives

(7) The ovarian or spermatic veins, and
(i) The right and left hepatic veins, and then opens into
the sinus venosus.

(c) System of the pulmonary veins. Trace the pulmonary veins from the
lungs, and observe that they unite to form a single trunk which opens
into the left auricle.
10. The heart and arteries.
a. The Arteries.

Distend the cesophagus with a cylindrical piece of wood or a roll of paper, and
after carefully cleaning the aortic arches, study and make a diagram (4
nat. size) of the heart, truncus arteriosus, and the following arteries—

(a) The carotid arch, giving off
(1) The lingual artery.
(2) The carotid artery, which arises from the carotid gland, and
divides into an external carotid branch and an internal carotid
- branch—the latter entering the cranium supplies the brain.
(b) The systemic arch (4th arch of fish, 2nd of tadpole) which bending
round the cesophagus unites with its fellow of the opposite side to

form the dorsai aorta. Each arch gives off the following branches
before uniting—

(1) The laryngeal artery.

(2) The cesophageal arteries.

(3) The occipito-vertebral artery.

(4) The subclavian, for the shoulder and fore limb.

The dorsal aorta gives off—

(1) The cceliaco-mesenteric which divides into (i) the cceliac for the
stomach and liver, and (ii) the mesenteric for the intestines and
spleen. The cceliaco-mesenteric sometimes arises from the left
systemic arch.

(2) The urino-genital arteries, for the kidneys, genital organs, and
fatty bodies.

(3) Lumbar branches for the body walls, and a small medium branch
(hemorrhoidal) for the large intestine.

(+) The iliac arteries (the terminal bifurcation of the dorsal aorta)
(which supply the bladder (hypogastric) and the anterior walls
of abdomen (epigastric); each then extends along the thigh as

a femoral artery, and each femoral divides into a tibial and
peroneal branch.

(c) The pulmo-cutaneous arch, dividing into
(1) The pulmonary artery for the lung, and
(2) The cutaneous which supplies the skin of the back and sends
small branches to the side of the head.

The thyroid gland is represented by small bright oval bodies in connection
with the lingual arteries, and between the systemic and pulmo-cutane-
ous arches, the thymus by two small round bodies, one behind each
suspensorium. The spleen lies near the large intestine, and the
adrenal glands are embedded in front of the kidneys.

The mandibular branches of the 5th and 7th, and all the branches of the
9th and 10th cranial nerves, and of the 1st spinal nerve should now
be examined. For description see pages 26, 28, and 32.
10

b. The Heart and Blood.

(a) Examine a drop of blood (high power). Observe—and draw

(1) The oval nucleated yellowish-red corpuscles which, when seen on
edge, have a flattened appearance.

(2) The granular amosboid colourless corpuscles which are few in number
and often provided with two or more nuclei.

(6) Cut out the heart leaving portions of the large vessels attached, and
examine it in a watch-glass filled with spirit. Observe the divisions ;
sinus venosus, atrium, ventricle, and truncus arteriosus.

(1) Open the atrium and observe the septum dividing it into two
chambers; notice the opening of the sinus venosus to the right
of the septum, into the large right auricle and the opening of the
united pulmonary veins to the left of the septum into the small left
auricle,

(2) Open the truncus arteriosus longitudinally, and observe the longi-
tudinal valve which separates the left passage leading to the opening
into the pulmo-cutaneous arches, from the right leading to the carotid
and systemic arches. Observe also the semilunar valves which
separate the synangium from the pylangium and the pylangium from
the ventricle.

(3) Cut across the ventricle and notice the small cavity and the thick
spongy walls.

(c) Make a sketch (6 nat. size) showing the cavities of the heart and truncus
arteriosus, and the various valves.

11. The Larynx and Lungs.

Expose the hyoid apparatus by removing the muscles attached to its under
surface, introduce a probe through the glottis into the right lung, remove
the ventral wall of the laryngeal chamber, and slit up the right lung along
the probe with a pair of scissors.

Examine and sketch (2 nat. size)—the lower jaw to be included in the sketch—

(a) The hyoid indicating the body and the anterior and posterior cornua.

(b) The larynx showing the arytenoid and laryngo-tracheal cartilages, and
the vocal cords stretching across the small laryngeal chamber.

(c) The lungs indicating the sacculated cavity of the right lung in direct
communication with the air chamber.

12. The Alimentary Canal.

(a) Observe the wide cesophagus ; the tubular stomach distinctly separated
from the duodenum by the pyloric constriction, the gall bladder lying
between the divided left lobe and the smaller entire right lobe of the
liver, the bile duct entering the duodenum, the pancreas sending
numerous ducts into the bile duct, the spleen attached to the
mesentery, the small and large intestine, and the cloaca.

(b) Cut across the cesophagus, immediately behind the posterior cornua
of the hyoid and the large intestine at its junction with the cloaca,
and then remove the whole length of the alimentary canal, taking
with it the lungs, liver, pancreas, and spleen, but leaving the dorsal
aorta and kidneys. Uncoil the intestine and make a drawing show-
ing all the structures removed.

(c) Slit open the alimentary canal, and note the longitudinal folds of the
stomach, the pyloric valve, the transverse folds of the duodenum, and
the opening of the common bile duct.
12

D. Reproductive Organs and Kidneys.

1. The female frog.

a. The reproductive organs—

Observe—

(a) The ovaries suspended by peritoneum in front of the kidneys,
the ova projecting from the surface of the ovaries and the fatty
bodies from their upper ends.

(b) The long convoluted oviducts opening in front by small apertures
into the body cavity, and after dilating opening behind into the
cloaca.

Make a diagram showing the ovaries, fatty bodies, and oviducts.

Make an incision into one of the ovaries, and note that the ova project
freely into the central cavity, and that in addition to the mature
dark ova (abundant during the breeding season), there are numer-
ous, almost colourless, developing ova. Examine a portion of
the ovary containing young ova, first with low and then with
high power, and draw an ovum showing the vitelline membrane,
vitellus, germinal vesicle, and germinal spots.

b. The kidneys—

Observe that they lie in a lymph space behind the peritoneum, and
that a simple duct passes from each to open separately into the
dorsal wall of the cloaca.

Make a diagram showing the kidneys, adrenal glands, ureters, and
cloaca.

2. The male frog.

Observe—

(a) The kidneys lying behind the peritoneum.

(b) The testes suspended by peritoneum in front of the kidneys.

(c) The delicate vasa efferentia which carry the spermatozoa from the
testes into the tubules of the kidney.

(d) The duct (Wolffian) which extends from the outer margin of each
kidney to the cloaca, and acts both as vas deferens and ureter.

(e) The vesicula seminalis developed in connection with the outer margin
of each duct—in R. esculenta the vesicula seminalis is represented
by a simple dilation of the common duct.

Make a diagram showing the testes, vasa efferentia, kidneys, common

ducts, vesicule seminalis, and cloaca.

Cut open the cloaca and look for the openings of the oviducts and

ureters, and also for the rectal and vesicle openings.

Examine (high power) a small portion of testis; note and draw the
spermatozoa.

Examine again the dorsal aorta, noting especially the branches to the
kidneys and genital organs, and its bifurcation into the two iliacs, and
then proceed to study the sympathetic nervous system and the 2d to
10th spinal nerves and their principal branches. For spinal and
sympathetic nerves, see pages 30 and 32.
14

E. The Skeleton.

Before beginning the examination of the skeleton the frog may be immersed for
two or three minutes in boiling water.
1. The skull.

a. Remove the skin and subcutaneous tissues from the roof of the skull,
and observe the parieto-frontals and nasals, the premaxille, maxille,
and squamosals, the quadrato-jugals, and the exposed portions of the
exoccipitals, prootics, and sphenethmoid.

b. Remove the mucous membrane from the roof of the mouth, and
observe the parasphenoid and vomers, the pterygoids, and palatines,
and the under surface of the maxille, premaxille, and quadrato-
jugals, and the exposed portions of the exoccipitals, prootics, and
sphenethmoid.

c. Examine the mandibular arch—

(a) The upper portion (quadrate cartilage) known as the suspen-
sorium ; note that it supports the squamosal, and serves by its
lower end for the attachment of the mandible, while it is united
by its upper end to the auditory capsule.

(b) The lower portion or mandible, each half of which consists partly
of cartilage (Meckels), and partly of cartilage bones—the long
angulo-splenial underneath, and the small mento-meckelian at
the symphysis, and the dentary on the upper margin.

d, Examine the hyoid arch, noting—

(a) The columella in connection externally through a piece of cartilage
(suprastapedial) with the membrana tympani, and fixed by its
inner end to the stapes.

(6) The anterior process of the hyoid attached to the auditory capsule
below the fenestra ovalis.

(c) The body consisting of the fused ventral portions of the hyoid and
the four branchial arches of the tadpole.

(d) The ossified posterior processes (remains of fourth branchial
arch) which project obliquely backwards one at each side of the
larynx.

e. Draw (2 nat. size)—*

(a) The hyoid arch, showing the anterior and posterior cornua, and
the short processes from the angles of the body.

(6) The upper surface of the skull, showing—

(1) The membrane bones,—parieto-frontals, nasals, premaxille,
maxille, and squamosals.

(2) The cartilage bones,—exoccipitals, sphenethmoid, prootics,
and quadrato-jugals.

(ce) The under surface of the skull, showing—

(1) The membrane bones,—parasphenoid, vomers, premaxille,
and maxille.

(2) The cartilage bones,—exoccipitals, sphenethmoid, pterygoid,
palatine, prootic, and quadrato-jugals.

(d) The mandible, showing Meckels, cartilage, and the angulo-splenial,
mento-meckelian, and dentary bones.

* The cartilage should be coloured blue, and the cartilage bones dotted by way of
distinguishing them from the membrane bones,
16

(f) Remove carefully, under water, the parieto-frontals, the right nasal,
the right premaxille, maxille, and squamosal. Examine and make
a sketch (2 nat. size), showing the exposed portion of the chondro-
cranium, the large anterior fontanelle, and the two small posterior
fontanelles, the exoccipitals, sphenethmoid, prootics, and quadrato-
jugals ; and, in addition, on the left side, the nasal, premaxille,
maxille, and squamosal.

(g) Remove the skull from the vertebral column, and make a sketch
(2 nat. size) of the posterior aspect, showing the condyles (formed
by the exoccipitals) at each side of the foramen magnum, the
prootics, the columella, and the upper ends of the anterior cornua
of the hyoid, the tympanic ring, and the suspensorium enclosed
between the squamosals and pterygoids.

2, The vertebral column.

(a) Expose and make a drawing (2 nat. size) of the dorsal surface of the
vertebral column, showing the nine vertebree and the long urostyle,
and indicate also the pelvic arch in connection with the large trans-
verse processes of the ninth vertebra (sacrum).

(b) Observe the intervertebral foramina and the intervertebral discs, and
then examine the individual vertebrae, noting that the 2d to the 7th
resemble each other, while the Ist, 8th, and 9th are peculiar.

(c) Make drawings (4 nat. size) of the Ist, 3d, 8th, and 9th vertebre.

(a) The Ist or atlas vertebra. Indicate the forward projection of the
centrum, the narrow arch and rudimentary spine, the concave
facets for the occipital condyles, and the flattened articular
processes for the second vertebra, and note the absence of trans-
verse processes.

(b) The 3d vertebra. Indicate the proccelous centrum, the neural
arch and its spine, the anterior and posterior articular processes
(zygapophyses), and the large transverse processes.

(c) The 8th vertebra. Indicate in a section that the centrum is
amphiccelous.

(d) The 9th vertebra (sacrum). Indicate the single convex anterior
facet for the 8th vertebra, the two convex posterior facets for
the urostyle, and the long expanded transverse processes which
support the ilia.

(d) Make a sketch of the urostyle, showing the two facets in front, the
cartilage projecting from the hollow posterior end, the dorsal ridge,
and the small aperture through which the 10th spinal nerve escapes
from the canal in the front of the ridge.
18

3. The pectoral girdle and sternum. (To be examined in the second frog after
the muscles have been dissected.)

a. The sternum note from before backwards.

(a) The episternum, a smail circular plate of cartilage.

(b) The narrow bony omosternum.

(c) The epicoracoids, consisting of a piece of cartilage at each side of
the middle line between the coracoids.

(d) The sternum proper, consisting externally of bone and internally
of cartilage.

(e) The large bifid cartilaginous xiphisternum,

b. The pectoral girdle. Observe—

(a) The preecoracoid, a narrow bar of cartilage, extending from the
sternum to the anterior margin of the scapula.

(b) The post-coracoid, a flattened bone extending from the sternum
to the posterior margin of the scapula and entering into the
formation of the glenoid cavity.

(c) The clavicle (a membrane bone) ensheathing the anterior margin
of the preecoracoid.

(d) The scapula, a short expanded bony plate which forms the upper
portion of the glenoid cavity.

(e) The suprascapula, a large thin plate of cartilage in which a
limited amount of osseous and calcareous matter is usually
deposited.

Make a drawing (2 nat. size) showing the sternum and pectoral girdle,
colouring the cartilage blue and the clavicle red, in order to dis-
tinguish it from the cartilage bones.

4, The fore-limb.
Remove the muscles and examine the bones, and make a sketch (2 nat. size)
showing—

(a) The humerus with a rounded head, deltoid and condylar ridges, and

a spheroidal articular surface for the radio-ulna.

(b) The radio-ulna concave and simple above, with an olecranon process,

but divided below and presenting three facets for the carpals.

(c) The six carpals—radiale, ulnare, centrale, and three distalia.

(d) The metacarpals and phalanges of the digits—the 1st digit (pollex)

having no phalanges ; the IJ. and III. digits, two phalanges each ;
and the IV. and V., three phalanges each.
20

5. The pelvic girdle.
Note that all three portions of the girdle enter into the acetabulum, the ilium
forming the largest (4), and the pubes the smallest segment (4).
Examine—(a) The ilia, noting the crests, and that the two bones held apart in
front by the long processes of the sacrum unite behind to form an iliac sym-
physis ; (0) the ischia fused together and forming a median crest; (c) the
pubes, represented by a small triangular piece of cartilage. Make a drawing
(2 nat. size) showing the pelvic girdle from the side.
6. The hind-limb, ;
Examine the hind-limb, noting—

(a) The long slender curved femur with a spherical head and a laterally
expanded lower end.

(b) The tibio-fibula, longer than the femur but less curved, and with both
ends expanded and a distinct groove indicating the line of union of
the two bones.

(c) In the tarsal region—

(1) The greatly elongated tibiale (artragalus) and fibulare (calcaneum),
separate in the middle but connected above and below by
epiphyses.

(2) The small distal tarsals and the nodules which support the spur.

(d) In the foot—

The five complete digits; the I. (hallux) and II. with two phal-
anges each, the III. and V. with three each, and the long
IV. digit with four phalanges.

Make a sketch of the hind-limb (nat. size) and of transverse sections of
the femur and tibio-fibula (2 nat. size).
22

F, The Nervous and Muscular Systems and Sense Organs (second frog).

1. Reflect the skin along the back and notice the large lymph spaces, the cutane-
ous branches of the dorsal nerves crossing them, and the position of the
lymph hearts—one at each side of the urostyle, and one within the margin of
each supra-scapula.

2. Examine the following muscles—

(a) The depressor mandibuli, which extends from the skull over the scapula
to the angle of the jaw.

(b) The trapezius, extending from the exoccipital to the dorsal border of
the scapula.

(c) The lattissimus dorsi, extending from the dorsal fascia behind the scapula
to be inserted into the deltoid ridge of the humerus.

(d) The temporal, passing from the auditory capsule to the coronoid pro-
cess of the mandible.

(e) The pterygoid, which rises in front of the temporal and is inserted
into the mandible behind the coronoid process,

(f) The masseter, from the quadrato-jugal to the outer surface of the
mandible near its articulation.

Observe that (d), (e), and (7) elevate the mandible.

The pectoral girdle and sternum should now be examined (see page 8).

After noting, clear away the infraspinatus, levator anguli scapule, and retrahens
scapulee, and also the extensor dorsi communis and intertransversalis muscles,
and the right supra-scapula. Cut across the membrane between the skull and
the atlas, and then remove carefully the roof of the cranium so as to expose the
brain by cutting from the foramen magnum first through the side walls, and
then across in front of the parieto-frontals, Expose the spinal cord and
filum terminale by removing the neural arches and the upper segment of the
canal of the urostyle.

. Remove the pigmented pia mater, note and draw (3 nat. size) the olfactory
and cerebral lobes, the optic thalami (indicating the position of the pineal
gland, probably removed with the roof of the skull), the optic lobes, cerebellum
and medulla oblongata, and the spinal cord (showing the brachial and lumbar
enlargements), the dorsal fissure, and the filum terminale.

. Examine the cavities of the brain.

(a) The fourth ventricle, a triangular space behind the cerebellum roofed
over by a vascular membrane.

(6) The iter, a narrow passage leading from the fourth to the third
ventricle.

(c) The cavities of the optic lobes which communicate with the iter.

(d) The third ventricle situated between the optic thalami and covered by
the choroid plexus. Remove the plexus, noting the hollow peduncle
of the pineal gland projecting from the roof of the ventricle, the band
of fibres known as the posterior commissure, also the infundibulum
projecting downwards towards the pituitary body.

(e) The lateral ventricles. Each communicates by a small aperture (the
foramen of Monro) with the third ventricle, and extends a short
distance into the olfactory lobe.

In an outline sketch of the brain (8 nat. size), indicate the cavities
mentioned.

6. Examine the olfactory bulbs, and expose the olfactory sacs in order to see the

smelling membrane in which the olfactory nerves terminate.
Make a sketch (4 nat, size) showing the two chambers (one opened) and
the olfactory nerves.

ge

ne

ou
24

7. Cut across the medulla, and then raise the cerebral lobes, and after noting cut
as near to the skull as possible the following nerves—
(1) The optic nerves forming the chiasma as they extend towards the
optic lobes.
(2) The 3rd, 4th, and 6th nerves which pass to the muscles of the eye.
(3) The 5th nerve running forwards to escape in front of the auditory
capsule.
(4) The 7th nerve passing out of the skull immediately behind the 5th.
(5) The 8th, entering the auditory capsule.
(6) The 9th and 10th, escaping by an aperture behind the auditory capsule.
8, Examine and sketch the under surface of the brain (3 nat. size), showing the
cerebral lobes, the optic chiasma, the tuber cinereum and the pituitary body,
the crura cerebri, the medulla oblongata, and the roots of the cranial nerves.
9. Examine the eye of the frog, and at the same time the eye of the sheep or ox.
a. The frog—

(a) Remove one of the eyes, and note the cornea, and behind it the
elliptical pupil surrounded by the iris ; also the sclerotic pierced
by the optic nerve. Cut round the equator of the eye and
observe (1) the choroid and retina; (2) the vitreous humour
filling the cavity of the eyeball; and (3) in the anterior portion
the lens, iris, and aqueous chamber.

b. The ox or sheep.

(a) Remove the muscles and other tissues so as to expose the sclerotic
and optic nerve, and note the conjunctiva covering the cornea
and extending over the anterior portion of the sclerotic, also the
iris perforated by the pupil.

(6) After puncturing the cornea and noting the aqueous humour which
escapes from the anterior chamber, remove the cornea by cutting
round the margin, and note the pupil, iris, lens, and posterior
chamber, and the ciliary muscle which connects the outer margin
of the iris to the cornea and sclerotic.

(ce) Separate the ciliary muscle from the cornea and sclerotic ; remove
the sclerotic from the anterior portion of the eyeball; observe
the choroid and the vessels and nerves (ciliary) which reach it
through the sclerotic. Raise a portion of the choroid and note
the retina, and then after cutting through the choroid and retina
by a circular incision midway between the outer margin of the
iris and the equator of the eye, remove the lens and the struc-
tures in connection with it, and examine under water, noting
(1) the anterior portion of the retina (ora serrata) lying within
the choroid ; (2) the circle of folds (ciliary processes) in front of
the ora serrata projecting from the anterior portion of the choroid
to fit into depressions on the outer margin (suspensory ligament)
of the capsule of the lens; (3) the layer of dark pigment (uvea)
on the posterior surface of the iris ; (4) the capsule of the lens,
and the lens after removal from its capsule.

c. Examine next the posterior portion of the eye, noting (1) the vitreous
‘ humour enclosed by the delicate hyaloid membrane; (2) the retina
lying between the vitreous humour and the choroid with blood vessels
radiating in its substance from the point of entrance (blind spot) of
the optic nerve; (3) the lustre of the greenish coloured tapetum
lucidum. _
d. Indicate the structures seen in an ideal section (2 nat. size).
26

10. The III, IV., and VI. nerves and the muscles of the eye.

a. The oculo-motor (IIT.) sending branches to—

(a) The levator bulbi which extends from the side of the skull under
the eyeball to the upper jaw, giving off a few fibres to act as a
depressor of the lower eyelid.

(b) The superior, inferior, and internal recti which arise from the inner
angle of the orbit and are inserted into the sclerotic.

(c) The inferior oblique, which extends from the palatine bone to the
under surface of the sclerotic.

(d) The retractor bulbi which encloses the optic nerve.

b. The pathetic (IV.) supplying the superior oblique which extends from
the palatine to the upper surface of the sclerotic.

c. The abducens (VI.) supplying the external rectus and the retractor of
the bulb.

d. Make a sketch showing the optic nerve, the eyeball, and the muscles
inserted into the sclerotic.

11. The Trigenimal (V.) which passes from the cranium in front of the auditory
capsule and divides into—

a. The ophthalmic branch which extends forwards under the superior
rectus muscle to communicate with the IV. nerve and supply the
Harderian gland, nasal mucous membrane and the skin in the region
of the nasal capsule.

b. The maxillary branch which runs forwards under the eyeball to reach
the lower eyelid and the skin covering the upper jaw.

c. The mandibular branch which, at first continuous with the maxillary
portion, bends round the inner surface of the upper jaw to reach and
extend along the outer surface of the mandible. Look for branches
to the temporal and pterygoid muscles and the skin covering the
lower jaw.

The ganglion (Gasserian) on the root of the V. nerve with which the VI.
and VII. nerves and the sympathic are connected, lies in the foramen
of the pro-otic bone.

12. The facial nerve (VII.) which leaves the skull immediately behind the tri-
geminal and divides into—

(a) The palatine branch which runs forwards under the orbit, and is dis-
tributed partly to the roof of the mouth and partly along with the
mandibular branch of the V. to the front of the palate and the outer
aspect of the mandible.

(6) The hyomandibular branch which runs outwards over the auditory
capsule and columella to the angle of the mouth, where it divides, one
portion extending towards the anterior cornu of the hyoid, the other
running along the inner surface of the mandible to reach the sym-
physis.

13. The auditory nerve (VIII.) which enters the auditory capsule to terminate
in the internal ear. For the anatomy of the auditory organ, see the
“Dissection of the Skate.”
28

The next three nerves (glossopharyngeal, vagus, and hypoglossal) are best
examined in a dissection from below. See page 8. When the mylohyoid is
removed, and the cesophagus distended, the hypoglossal will be seen appear-
ing immediately in front of the brachial plexus, and then arching forwards
in the substance of the genio-hyoid muscle to end in the muscles of the
tongue. About two lines in front of the hypoglossal is the glossopharyngeal.
Tt escapes from the skull behind the auditory capsule, and runs forward at
first nearly parallel to the hypoglossal, but it soon crosses the hypoglossal as
it passes to the base of the tongue. Running obliquely across the space
between these two nerves at a deeper level is the vagus, while crossing the
space it gives off the laryngeal nerve, and, after passing under the hypo-
glossal, it breaks up into branches for the heart, lungs, and stomach.

14. The glossopharyngeal nerve (IX.) leaves the skull along with the vagus
immediately behind the auditory capsule, and divides into—

a, An anterior branch which bends round the auditory capsule to join the
facial nerve in front of the columella,

b. A posterior branch, which, after passing under the petrohyoid muscle
and the hypoglossal nerve, takes a sinuous course between the
geniohyoid and the hyoglossus towards the base of the tongue,
which it enters.

15. The pneumogastric or vagus (X.), which, immediately after passing through
the skull, leaves the IX. nerve and expands to forma ganglion, After giving
off branches to the dorsal muscles, it reaches the walls of the pharynx, and
runs obliquely downwards and backwards to break up into the following
branches—

a. The laryngeal branch, which, passing between the glossopharyngeal and
hypoglossal nerves and over the pulmo-cutaneous artery, reaches and
supplies the larynx.

b. The cardiac, which reaches the inter-auricular septum by passing dorsal
to the pulmonary artery.

c. The pulmonary, which extends along the pulmonary artery to the
lung.

d. The gastric, which extends downwards along the side of the ceso-
phagus to reach the stomach.

Indicate in ventral and lateral views of the head, the distribution of the
V., VIL, IX., and X. nerves.
30

16. The sympathetic nervous system. This system consists of two ganglionated
cords, which anteriorly lie in contact with the vertebral column, while
posteriorly they are in connection with the sides of the aorta. The anterior
pair of ganglia communicate with the 1st spinal nerve and send branches
forwards which, after communicating with the ganglia of the IX. and X.
cranial nerves seem to end in the Gasserian ganglion. Lach of the eight
following ganglia are connected to their corresponding spinal nerves by a
single commissure, while the tenth ganglion has several branches reaching
it from the tenth (coccygeal) nerve.

Numerous small branches pass from the various ganglia to the adjacent
viscera and blood vessels, and a special set of branches (cardiac) arise from
the first ganglion to reach the auricles and the large vessels which pass to
and from the heart, while other filaments, springing chiefly from the third,
fourth, and fifth ganglia, unite to form a plexus (solar) on the dorsal aspect
of the stomach.

Make a sketch showing a transverse section of the spinal cord, the roots
of a pair of spinal nerves, and a pair of sympathetic ganglia connected to
these nerves. Make a second sketch showing the 10 pairs of sympathetic
ganglia, their connections with each other, and the cranial and spinal nerves
and the cardiac and solar plexuses derived from them.
32

17. The spinal nerves, Observe that—

“a. The hypoglossal (1st spinal nerve = XI. cranial of man), escapes
between the first and second vertebre to cross first the vagus and
“then the glossopharyngeal, it next passes beneath the mylohyoid
muscle to reach the base of the tongue. Besides supplying the
tongue muscles, it sends small branches to the muscles of the back
and the floor of the mouth. Add this nerve to the sketch showing
the V., VIL, IX., and X.

b. The second and third spinal nerves unite immediately after escaping
from the spinal canal to form the brachial nerve, which supplies
the muscles of the shoulder, and then extends along the arm to divide
into the radial and ulnar nerves for the forearm and hand.

c. The fourth, fifth, and sixth spinal nerves supply the skin and muscles of
the trunk.

d, The seventh, eighth, and ninth spinal nerves run obliquely back-
wards (forming the larger part of the cauda equina), to escape behind
their respective vertebrae, and unite to form the sciatic plexus. The
seventh, before uniting with the eighth, sends branches (ileohypo-
gastric and crural) to the walls of the abdomen, the skin and
muscles of the thigh. The sciatic plexus condenses to form the sciatic
nerve which extends along the thigh to divide above the knee into
the tibial and peroneal nerves for the leg and foot,

e. The tenth nerve (coccygeal) escapes through a small aperture in the
urostyle, and is distributed to the walls of the cloaca and bladder,
and the other structures in the pelvic region.

18. Make a sketch (2 nat. size) showing the under surface of the brain and spinal
cord, with the origin and principal branches of all the cranial and spinal
nerves on the one side and the sympathetic system and sense organs on
the other.

*,* In preparing the above directions the Author is indebted to Mr J.T. Cunningham, B.A.,
for much valuable assistance,
UNIVERSITY OF EDINBURGH
ZOOLOGICAL LABORATORY.

 

DIRECTIONS FOR THE EXAMINATION

OF

AMCEBA, PARAM(CIUM,
VORTICELLA, HYDRA, LUMBRICUS, HIRUDO,
ASTERIAS AND ECHINUS.

BY

J. COSSAR EWART, M.D.
REGIUS PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF EDINBURGH,
AND

J. DUNCAN MATTHEWS,

DEMONSTRATOR OF ZOOLOGY IN THE UNI\ ERSITY OF EDINBURGH,

 

EDINBURGH:
JAMES THIN, PUBLISHER TO THE UNIVERSITY.
1884,
AMGBA.

Amoebee are often found amongst the deposits of fresh water pools. When a
small quantity of the material containing Amcebe is introduced into a small glass
aquarium, and some fresh water added, a thin film usually appears on the surface
of the water. This film, when examined, will be found to be composed chiefly of
small organisms, some of which are likely to be amcebee.

Take by means of a pipette a small portion of the film, and allow a drop to fall
on a glass slide. Lay a narrow strip of moistened writing paper near to the drop,
and apply a covering glass so that one edge rests on the paper. Look for an Amceba
with a low power, and then examine with a high power, noting that it consists of
an irregular shaped central portion from which blunt processes (pseudopodia) of
various sizes, project, and that when active the form of the body and processes are
constantly changing.

A. Observe—

1. That the body consists of—

(a) A central mass of granular protoplasm (endosare) which extends into
some of the pseudopodia, and usually contains a nucleus, a con-
tractile vacuole, and food particles.

(b) A thin almost transparent outer film (ectosarc) which contains few
granules. :

2. The change in form, the appearance and disappearance of the pseudopodia,
and the movements of the granules. Note that the pseudopodia seem at
first to consist only of ectosarc, but that as some of them increase in size
the granular endosare flows into them, and further that a pseudopodium
may throw out new processes, and then advance, dragging, and ultimately
completely absorbing the body and processes behind it.

B. Draw an Amceba at intervals of one or two minutes to show the changes of
form, and indicate by arrows the directions of the currents of granules.

C, Examine—

1. The food particles, and ndte that they usually lie at first in a small
quantity of water (food vacuole), and that the food may consist of
minute plants or animals, and that in addition to food there are often
grains of sand and other substances. Study the process of ingestion of
the food particles, and the expulsion of the non-nutritious particles, and
note that they enter or escape from any part of the surface.

2. The contractile vacuole, if visible, and watch its pulsations.

3. The nucleus which may be made more distinct by adding a drop of
acetic acid to the preparation.

D. Add to one of the drawings the nucleus, the contractile vacuole, also the food
vacuoles, and any foreign substances which may be present.

E. Look for encysted Amcebe and for Amcebz in process of division by transverse
fission.
PARAMGCIUM.

Paramecium, Stentor and other ciliated infusoria are usually abundant in
stagnant water. Opalina is often found in the rectum of the frog and newt.

Examine a drop of water containing Parameecia with a low power and observe
that they swim rapidly by means of their cilia, and that as they glide along they
usually rotate on their longitudinal axis so as to show distinctly at intervals the
mouth and pharynx on the ventral aspect.

A. Arrange a few fibres of fine cotton-wool over the drop, apply a covering glass,
and examine with a higher power—
1. The Ectosare.
Note (a) The thin cuticular layer perforated for the cilia.

(b) That the cilia form an almost uniform layer except in the region of
the mouth where they are somewhat irregular and longer.

(c) The striated layer, the lines running nearly longitudinally.

(d) The two dorsally placed contractile vacuoles, from which several canals
radiate—observe the rhythmical contractions of the vacuoles.

(e) The trichocysts ; if not visible, they should be afterwards looked for,
when acetic acid or some staining solution has been added.

2. The Endosare.
Note (a) The granules moving in a definite direction.

(6) The nucleus with a nucleolus at its side—may not be visible until
acetic acid is added.

(c) The food entering the endosarc from the pharynx and following the same
course as the granules, the food particles lying at first in food vacuoles,
but at a later stage in contact with the protoplasm.

(d) That the undigested portions of food escape by an anal aperture which
usually appears some distance from the mouth.

B. Some of the Parameecia may be fed with carmine, to show better the course of
the circulation of the food particles, while others should be treated with acetic
acid or stained with majenta, to show the nucleus, nucleolus, and trichocysts.

C, Examine with the low power and note if any of the Paramcecia are in contact
with each other (conjugating) or in process of division by transverse fission.

D. Make a diagram of Paramcecium, showing all the structures referred to, and
draw any other Infusoria that may be present in the preparation.
VORTICELLA.

Vorticellidee are found both in fresh and salt water, adhering to plants, insects,
&c., and when present in considerable numbers appear to the naked eye as little
white tufts.

A. Remove a small piece of weed to which the Vorticelle are attached, place in a
drop of water on a slide, lay a piece of moistened writing paper near the weed, and
apply a covering glass. Examine with low power, and note— _

1. That the colony is composed of a number of individuals, each of which
has a bell-shaped body, supported at its narrow end on a stem.
2. That this stem is constantly being retracted in a spiral form.
3. That during retraction of the stem, the body assumes a spherical form by
the margin being bent closely inwards.
4, In addition look for—
(a) Specimens in process of budding.
(6) The small free swimming buds.
(c) The buds conjugating with adult fixed forms.
(d) Specimens in process of division by longitudinal fission.
(e) The half which becomes free, noting the posterior circlet of cilia
which exists during its free-swimming stage.

B, Examine under high power, and notice—

1. That the bell has the margin bent outwards, forming a thickened edge (the
peristome), and that it is vertically striated near the base.

2. That this peristome bears cilia.

3. That there is a ciliated disk-shaped portion—the epistome—filling up most
of the mouth of the bell.

4, That at one point a space—the vestibule—is left between the peristome
and epistome, and that there is a narrow pharynx continuous with the
vestibule.

5. The stem, consisting of—

(a) An outer generally straight sheath, and
(6) A central striated portion, which has a slight spiral form within the
outer sheath.

6. That on irritation the epistome is retracted, while the peristome is folded

closely over it, so that the body assumes a rounded form, which is fol-

lowed by the retraction of the body by the stem throwing itself into a

spiral form.

. That the body consists of cuticle, clear ectosarc, and granular endosare.

The contractile vacuole near the upper edge of the bell.

. That food vacuoles are present, and that they circulate slowly down one
side and up the other.

Reon

C. Place a few particles of powdered carmine near the vorticelle and notice that
the cilia sweep them into the vestibule, near the bottom of which they are aggregated
into a food vacuole.

PD, Add to the preparation acetic acid or a staining fluid, and note the horse-
shoe-shaped nucleus.
HYDRA; Hydra viridis or H. fusca.

Examine a living hydra with the naked eye or with a pocket lens, and note the
cylindrical body with one end attached by means of a disc (foot), and the other
surrounded by long active tentacles six to ten in number. Observe that the body
changes its form, being sometimes elongated with all the tentacles extended, while
at other times it is contracted to form a short thick column with the tentacles re-
duced to rounded nobs. Observe, further, that when elongated, the tentacles move
about apparently in search of food, and that when small crustacea, &c., are secured
they are conveyed to the oral aperture situated in the centre of the oral cone. If
there are any buds present, note what stage of growth they have reached.

A. Place a living specimen in a watch glass in a drop of water and examine with
a low power, noting again the body, tentacles, oral cone, foot, and buds if pre-
sent, and also—

1. That the mouth leads into a central cavity, which, though closed posteriorly,
extends into the tentacles, into which food particles freely enter.

2, That the walls of the body and tentacles consist of two layers, an outer layer
(ectoderm), and an inner layer (endoderm), which in H. viridis contains
chlorophyll granules.

3. The genital sacs, if present, the testes projecting from the body immediately
behind the tentacles, and the ovaries from the body near its base.

B. Make a sketch showing the hydra in an extended and in a contracted state,
and indicate in the latter sketch all the structures referred to above.
10

C, Place on a glass slip and examine with a high power, noting—

1. The large ectoderm neuro-muscular cells, with their nuclei, and the processes
which form the fibrillated layer between the ectoderm and endoderm.

2, The small interstitial cells lying between the large ectoderm cells,

3. The threadcells (nematocysts), some with the thread still coiled up within
the sac, and others with the thread everted. Observe that some of the
threads are short, while others are long, and that some of the long threads
have three short barbs at their base. If the threads are not visible, a.
drop of acetic acid usually leads to their eversion.

4. The endoderm cells forming a single layer with delicate processes (cilia) pro-
jecting into the body cavity, and with food particles and vacuoles scattered
through the protoplasm, and in H. viridis with, in addition, chlorophyll
granules.

5. A testis, which when flattened by pressure on the cover glass, is seen to
contain ripe or developing spermatozoa. The ripe sperms consist of a
head and of a long motile filament, while the developing sperms may either
be—(1) in the form of small round granular or hyaline ectoderm cells; or
(2) small oval cells with a process growing out from one end to form
the filament.

6. An ovary which may contain—(a) a number of small round cells; (0), a
large round nucleated cell, surrounded by small cells; (c) a ripe ovuam,—
a large irregular-shaped amoeba-like cell, with a distinct germinal vesicle
and a germinal spot ; or (d), an ovum in process of segmentation enclosed
in a thick capsule.

D, Indicate in an ideal transverse section the ectoderm cells with their thread
cells and processes, the interstitial cells between them, and the endoderm
cells, with their cilia, vacuoles and granules lying within the fibrillated layer.
Indicate also the various stages seen in the development of the spermatozoa
and ova, and a segmented ovum if present, within its capsule.

Advanced Students should make and examine transverse sections of the body
and tentacles of hardened specimens, in order to study and draw the ectoderm and
endoderm cells, their various processes, and the nematocysts.
THE EARTHWORM; Lumbricus terrestris.

Observe in a living earthworm the natural movements, and the rows of sete
which subserve locomotion—the four rows of sete are easily detected by carrying
the finger along the ventral surface from behind forwards ; the dark dorsal and pale
ventral surface and the iridescent cuticle; the clitellum; the small retractile lobe
(prostomium) in front of the mouth and the numerous rings (somites) between the
mouth and the terminal anal segment.

A, Make a sketch (2 nat. size) of the dorsal surface of the first 40 or 50
segments showing—
(a) The prostomium.
(6) The enlarged segments (29 to 36 inclusive) which form the clitellum.
(c) The dorsal vessel (if visible) running along the median line and the
position of the single row of minute dorsal pores.

B, Make a similar sketch of the ventral surface showing—

(a) The mouth between the prostomium and the 1st segment.

(b) The 8 setz in each segment (except Ist, 2d, 3d, and last)—2 ventral
and 2 lateral on each side of the median line.

(c) The clitellum.

(d) The thickening of the epidermis in the region of the inner setiger-
ous glands (8th to 11th segments).

(e) The 4 apertures of the spermathecae—two on each side—between the
9th and 10th and 10th and 11th segments.

(f) The genital openings between the ventral and lateral seta, (1) of the
2 oviducts in the 14th segment and (2) of the vasa deferentia in
the 15th segment.

(g) The openings of the segmental organs (nephridia), some internal
and others external, to the ventral sete,—nephridia absent from
1st and 2d segments. :
14

C, Fix the earthworm with the dorsal surface upwards by one pin through the
Ist, and another through the 50th segment, and cover with salt solution.
Cut along the middle line from the 25th to the Ist segment, and fix back
the skin by introducing pins obliquely through the 3d, 7th, 12th, 16th and
20th segments.

Observe and indicate in a drawing (2 nat. size)—

(a) The mesenteries (intersegmental muscular septa), and the segmental
organs in connection with them.

(b) The supra-cesophageal nerve ganglia (3d segment).

(c) The pharynx (Ist to 7th segments) cesophagus (8th to 15th segments),
and the calcareous cesophageal glands, proventriculus-(16th to 17th),
gizzard (18th), and the intestine, invested with buff-coloured pig-
ment, extending backwards from the 19th segment.

(d) The bilobed anterior and the usually simple posterior seminal vesicles
(9th to 12th seginents).

(e) The two pairs of spermathece,

(f) The dorsal vessel above the intestine, breaking up into a plexus over
the pharynx, and the dilated lateral vessels arching round the
intestine from the 8th to the 15th segments.

D. With a pair of fine scissors remove one of the segmental organs. Mount in
salt solution, and examine first with low and then with high power, noting
and drawing—

(a) The ciliated funnel-shaped opening by which the segmental tube
communicates with the body cavity (ccelom), in front of the
mesentery.

(0) The narrow portion which pierces the mesentery.

(c) The coiled glandular portion behind the mesentery lined with ciliated
epithelium, and surrounded by capillaries in connection with the
dorsal and sub-intestinal blood vessels.

E, Examine in salt solution, first with low and then with high power, a portion
of a seminal vesicle. Note and draw—
(a) Sperm-polyplasts in various stages of development.
(b) Free spermatozoa—usually better seen in contents of spermathece.

F, In the same preparation look for and sketch, if present, the following stages
in the life history of the gregarina of the earthworm (Monocystis lumbrici).
(a) Free gregarine.
(6) Cysts containing—
(1) Two entire gregarinz or a single gregarina.
(2) Gregarine partly broken up.
(3) Pseudo-navicule.
16

G. After turning the right seminal vesicles to one side and observing the three
cesophageal calcareous glands (12th and 13th segments); the lateral blood
vessels joining the sub-intestinal vessel; and the pharyngeal plexus formed by
the breaking up of the longitudinal vessels ; carefully turn aside the portion
of the alimentary canal exposed, and fix to the left of the middle line.

1. Examine the nervous system, noting the small nerves running forwards
from the supra-cesophageal ganglia towards the prostomium, the
lateral commissures passing downwards to the ventral nerve-cord, so
as to complete the nerve ring, and the ventral cord formed by a pair
of fused ganglia in each segment from the fourth backwards connected
by a pair of united commissural cords.

2, Continue the examination of the genital organs, noting at each side of
the nerve-cord—

(a) The two pairs of spermathecee (between the 9th and 10th,
10th and 11th segments).

(b) The two small ovaries (one near each side of nerve-cord in 13th
segment).

(c) The oviducts which open internally in 13th segment, and exter-
nally through 14th segment.

(d) The two pairs of small testes (front of 10th and 11th
segments), and the seminal ducts which have four rosette-shaped
ciliated internal openings (two in the 10th and two in the
11th segment), and two external openings in the 15th
segment,—testes only visible when seminal vesicles are small.

3. Make an enlarged drawing (4 nat. size) shewing the genital organs and
the exposed portion of the nervous system,

H. Remove the ovary and oviduct from one side, and examine with low power
in salt solution.
(1) Sketch the pear-shaped ovary and the ripe and unripe ova in its
interior.
(2) Sketch the trumpet-shaped oviducts indicating their wide ciliated
internal openings into which the ova find their way on escaping
from the ovary.
18

I, Cut along the middle line from the 25th to the 40th segment, and after fixing
the skin at each side, examine the blood vessels. Make a diagram shewing,
in a side’ view, the dorsal, sub-intestinal, latero-neural, and sub-neural trunks,
and the lateral branches connecting the dorsal with the sub-intestinal, and
the dorsal and sub-intestinal with the sub-neural. Remove the worm
from the salt solution and continue the incision along the middle line.

(a) Collect and examine (high power) the perivisceral fluid, noting and
drawing the granular amceboid corpuscles.

(6) Cut across the dorsal vessel and examine the blood (high power),
noting and drawing the small oval colourless blood corpuscles.

(c) Strip off a small portion of the cuticle from the middle line of the
back and examine (high power), noting the row of comparatively
large dorsal pores, and the extremely small canals scattered
irregularly over the surface, and the fine lines which cause the
iridescence.

(d) Examine the sete from various segments (low power), noting and
drawing the modified forms in the region of the clitellum, and in the
10th, 15th, and 23d segments.

J. Examine a prepared transverse section of earthworm—
1. With low power; note and draw—

(1) The body wall consisting of (a) the structureless cuticle, (b) the epi-
dermis, (c) a pigmented circular muscular layer, (d) a longitudinal
muscular layer divided by the setee into four broad and four extremely
narrow bands, (e) the parietal layer of ccelomic epithelium.

(2) A mesentery (if present) extending between the body wall and the
intestine.

(3) The alimentary canal, indicating (a) the pigmented visceral layer of
the ccelomic epithelium, (0) the longitudinal muscular layer, (c) the
circular muscular layer, (d) the typhlosole and its blood vessel, (e) the
dorsal and sub-intestinal blood vessels, and the lateral vessels if pre-
sent.

(4) The nerve cord, and the three vessels in connection with it.

(5) The setze (two lateral and two ventral on each side), the muscles ex-
tending from their inner ends to the body wall, and the setigerous
glands between the muscular bands.

(6) The segmental organs and their apertures internal or external to the
ventral sete.

2. With high power ; draw a portion to show—

(1) The nucleated cells of the epidermis.

(2) Circular and longitudinal muscular fibres of the body wall and intestine.

(3) The long granular cells of the visceral layer of the ccelomic epithelium
and the ciliated nucleated cells of the intestinal epithelium.

(4) The muscular fibres and epithelium of the mesentry, if visible.

(5) The nerve cord which consists of (a) a muscular sheath, in connection
with which are three large fibres, (b) nerve fibres, especially abun-
dant in the centre and on the dorsal aspect, and of (c) ganglionic cells,
which in the ganglia occupy the ventral surface and sides.

Advanced students may further examine the epithelium covering the various organs
and lining the body cavity, and the blood vessels in preparations, made from
the tissues of a fresh earthworm, treated with } p.c. solution of silver nitrate,
and mounted in glycerine.
20

THE MEDICINAL LEECH; Hirudo medicinalis.
A. Natural Movements.

Observe that the leech crawls by fixing the anterior sucker as far as possible
ahead of the posterior, and then after detaching the posterior sucker by shorten-
ing itself, it brings the posterior sucker to within a short distance of the anterior, the
posterior having been fixed, the anterior is then detached, and the process repeated.
When ascending a vertical surface, note that the body is thrown into a loop by the
posterior sucker being fixed immediately behind the anterior. Observe further,
that it sometimes completely detaches itself, and after assuming a ribbon-like form
swims along in an undulating manner with the dorsal surface upwards when
moving in a vertical direction, but with one of the margins usually upwards when
moving in a horizontal direction.

B. External Characters.

Note—
1. The dark olive colour of the slightly convex dorsal surface, and at each side
of the middle line (a) an orange band, (6) a similar band interrupted
by dark elongated spots, (c) a dark, narrow band bordered with orange

on the one side and with yellow on the other.

2. On the flattened ventral surface a number of dark patches scattered irregu-
larly over a pale olive ground between two broad dark bands.

3. That the body is made up of a large number of rings, and that the Ist,
2nd, 3rd, 5th, and 8th rings are in some leeches provided with a pair
of simple eyes arranged around the anterior end; from the presence of
eyes it may be inferred that the 1st and 2nd rings represent the Ist and 2nd
segments, the 3rd and 4th, the 3rd segment; and that the 5th, 6th, and
7th rings represent the 4th segment; the segments between the 4th and
the posterior sucker are probably made up of 5 rings each, the posterior
sucker seems to consist of 7 segments.

4. The anterior sucker formed by the upper lip projecting backwards at each
side of the mouth, and the large posterior sucker with the anus lying
between its dorsal margin and the last ring—apply the anterior sucker to
the skin, and note the presence of the three toothed ridges.

5. On the ventral surface, the penis in the centre of the 24th ring behind the
mouth, and the female genital opening between the 29th and 30th rings,
the openings, if visible, of the large mucous glands of the 39th, 40th, and
41st rings, and the small apertures of the segmental organs on every 5th
ring.

Make a sketch of the dorsal and another of the ventral surface to show
the external characters.

~
22

C. Dissection.

The leech having been killed with chloroform, should be fixed under water, and
an incision carried along the dorsal surface from the third to the second last ring.
The skin should then be carefully reflected and fixed with pins at each side of the
middle line, in order to expose the alimentary canal and its appendages. In doing
this, note the dorsal and the lateral blood vessels and the absence of a distinct body
cavity.

1 mints and draw the digestive tract, indicating—

(1) The thick-walled tubular pharynx connected by muscular fibres to
the body wall.

(2) The thin-walled stemach with 11 pairs of saccular diverticula (which
correspond to the ganglia of the nerve-cord from the 4th to the
14th inclusive), and that the 11th pair of diverticula send long

. projections backwards towards the end of the body.

(3) The small tubular intestine running along between the projection of
the 11th pair of diverticula to dilate slightly before opening to the
exterior between the last ring and the upper margin of the posterior
sucker.

2. Indicate in the same sketch, the position of the dorsal and lateral blood

vessels—the remains of the reduced body cavity.

3. Examine (high power) the blood (which is coloured with hemoglobin) for the

colourless corpuscles.

4, Make an incision along the pharynx, stomach, and intestine, and note—

(1) The position of the circular muscles which on contraction close both
ends of the fusiform cavity, and the muscles which radiate to the
skin, and serve for producing the sucking action, and also the longi-
tudinal folds containing muscular fibres which serve for driving the
blood backwards into the gastric diverticula. :

(2) That the stomach is constricted by incomplete septa, which, extend
inwards between the diverticula, and that communicating by a small
aperture with the pharynx in front, it projects slightly into the in-
testine behind.

(3) That the gastric diverticula consist of a small anterior and of a larger
posterior chamber, the posterior chamber of the 11th extending, as
already seen, nearly to the end of the body.
24

5. Cut across the pharynx near its centre, and the intestine near its termina-
tion, and carefully remove the intestinal tract, in order to expose the blood
vessels, nervous system, and the reproductive and segmental organs.

Observe—

(1) The ventral blood vessel enclosing the nerve cord and sending branches
to communicate with the lateral blood vessels.

(2) The segmental organs (17 pairs corresponding to the 2d to the 18th
ganglia inclusive) consisting of convoluted tubes in connection with
rounded vesicles.

(3) The 9 pairs of testes (corresponding to ganglia 8 to 16 inclusive) with
their ducts opening into the two vasa deferentia, and that the vasa
deferentia become convoluted to form the large vesicule seminalis
which communicate with the penis—the penis lies in a bent sheath
which, springing from a large sac, opens through the 24th ring behind
the mouth.

(4) The 2 small ovaries lying in the segment behind the vesicule seminalis,
which communicate by slightly twisted oviducts with a muscular
uterus—the uterus opening to the exterior between 29th and 30th
rings behind the mouth.

(5) The 4 mucous glands, if visible, lying behind the ovaries.

(6) The nerve cord extending backwards from the cesophageal ring to end
in a large ganglion lying above the posterior sucker. Noting—

(a) The two supra-cesophageal ganglia giving off 5 pairs of optic
nerves and communicating with the 3 small buccal ganglia
which lie one above and one at each side of the buccal cavity.

(b) The commissures connecting the supra-cesophageal ganglia with
the sub-cesophageal ganglion, which is made up by the fusion
of 3 or 4 embryonic ganglia, and from which several (4) pairs
of nerves extend to the surrounding tissues.

(c) The 2d to the 21st post oral ganglia, each giving off 2 pairs of
nerves, the 22d ganglion giving off only 1 pair of nerves, and
the 23d (made up of 6 or 7 embryonic ganglia) giving off 7
pairs of nerves.

(7) Examine with a low power and sketch a portion of the double nerve
cord lying in the ventral blood vessel, and one of the ganglia with
its lateral branches.

(8) Make a drawing, showing (a) the ventral and lateral blood vessels, (b)
the nephridia, (c) the generative organs and the nervous system.
26

6. Examine the buccal cavity, noting the Y-shaped oral aperture, and the
toothed ridges which lie on the inner surface of the three lobes formed
by the strong buccal muscles.

7. Remove one of the toothed ridges, examine (low power), and sketch.

8. Advanced students should prepare and

(1) Examine (low power), and afterwards sketch transverse sections—

(i) Through the middle of the body, showing (a) cuticle ; (0) epider-
mis and dermis, containing capillaries and simple glands ; (c)
external circular, longitudinal, internal circular, radiating and
dorso-ventral muscular fibres; dorsal, lateral, and ventral blood
vessels; and the nerve cord or ganglia ; (d) the stomach and its
diverticula ; (¢) the nephridia, testes, and vasa deferentia.

(ii) Through the anterior end of the body, noting (a) the ocelli,
closed capsules containing large -transparent cells; (6) the
nerve cells of the supra-cesophageal ganglia ; (c) the cup-shaped
glands in the epidermis.

(2) Examine (high power) (a) one of the ovaries teased in salt solution,
and sketch several ova; (b) one of the testes prepared in the same
way, and draw the spermatozoa; (c) one of the ganglia teased in
carmine or picro-carmine, and sketch the ganglion cells.
28

THE STAR-FISH ; Asterias rubens.

Observe in the living star-fish the natural movements. Notice that locomotion is
effected by the pedicels or tube feet on the under (oral) surface of the rays, these
pedicels having suckers at their tips, whilst the terminal pedicels of the rays are
unprovided with suckers, and act as tentacles.

Turn the star-fish on its aboral surface and observe how it twists round the tip of
one or more of its rays until the pedicels situated there can be attached, the pedicels
further back being then applied by a similar and progressive twisting of the ray,
until by this spiral-like movement the disc is drawn over.

A. Make a sketch (natural size) of the slightly convex aboral surface, showing the
central pentagonal disc with the five rays radiating from it; the whitish circular
madreporic tubercle placed towards one side of the disc and opposite the point of
junction of the two rays which form the biviwm; the minute anal opening placed
slightly to the left of an imaginary line from the tubercle to the tip of the
opposite ray; the calcareous ossicles bearing short spines embedded in the soft
tissue of the integument, and the short stems bearing pincer-like heads—the
pedicellarias.

Remove one of these pedicellariz, examine with low power and draw.

B, Sketch the flat oral surface, showing—
(a) The large central mouth.
(b) The five ambulacral grooves running along the oral faces of the rays.
(c) The two double rows of pedicels nearly filling these grooves.
(d) At the tip of each ray the small red eye spot.

C. 1. Remove and examine under low power one of the pedicels, noting the sucker-
like tip strengthened by five or six calcareous plates,
2, Examine also a pedicel from the tip of the ray, and notice that it is not
terminated by a sucker.
3. Pull off carefully the pedicels from a portion of one of the rays, and notice
the radial nerve extending along the centre of the ambulacral groove to
end in the eye-spot.
30

D. Fix the star-fish, mouth downwards, under water. Select the ray furthest
from the madreporic tubercle, and cut through the skin along each side of the ray
from the base to the tip; dissect off this strip of skin, and make a drawing of the
organs exposed, viz. :—

(a) The two large brown sacculated hepatic ceca lying along nearly the whole
length of the ray on each side of the ambulacral plates ;—notice that near
the base of the ray each cecum ends in a delicate tube; and that the
two tubes unite to form a single hepatic duct which opens into the large
‘membraneous pyloric sac of the stomach.

(b) The stomach, with its eversible cardiac pouches projecting into each ray
below the hepatic duct ; ;

(c) The two reproductive glands, the duct from each passing into the side of the
inter-radial partitions, where it joins with that from the next ray to open to
the exterior in the angle between the rays.

BE. Reflect the skin from the central disc, taking care not to injure the madre-
poric tubercle, and sketch—
(a) The stomach, with its cardiac and pyloric sacs.
(b) The short intestine near its centre.
(c) The rectal glands opening into the intestine.
(d) The retractor muscles of the cardiac pouches.
(¢) The short cesophagus.

F, Remove the pyloric ceca and reproductive organs carefully from the dissected
ray, and examine and sketch the ampulle of the pedicels. Scrape off some of
these, and notice that the pores for the pedicels are placed between the ambulacral
ossicles and alternately near the base and near the ridge, appearing to be in two
rows though forming only a single irregular one.

G. Cut transversely through the ray, and sketch—

(a) The ambulacral ossicles sloping up to meet in a ridge at the centre, and
forming the ambulacral groove.

(b) The small plates—interambulacral plates—on which they rest.

(c) The inter-radial septa formed by junction of the inter-ambulacral plates of
adjacent rays.

(d) The cut section of the radial water tube lying below the ridge formed by
the ambulacral plates.

(e) The radial blood-vessel lying below the water-vessel.

(f) The radial nerve lying external to the blood-vessel.

Dissect out carefully the stone canal which extends from the madreporic
tubercle to the circum-oral water tube ; trace one of the radial water vessels to the
ring, and notice the sinus running parallel to the stone canal, and opening into a
circular vessel beneath the water ring, from which spring the radial blood-vessels.
32

THE SEA URCHIN; Lchinus esculentus.

A. Observe the natural movements of the living animal, noticing that it uses for
locomotion not only the pedicels or tube feet, like the star fish, but also the spines
which cover the test ; and that on a flat surface it uses its teeth also for this purpose,
by projecting them and pushing itself over them. Touch any part of the test, and
observe that the adjacent spines and pedicellarie all converge to the point of stimu-
lation, the pedicellarize attempting to grasp the irritating object.

B. Make a drawing of the sea urchin from the side, indicating :—The spheroidal
form; the small tubercles bearing movable spines; the five ambulacral areas per-
forated for the pedicels, and the five inter-ambulacral areas between them. Notice
that the ambulacral areas are wide where they commence at the mouth, and
narrow towards the aboral region. ,

C. Scrape off the spines from a small portion of both areas, and sketch—

(a) The double row of plates in each area bearing the tubercles, which are of
various sizes, and bear corresponding sized spines.

(b) The perforations in the ambulacral plates for the pedicels.

D. Scrape off a few of the spines in the aboral region, and indicate the arrange-
ment of the plates exposed :—

(a) The five genital plates perforated for the genital ducts, one of them larger
and rougher than the others serving as the madreporic tubercle.

(b) The five smaller ocular plates placed between the genitals—one at the apex
of each ambulacral area.

(c) The central semi-nfembraneous area surrounded by the genital plates, and
perforated by the anal opening.

E. Sketch the oral surface, showing the large membraneous area with the mouth,
occupied by the five teeth in the centre; and the five pairs of tentacles projecting
from the sinuses which surround the lantern.

F. Remove, examine (low power), and draw the following structures :-—

(a) One of the spines, indicating its fluted appearance and the cup or socket
at its base surmounted by a ridge with muscular fibres adhering, which
held the spine in contact with the tubercle on the surface of the test.

(b) Several of the pedicellarize,—noting that they consist of a long slender stem,
partly calcareous and partly membraneous, and of a head made up of three
movable mandibles.

(c) One of the pedicels with its sucker-like tip containing five or six calcareous
plates.
G. Cut with a pair of scissors round the “equator line” of the echinus, and
separate the two halves without tearing across the intestine, and lay the upper
portion beside the lower with aboral surface downwards. Make a sketch
showing—

(a) The dentary apparatus, or Aristotle’s Lantern.

(6) The alimentary canal passing from the lantern and coiling round the test,

to terminate in the centre of the aboral region.

(c) The generative organs hanging in lobes from the test around the anal aper-

ture, and opening by five ducts to the exterior.

(d) The stone canal which passes from the madreporic tubercle in a direct central

line to end in the water ring surrounding the cesophagus.

(e) The polian vesicles,

(f) The five radial water vessels which pass down outside the alveoli to reach

the ambulacral area.

(g) The pedicels springing from the radial vessel, and the ampulle formed on the

tube which projects into the test from the bases of the pedicels.

(hk) The membraneous sinus which runs alongside the upper part of stone canal.

H. Sketch the dentary apparatus in position from the side and from above,
showing—

(a) The five pairs of long triangular alveoli connected by interalveolar muscles.

\b) The teeth Tying between the alveoli. .

(c) The radii extending across the base of the lantern.

(d) The rotule articulating at their outer ends with the alveoli, and at their inner
with the radii.

(e) The transverse muscles connecting the radii.

(f) The protractor muscles extending from the top of each alveolus to the inter-
ambulacral areas.

(g) The retractor muscles extending from the oral ends of the alveoli to the auricles.

I. Cut away carefully with scissors the tips of the alveoli on one side of the
lantern, to expose the pentagonal ridge, which forms the nerve ring, on the inner
surface of the oral membrane. Trace the radial nerves from the nerve pentagon
along the ambulacral areas to their termination in the eye-spots on the ocular plates.

J. Remove a portion of the nerve cord and examine with the microscope (low
power), noting the lateral branches, and also the radial water vessel and its lateral
prolongations.
UNIVERSITY OF EDINBURGH
ZOOLOGICAL LABORATORY.

THE DISSECTION

THE SKATE.

BY

J. COSSAR EWART, MD,
REGIUS PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF EDINBURGH,

AND

J. DUNCAN MATTHEWS,

DEMONSTRATOR OF ZOOLOGY IN THE UNIVERSITY OF EDINBURGH.

 

EDINBURGH:
JAMES THIN, PUBLISHER TO THE UNIVERSITY.
1885.
THE SKATE. Rava batis or Raia clavata.

Examine the living skate in an aquarium, and note that it swims in an undulating |
manner principally by the action of the large pectoral fins, that in breathing the
water enters by the mouth and the two spiracular apertures, and after passing over
the gills, escapes through the gill slits, and also by the spiracular apertures; note
also that in breathing the spiracles and gills beat rhythmically from 30 to 32 times
per minute, and that the mouth sometimes opens and closes at the same rate.

A. External characters—
1, Examine the skate, noting—
(a) The rhomboidal form, and that it is depressed from above downwards.
(6) The colour—dark dorsally and ventrally in FR. batis, dark dorsally, white
ventrally in R. clavata.
(ce) The thick skin—smooth in R. batis, rough in R. clavata, owing to the
presence of small denticles (placoid scales).
(d) The large dermal denticles scattered more or less over the dorsal and ventral
surfaces of R. clavata, but only along the dorsal surface of tail of R. batis.
(e) The delicate sensory tubes beneath the skin, and their numerous external
apertures (best seen in R. batts).
(f) The anterior projecting rostrum.
(g) The large triangular-shaped pectoral fins.
(A) The smaller bi-lobed pelvic fins.
(t) The long narrow tail with its terminal caudal fin.
(j) The pair of elongated claspers (in the male only).
2. Make a sketch of the dorsal and ventral aspects, indicating as far as possible
the above characters ; and also—
(1) In the dorsal view—

(a) The oval-shaped depressed eyes.

(6) The spiracular apertures, spiracular cartilages, and pseudo-branchie.

(c) The minute apertures of the aqueducti vestibuli at the posterior end
of the head.

(d) The pair of dorsal fins.

(2) In the ventral view—

(a) The large mouth with its upper and lower jaws covered with flat
enamelled teeth (generally raised into sharp ridges in male of R.
clavata).

(b) The ae apertures, connected by the naso-buccal grooves with the
mouth.

(c) The fronto-nasal process—the fold of integument between the naso-
buccal grooves. :

(d) The ten gill clefts arranged in two semi-circular rows, and behind
the last gill openings a pair of slit-like markings resembling a sixth
pair of clefts,

(e) The ridges formed by the pectoral and pelvic girdles.

(f) The large cloacal aperture.

(g) The pair of small abdominal pores posterior to it,

3. Cut out and sketch one of the large denticles, noticing that it consists of a
flattened bony base buried in the integument and a projecting sharp
enamelled spine.
B. Alimentary system.

1. Cut away the whole of the ventral wall of the abdomen between the pectoral
and pelvic girdles, noting—

(a) The skin.

(b) The muscles.

(c) The internal peritoneal lining.

2. Sketch the viscera thus exposed, in situ, indicating—

(a) The tri-lobed liver.

(6) The stomach.

(c) The large intestine (colon).

(d) The rectum and rectal gland.

Note also the red lobulated spleen.

3. Turn forwards the liver, and note in addition to the above—

(a) The duodenum.

(b) The pale bi-lobed pancreas.

(c) The gastro-hepatic and the duodeno-hepatic omenta between the liver and
the stomach and the liver and the duodenum respectively.

(d) The gastro-splenic omentum attaching the spleen to the dorsal surface of
the stomach.

(e) The mesogaster and mesorectum suspending the stomach and rectum
respectively from the dorsal wall of the abdomen.

4, Examine the liver, noting—

(a) Its division into three lobes,

(b) The gall bladder between the right and middle lobes.

(c) The short cystic duct from the gall bladder, the two hepatic ducts, one
from the right lobe, the other from the middle and left lobes, and the
common bile duct into which they open,—trace the bile duct to the point
where it opens into the duodenum.

5. Examine the pancreas and the pancreatic duct. Trace the duct to the
duodenum into which it opens opposite the aperture of the bile duct.

6. Cut out the liver, and ligature the alimentary canal in front of the stomach,
and behind the rectal gland; cut through the mesenteric attachments and
remove the whole alimentary tract. Make a sketch of the part of the alimen-
tary tract removed, and indicate the position of the pancreas and the pan-
creatic and bile ducts,

7. Cut open the stomach and duodenum, and note the pyloric valve between
them, and the longitudinal folds of the mucous membrane of the stomach.

8. Wash out the colon, noting the external spiral line indicating the attachment
of the valve inside. Fill the colon with air by a blow-pipe, and tie at each

end: allow to dry for some days, and then cut apertures so as to examine
further the arrangement of the spiral valve.
C. The reproductive and excretory systems.
1. Of the male.

(a) Examine and sketch—

(1) The pair of testes,—smooth on ventral, lobulated on dorsal surface.

(2) The much-coiled epididymes,—note the narrow connection between
the testes and epididymes.

(8) The coiled vasa deferentia (barely visible in young fish) terminating
in an enlarged portion, the seminal vesicle.

(4) The sperm sac lying external to the seminal vesicle.

(5) The pair of elongated lobed kidneys on each side of the posterior
part of the vertebral column, and external to the peritoneum, by
which they are covered.

(b) Remove the pelvic girdle (for future examination) without injury to the
cloacal chamber. Cut open the cloaca, and note-the large anal aperture
and the median urino-genital papilla.

(c) Carefully cut along the papilla and expose the urino-genital sinus, and note
in it the apertures of the ureters and of the sperm sacs.

(d) Insert a bristle into each of these apertures, then remove the thick peri-
toneum covering the kidneys, and note the ureters running along the
inner edge of the kidneys and communicating with them by numerous
efferent ducts, also the yellow inter-renal bodies situated between the
ureters and kidneys.

(e) Cut open one of the sperm sacs, and note at its neck the aperture of the
seminal vesicle.

(f) Examine (high power) the contents of the sperm sac, and sketch a sperma-
tozoon, noting its twisted elongated head and the long tail.

2. Of the female.

(a) Examine and sketch—

(1) The ovaries,

(2) The anterior portions of the oviducts, noting that the right and
left unite in the middle line on the ventral aspect of the cesophagus,
and open into the abdominal cavity by a single median aperture,

(3) The rounded oviducal gland, the secretion of which forms the case
or “purse” for the ovum.

(4) The posterior portion of the oviducts.

(5) The kidneys.

(6) The bi-lobed urinary bladder.

(7) The delicate mesonephric ducts running forwards from the bladder.

(6) Carefully remove the pelvic girdle without injuring the cloaca, dissect
off the peritoneum from the kidneys, and note the ureters on their inner
edge, and the yellowish inter-renal bodies.

(c) Cut open the cloaca and note the apertures of the rectum and oviducts, and
the central small urinary papilla.

(d) Insert a blowpipe through the urinary papilla and inflate the bi-lobed
bladder. Cut it open and note the minute apertures of the ureters,
D. Prepare the skeleton of the skate,
1, The skull, note—

(a) The four labial cartilages on each side, the first supporting the lateral flap
of the fronto-nasal process, the second on the outer margin of the naso-
buccal groove, the third forming the internal, and the fourth the external
margin of the nasal aperture.

(6) The flat floor of the skull. ;

(c) The roof, with the anterior and posterior fontanelles.

(d) The foramen magnum.

(e) The two rounded occipital condyles.

(/) The indentation for the odontoid process of the vertebral plate.

(g) The anterior projecting rostrum.

(h) The pair of rostral cartilages at the sides of the rostrum.

(zt) The nasal capsules.

(4) The auditory capsules.

(&) The following apertures on one side—

(1) In the region of the eye a large aperture for the optic nerve.

(2) Some minute apertures over the optic foramen for the passage of 4th
nerve,

(3) Behind the optic foramen a small aperture for 3rd nerve.

(4) Anterior to the auditory capsule the aperture for 7th nerve.

(5) Above and anterior to (4) the aperture of 5th nerve.

(6) In the lower posterior part of the auditory capsule, the aperture for
10th nerve.

(7) External to (6) the aperture of 9th nerve.

(8) Two apertures in the nasal capsule for the passage of the orbito-nasal
and the palato-nasal divisions of 5th nerve.

(9) On the surface of the posterior part of skull the apertures of the
aqueducti vestibuli.

Make a sketch of the skull from above, from below, and from the side.
2. The jaws and branchial arches, note—

(a) The upper jaw (palato-pterygoid arch).

(b) The lower jaw (mandibular arch).

(c) The hyomandibular cartilage connecting the jaws to the lower portion of
the auditory capsule.

(d) The small spiracular cartilage (metapterygoid) between the hyomandibular
cartilage and the auditory capsule.

(e) The hyoid arch articulating with the hyomandibular, and composed of a
dorsal epihyal, a median ceratohyal, and a ventral small hypohyal
segment.

(f) The five branchial arches composed of (from above downwards) pharyngo-,
epi-, cerato- and hypo- branchial portions,—note that the hypobranchial
portions of the first branchial arch meet in the middle line, to form a
narrow bar slightly behind the lower jaw ; that the hypobranchials of the
fifth arch meet in the middle line to form a large basibranchial plate
with a pair of anterior horns; and that the pharyngobranchials of the
fourth and fifth arches unite with each other.

Note the pair of elongated thymus glands lying dorsal to the pharyngo-
branchials.

Make a sketch showing the jaws and branchial arches from below.

3. The pectoral girdle and pectoral fins, note—

(a) That the two sides unite in the middle line forming a bar—the coracoid
portion of the girdle—across the body on the ventral surface.

(b) The two halves on the dorsal surface, forming the scapular portions of the
girdle. :

(c) The small supra-scapular portions, forming the attachment of the girdle to
the vertebral plate.

(d@) The three glenoid facets on each external édge of the girdle, which form
articulating surfaces for the fins.

(e) The three fontanelles on each side.

(f) The three divisions of each fin, viz.—

(1) The long propterygium, articulating with the anterior glenoid facet,
and composed of several pieces, one of which reaches the antorbital
cartilage.

(2) The small mesopterygium articulating with the middle glenoid facet.

(3) The long metapterygium, which consists of several pieces, and
articulates with the posterior glenoid facet.

(g) The long jointed cartilaginous fin rays.

Sketch the pectoral girdle and one of the fins.
10

2. The jaws and branchial arches, note—

(a) The upper jaw (palato-pterygoid arch).

(b) The lower jaw (mandibular arch).

(c) The hyomandibular cartilage connecting the jaws to the lower portion of
the auditory capsule.

(d) The small spiracular cartilage (metapterygoid) between the hyomandibular
cartilage and the auditory capsule.

(e) The hyoid arch articulating with the hyomandibular, and composed of a
dorsal epihyal, a median ceratohyal, and a ventral small hypohyal
segment.

(f) The five branchial arches composed of (from above downwards) pharyngo-,
epi-, cerato- and hypo- branchial portions,—note that the hypobranchial
portions of the first branchial arch meet in the middle line, to form a
narrow bar slightly behind the lower jaw ; that the hypobranchials of the
fifth arch meet in the middle line to form a large basibranchial plate
with a pair of anterior horns; and that the pharyngobranchials of the
fourth and fifth arches unite with each other.

Note the pair of elongated thymus glands lying dorsal to the pharyngo-
branchials.

Make a sketch showing the jaws and branchial arches from below.

3. The pectoral girdle and pectoral fins, note—

(a) That the two sides unite in the middle line forming a bar—the coracoid
portion of the girdle—across the body on the ventral surface.

(b) The two halves on the dorsal surface, forming the scapular portions of the
girdle. ;

(c) The small supra-scapular portions, forming the attachment of the girdle to
the vertebral plate.

(d) The three glenoid facets on each external édge of the girdle, which form
articulating surfaces for the fins.

(e) The three fontanelles on each side.

(f) The three divisions of each fin, viz.—

(1) The long propterygium, articulating with the anterior glenoid facet,
and composed of several pieces, one of which reaches the antorbital
cartilage.

(2) The small mesopterygium articulating with the middle glenoid facet.

(3) The long metapterygium, which consists of several pieces, and
articulates with the posterior glenoid facet.

(g) The long jointed cartilaginous fin rays.

Sketch the pectoral girdle and one of the fins.
12

4. The pelvic girdle and pelvic fins (already detached). Note—

(a) That it consists of a bar (pubis) with small anterior and posterior projecting
processes—the prepubic and iliac processes.

(b) The anterior and posterior lobes of the fin, and the two acetabular facets.

(c) The fin rays of the anterior lobe of fin attached directly to the pelvic
girdle—the anterior (preaxial) ray being much thicker than the others.

(d) The basipterygial portion of fin supporting the fin rays which form the
posterior lobe—observe that it is divided into several pieces, which in the
male are connected with the sharp cartilages of the clasper.

Sketch the pelvic girdle and one of the fins.

Examine a clasper, noting the groove along its edge and the form of the cartilages.

5. The vertebral column, note—

(a) The unsegmented anterior vertebral plate.

(b) The odontoid process at its anterior end.

(¢) The two articulating surfaces for the condyles of the skull.

(d@) The free vertebree forming the remainder of the column.

(e) The fin rays of the dorsal fins attached to basal pieces.

6. Make transverse and longitudinal sections through—

(a) The vertebral plate, noting the flat ventral surface, the lateral and dorsal
ridges, and the neural canal.

(b) The vertebrae immediately behind the vertebral plate, noting—

(1) The partially ossified bi-concave centra.

(2) The transverse processes bearing small cartilaginous nodules (rudi
mentary ribs).

(3) The neural and interneural processes.

(4) The neural spine.

(5) The neural canal, formed by the neural processes and spine.

(6) The soft remains of the primitive notochord filling the spaces between
adjacent vertebra.

(c) The caudal vertebrae, noting—

(1) The centrum.
(2) The neural processes,
(3) The neural spine.
(4) The neural canal.
(5) The hemal processes.
(6) The heemal spine.
(7) The hemal canal.
(8) The remains of the notochord.
Make a sketch of the vertebral column complete, and of the transverse and longi-
tudinal sections examined.
14

Second State.

Examine the arteries and veins described under I, 1 and 2, p. 20, and after re-
moval of the alimentary canal and liver as described above, examine—

E. The nervous system.

Remove the roof of the skull and the upper part of the anterior vertebral plate, so
as to expose the brain and a portion of the spinal cord, taking care to leave
uninjured the eye and ear of the left side.

1. Note—

(a) The gelatinous matter contained in the anterior portion of the cranial
cavity.

(b) The arachnoid fluid.

(c) The dura mater lining the cartilaginous walls of the cavity.

(d) The pia mater enveloping the brain and spinal cord.

2. Make a sketch (2 nat. size) of the dorsal surface of the brain, etc., indicating—

(a) The elongated olfactory nerves.

(6) The fused cerebral lobes.

(c) The optic thalami.

(d) The pineal gland (lying on the optic thalami).

(e) The rounded optic lobes.

(f) The elongated cerebellum, its anterior and posterior lobes marked by eleva-
tions (gyri) and depressions (sulci).

(g) The medulla oblongata and the convoluted corpora restiformia which form
part of the medulla and lie on each side of the cerebellum.

(h) The spinal cord which is divided by fissures into a pair of dorsal and a pair
of ventral columns.

(«) The cranial and spinal nerves within the cavity of the skull and vertebral
column.

3. Carefully make out the distribution of the cranial nerves :—

I. The large olfactory nerve springing from the cerebral lobe and passing for-
wards to enter the nasal capsule, where it forms a cylindrical band, from
which small branches pass to the transverse folds of the nasal mucous
membrane.

II. The optic nerves forming the optic chiasma and passing outwards through
the optic foramina to enter the eye-balls.

III. The oculo-motor arising from the crura cerebri and passing outwards and
forwards to supply the superior and internal recti muscles of the eye,
and then downwards to the inferior rectus and inferior oblique muscles.

IV. The pathetic arising from the anterior region of the cerebellum and
supplying the superior oblique muscle of the eye.
16

V. The trigeminal arising in conjunction with the 7th and 8th nerves from the
medulla and dividing into three branches :—

(a) The first branch,—orbito-nasal,—consisting of a dorsal division which
passes forwards over the muscles of the eye, and a ventral which
passes over the external rectus, but under the superior and internal
recti and superior oblique, to meet and unite with the dorsal branch—
the common trunk then passes to the nasal capsule, within which it
divides into two branches, one running transversely over the nasal
sac, while the other passes forwards to the rostrum to supply the
gelatinous tissue, etc., in the anterior region of the head.

(b) The second branch runs forwards external to the orbito-nasal and
divides into two branches—(1) the palato-nasal which passes beneath
the muscles of the eye to supply the ventral parts of the rostrum,
fronto-nasal process, etc.; and (2) the maxillary which supplies the
upper jaw, antorbital cartilage, etc.

(ce) The third branch—mandibular—which runs forwards parallel to the
maxillary nerve, and supplies the mandible and part of the upper jaw.

VI. The abducens leaving the skull, close to the 5th and 7th nerves, to
supply the external rectus muscle of the eye.

VII. The facial, which, after passing through its foramen in the skull, divides
into two branches—(a) the palatine nerve, which passes in front of the
spiracle to supply the pseudo-branchiz and mucous membrane of mouth;
(6) the hyomandibular, which passes outwards in front of the auditory
capsule to be distributed over the hyomandibular cartilage, jaw muscles,
etc., and supply small branches (chorda tympani) to the mandible,

VIII. The auditory entering the anterior part of auditory capsule to send
branches to the vestibule and ampulle.

IX. The glossopharyngeal passing obliquely through the ventral portion of
auditory capsule to be distributed round the first gill cleft (hyoid half-gill
and anterior half-gill of first branchial arch.)

X. The vagus passing backwards close to the auditory capsule and along the
anterior vertebral plate to send four branches to the gills of the four posterior
gill clefts, and then dividing into a ventral (gastric and cardiac) branch,
and a lateral branch which supplies the sensory tubes, etc.

Make a sketch showing the distribution of the cranial nerves.

4, Examine the spinal nerves; observe that each arises by two roots which pass
separately through the wall of the spinal column to unite outside; note
that the first 16 nerves of each side unite to form the brachial plexus which
gives off branches to the pectoral fin, while the remainder supply the various
parts of the body walls, fins, etc.
18

5. Cut through the spinal cord behind the medulla, and the cranial nerves within
the skull; carefully remove the brain with the handle of a scalpel, and
examine and sketch the ventral surface, indicating—

(a) The cerebral hemispheres.

(6) Optic chiasma.

(c) Lobi inferiores beneath the optic thalami.

(d) Pituitary body (hypophysis cerebri) and infundibulum.

(e) The three lobed saccus vasculosus.

) The crura cerebri and the anterior portion of the medulla oblongata.

6. Lift up the cerebellum and note the cavity of the 4th ventricle covered by a
delicate vascular membrane. Note between the optic thalami, and covered by
the pia mater, the cavity of the 3rd ventricle. Cut open the optic lobes
and mesencephalon to expose the aqueductus Sylvii connecting the 3rd and
4th ventricles.

7. Cut across the cerebral hemispheres, and note that there are no lateral ven-
tricles.

F. Examine the eye of the left side.

1. Note its external characters, viz. :—

(a) Its elongated and depressed form.

(b) The absence of eyelids.

(c) The cornea forming the front of the eyeball.

(d) The pupil.

(e) The pigmented iris, with a fringe hanging downwards from its upper
margin.

2. Dissect off the skin and note—-

(a) The cartilaginous sclerotic covering the posterior two-thirds of the eye and
continuous with

(6) The transparent cornea covering the anterior portion.

(c) The superior oblique muscle attached to the upper anterior portion of the
eyeball, and passing to the anterior part of the orbital cavity.

(d) The superior rectus muscle attached to the upper posterior portion of the
eye.

(e) The internal rectus muscle immediately in front of the superior rectus,
passing beneath the superior oblique, and: attached to the anterior portion
of the eye.

(f) The external rectus muscle attached to the posterior part of the eye and to
the orbital cavity immediately behind the superior rectus. ,

(g) The inferior oblique muscle attached to the lower anterior portion of the eye.

(h) The inferior rectus muscle inserted into the lower portion of the eye.

(4) The cartilaginous peduncle articulated by its inner end to the skull and
by its outer to the eyeball.

Make a sketch of the eyeball with the muscles attached.

3. Cut open the eye transversely near the junction of the sclerotic and cornea,
and note—

(a) The aqueous humour between the iris and cornea.

(6) The crystalline lens,

(¢) The black choroid coat lining the interior surface of the sclerotic.

(d) The iris continuous with the choroid and the aperture (pupil) in its
centre.

(e) The vitreous humour filling the posterior chamber of the eye.

(f) The retina lying within the choroid and covering the posterior portion of
the eye.

Make a sketch showing an ideal section of the eye.
20

G. Cut open the nasal sac and note the folds formed by the mucous membrane; the
folds lie parallel to each other and at right angles to a longitudinal median
ridge.

H. Carefully cut away from above, in thin slices, the cartilage of the left auditory
capsule, and expose the membranous labyrinth, noting—

(a) The large rounded vestibule with its two depressions filled with endo-
lymph.

(b) The suaiiootas vestibuli leading upwards from the vestibule to the exterior.

(c) The anterior and posterior, and the lateral horizontal semicircular canals,
and the three ampulle.

(d) The large soft otolith lying in the vestibule.

Note the distribution of the VIIIth. nerve to the vestibule and ampulle.

Make a diagram showing the vestibule, semi-circular canals, and the aqueduct.

I, Circulatory system.

1. Remove the abdominal wall to expose the viscera, slightly stretch the
mesenteric membranes, and note—

(a) The portal vein in the duodeno- hepatic omentum, —observe that it is formed
by the gastric, duodenal, intestinal, splenic and pancreatic veins, and
that it passes to the middle lobe of ‘liver, giving off branches to the right
and left lobes.

(b) The cceliac artery arising from the aorta, on the dorsal side of the ceso-
phagus, and dividing into gastric, hepatic, and duodenal arteries.

(c) The superior mesenteric artery, arising from the aorta posterior to the cceliac,
and dividing into intestinal, splenic, and pancreatic arteries.

Mark these arteries by inserting bristles, and then cut out the liver to within half
an inch of its anterior end, so as not to i injure the hepatic sinus (for descrip-
tion see 10, p. 22), or the alimentary canal.

2, Examine (low ‘and high power) a drop of the blood, noting the large oval
nucleated red corpuscles, and the smaller multi-nuclear white corpuscles.

3. Remove the ventral wall of the pericardial chamber in front of the pectoral
girdle within the line of the branchial clefts, noting the pericardium and
the pericardial fluid and the opening, in the middle line, of the pericardial
chamber which leads into the two canals (pericardio-peritoneal) that bring
the pericardium into communication with the abdominal cavity.

4, Examine the heart, noting—

(a) The semicircular sinus venosus.

(6) The thin-walled auricle.

(c) The thick muscular ventricle.

(d) The pylangium (conus arteriosus), extending forwards from the ventricle.
(e) The synangium (bulbus arteriosus), anterior to the pylangium.
22

_ 5." Dissect out—

‘oasnaia (a) The ventral aorta, passing forwards from the synangium.

(6) The right and left posterior innominate arteries, arising from the root of
the ventral aorta—trace them and note that they each divide into three
afferent branchial arteries for the lamellae of the three posterior gill clefts.

(c) The right and left anterior innominate arteries, arising from the anterior end
of the ventral aorta,—note that each divides into two afferent branchial
arteries for the lamellae of the first and second gill clefts.

Note the red coloured thyroid gland situated at the anterior end of the ventral
aorta. Make a sketch of the heart and afferent branchial vessels.

6. Carefully expose the gill chambers, and note the hypo-branchial artery crossing
the afferent branchial arteries, internal to the gills. Arising from the hypo-
branchial artery are the anterior and posterior coronary arteries.

7. Note that the gill sacs are completely separated from each other by fibrous septa,
extending from the outer borders of the arches, and that the septa are sup-
ported by cartilaginous rays. Observe that the gill lamellae are attached
along their whole length to the septa.

8. Turn the heart forwards and examine the sinus venosus. Insert a bristle or
probe into the sinus, and then slit it open. Note that the bristle has passed
into the Cuvierian sinus.

9. Carefully cut away the part of the pectoral girdle over the sinus, and examine
the venous system, noting the apertures in the Ouvierian sinus of the
anterior and posterior cardinal veins, the brachial vein, the hepatic sinus,
and on the dorsal side the chief lymphatic trunk.

10. Pass a bristle along the hepatic sinus, and note that the sinus communicates
at each end with a Cuvierian sinus, and receives the hepatic veins from the
liver.

11. Pass a bristle along the posterior cardinal veins or inflate with a blow-
pipe, and note that the right and left communicate with a median (cardinal)
sinus near the centre of the abdominal cavity. From this sinus they pass
backwards separately to the posterior end of body.

12. Trace the brachial veins along the margin of abdominal cavity, and note
the branches joining them from the pectoral fins. Look for the femoral and
iliac veins, and observe, that having united, they again separate into an outer
branch (epigastric) which joins the brachial, and an inner branch (ileo-
haemorrhoidal) which enters the cardinal sinus.

13. Note that the caudal vein from the tail divides into two renal portal veins
which break up in the kidneys.
24

14. Cut away the basi-branchial plate on the floor of the mouth; carefully
dissect off the mucous membrane from the roof of the mouth, and examine
the efferent branchial arteries.

Observe that the efferent branchial arteries unite to form the dorsal aorta. Note

(a) That the two branches from the lamelle of the Ist gill cleft unite with two
branches from the lamelle of the 2nd gill cleft to form the first efferent
artery.

(b) That ihe two branches from the 3d gill cleft form the second efferent artery.

(c) That the third efferent artery is formed of three branches—two from the
4th and one from the 5th gill cleft.

15. Note—

(a) The vertebral arteries springing from the 1st pair of efferent arteries and
passing through the anterior vertebral plate to the brain and spinal cord.

(6) The common carotid arteries arising from the anterior branch of the first
efferent arteries just before they emerge from the first gill cleft, Trace
them forwards, and note that each gives off a small spiracular artery, and
then bifurcates to form

(1) An external carotid supplying the jaws, etc.

(2) An internal carotid—the right and left internal carotids meet in
middle line and pass through a foramen in the floor of the skull
to supply the brain, etc.

(ec) The brachial arteries springing from the aorta in front of the third efferent
arteries.

16. Trace the dorsal aorta backwards, and note—

(a) The origins of the cceliac and superior mesenteric arteries.

(6) The spermatic arteries supplying the testes (ovarian if a female).

(c) The inferior mesenteric artery supplying the rectum and rectal gland.

(d) The renal arteries supplying the kidneys.

(e) The iliac arteries.

(f) The continuation of the aorta along the hemal canal of the vertebral
column as the caudal artery.

17. Slit up the conus arteriosus, and note the three longitudinal rows of valves,
each row consisting of five semi-lunar valves, the fifth valve of each row being
largest.

18. Carefully remove the heart, including the sinus venosus, from the pericardial
chamber, cut open the auricle and ventricle, and note—

(a) The delicate walls of the auricle.

(6) The thick walls of the ventricle and the muscular columne carne
strengthening them.

(c) The large aperture between the sinus venosus and the auricle, and the
two folds forming the sinu-auricular valve.

(@) The two folds forming the valve of the auriculo-ventricular aperture—look
for the small cusps in the triangular spaces left between the large folds,

J. The sympathetic nervous system.

1. Note the series of sympathetic ganglia running along each side of the
vertebral column (a large ganglion lies close to the inner side of each
Cuvierian sinus). Observe that the ganglia are connected by commissures
to each other, and to the cerebro-spinal nerves,
UNIVERSITY OF EDINBURGH
ZOOLOGICAL LABORATORY.

 

DISSECTION

THE RABBIT.

BY
J. COSSAR EWART, MD.,
REGIUS PROFESSOR OF NATURAL HISTORY, UNIVERSITY OF EDINBURGH,
AND

WILLIAM SMITH,

DEMONSTRATOR OF ZOOLOGY, UNIVERSITY OF EDINBURGH,

 

EDINBURGH:

JAMES THIN, PUBLISHER TO THE UNIVERSITY.
1888.
THE RABBIT; Lepus cuniculus.

A. External characters. Observe—
1. The head, consisting of a rounded cranial portion, and an elongated facial
portion.

(a) The mouth, a small transverse aperture on the under surface of the
front of the head, bounded by the upper and lower lips.

(b) The external nostrils or anterior nares, a pair of oblique slits at the
fore end of the snout, connected with the mouth by a median hair-
less groove.

(c) The vibrissz, long stout hairs on the upper lip.

(d) The eyes, each protected by an upper and a lower eyelid, and by a
third eyelid or nictitating membrane, formed by a fold of opaque
white skin that can be pulled across the eye from its inner corner.

(e) The large movable external ears, each supported at its base by
cartilage.

2. The trunk, made up of two portions; the anterior portion or thorax,
and the posterior portion or abdomen.

(a) The anus, with at each side a hairless patch, the perineal space, on
which the ducts of the perinzal glands open.

(b) The urinogenital opening, in front of the anus; in the male, small
and situated at the end of the penis, which is loosely covered by
a sheath, the prepuce; in the female, large and slit-like.

(c) In the adult male, the scrotal sacs, into which the testes descend,
two ovoid pouches of skin, one on either side of the root of the
penis.

(d) In the female, the teats, four or five pairs of small projections,
the anterior pair being thoracic in position, the remaining three
pairs abdominal.

3. The short tail.
4, The limbs.

(1) The fore-limb, consisting of—

(a) The upper arm or brachium, closely applied to the side of the
thorax, and enclosed in the skin of the trunk.

(Lb) The fore-arm or anti-brachium.

(c) The hand or manus, provided with five clawed digits, and hav-
ing its palmar surface covered with hair. The innermost
digit, the pollex, is the shortest, and does not reach the
ground.

(2) The hind-limb, much longer that the fore-limb, and divided into—

(a) The thigh or femur, which is inclosed in the skin of the trunk.
(b) The leg or crus.

(c) The foot or pes, which is very long, and provided with four
clawed digits—the first digit or hallux being absent. Its
sole, or plantar surface, is covered with hair.

B, The Abdominal Viscera.

Fix the animal with its ventral surface upwards. Make an incision through
the skin over the sternum, and continue it forwards to the mandibular symphysis,
and backwards to the pubic symphysis. Dissect carefully the skin from the
underlying parts.

Note the panniculus carnosus, a thin sheet of muscle covering the whgle
ventral surface of the trunk and neck; and in the female the mammary glands
with their ducts passing to the teats.

Open the abdomen by a mesial incision from the posterior end of the
sternum to the symphysis pubis. From this make transverse cuts on either
side along the margin of the ribs. Pin out the flaps and note the following
viscera in position.

(a) The liver, a large dark red body, consisting of several lobes.

(b) The stomach, immediately behind the liver and partly covered by it.

(c) The duodenum, long and narrow.

(d) The small intestine, long, narrow, reddish, and much coiled.

(e) The cecum, wide, dark in colour, coiled, and marked by a spiral
constriction, and ending in the vermiform appendix.

(f) The colon, with sacculated walls, lying between the folds of the
cecum.

(g) The rectum.

(h) The urinary bladder, in front of the symphysis pubis.

Observe that the peritoneum lines the body cavity, and invests, or

extends over, its various contents.
Turn the alimentary tract aside in order to expose the following
parts :-—

(<) The spleen, an elongated dark red body behind the stomach, and
attached to its cardiac end by the gastro-splenic omentum.

(j) The kidneys, lying behind the peritoneum and attached to the dorsal
wall of the abdomen, the right one being the more anterior.

(k) The adrenal bodies, small, round, yellowish structures, one near the
inner margin of each kidney.

(1) The diaphragm, a muscular partition separating the thorax from the
abdomen.

(m) The mesentery, a double fold of peritoneum supporting the alimen-
tary canal.

(n) The celiac ganglia, situated in the mesentery, opposite the right
adrenal body.
6

C, Dissection of the Alimentary System. “Note—

1.

2.

3.

4.

5.
6.
7.
8. The colon, with its rows of sacculations.
9.

The stomach.

Turn the liver forwards and observe the dilated cardiac end, and
the end of the cesophagus; the narrow pyloric end; and the
greater and lesser curvatures.

The duodenum, running from the pylorus along the right side of the
abdomen posteriorly and returning to form a long U-shaped loop.
The pancreas, (seen on turning the duodenum over to the left side),
consisting of a number of fatty-looking lobules scattered in the

mesentery of the duodenal loop.

The pancreatic duct receiving smaller ducts, and opening into
the ascending limb of the duodenum: an accessory duct opens into
the upper end of the duodenum.

The liver, its convex anterior surface applied to the diaphragm, and
attached to it by the suspensory ligament, its concave posterior
surface applied to the stomach; its five lobes, viz. :—

(a) The left central lobe, lying against the left half of the
- diaphragm.

(b) The left lateral lobe, largest in size and partially sub-divided,

lying between the left central lobe and the stomach.

(c) The right central lobe, lying against the right half of the dia-

phragm, and grooved on its posterior surface for the gall-bladder.

(d) The caudate lobe, closely applied to the right kidney.

(e) The Spigelian lobe, smallest in size, and fitting into the lesser

curvature of the stomach.

The gall-bladder, elongated, thin-walled, dark green or brown in
colour, embedded in the right central lobe of the liver.

The bile-duct, running from the small end of the gall-bladder to
open into the duodenum immediately beyond the pylorus. It
receives hepatic ducts from the various lobes of the liver.

The small intestine, continuous with the duodenum.

The sacculus rotundus, the dilated end of the small intestine open-
ing into the side of the caecum.

The cecum and vermiform appendix.

The rectum, terminating in the anus.

General structure of the alimentary canal.

1.

The stomach. Tie a ligature round the esophagus near its entrance
to the stomach, and another round the duodenum an inch beyond
the pylorus. Remove the stomach from the body ; slit it up along
its posterior aspect; wash it, and note—

(a) The external serous coat, bluish-white and glistening.

(6) The middle muscular coat, thickened towards the pylorus.

(c) The internal mucous coat, with prominent ruge.

(d) The pyloric valve, and the opening of the bile duct.
8

2. The small intestine. Prepare and examine a piece. Note—

(a) The villi, minute processes of the mucous membrane.

(b) Peyer’s patches, of a honey-combed appearance, occurring at
intervals along the whole length of the small intestine on its free
margin.

3. The cecum. Remove it from the body; slit it open longitudinally,
and note——

(1) The internal papillose surface.

(2) The prominent spiral fold.

(3) The openings of the sacculus rotundus and the colon.

(4) The inner surface of the vermiform appendix, similar to a Peyer’s
patch.

4. The colon. Slit it open; note the papillose surface and the saccula-
tions.
5. The rectum. Note its smooth mucous lining.

DP, The Thoracic Viscera.
Open the thorax by a longitudinal incision on each side of the sternum,
and remove the sternum with the attached portions of ribs.
Note the following parts in position—

1. The thymus gland, variable in size, in the anterior part of the thorax.

2. The heart and pericardium.

3. The lungs, trachea, and bronchii, the left lung divided into two lobes,
the right into four. Inflate the lungs from the trachea.

4. The diaphragm, with its central tendon and its two posterior muscular
crura.

5. The phrenic nerves, lying between the heart and the lungs, and divid-
ing posteriorly to supply the diaphragm.

6. The pleure, lining the cavity of the thorax and reflected over the
lungs, forming two sacs, one on each side with a space between (the
mediastinum).

7. The csophagus, running in front of the back bone and piercing
the diaphragm.

EE, The Circulatory System. :
Remove the thymus gland, expose the heart and the roots of the great vessels.
The heart and great vessels. Note —~
1. The heart, conical in form, with its apex or ventricular portion
directed backwards and to the left, and its base or auricular portion
forwards.
(a) The left ventricle, forming the apex and left side of the ventricular
portion.
(6) The right ventricle, forming the right side of the ventricular
portion, but not reaching to the apex.
10

(ec) The right auricle, dorsal in. position to the base of the right
ventricle with an auricular appendix.
(d) The left auricle, anterior to the left ventricle, with an auricular
appendix.
2. The great vessels.
(a) Vessels opening into the right auricle.

(1) The right superior vena cava, running along the inner side
of the right lung, to open on the dorsal wall of the right
auricle.

(2) The left superior vena cava, running along the inner side
of the left lung, to open into the left side of the right
auricle.

(3) The inferior vena cava, piercing the diaphragm and running
forwards, a little to the right of the middle line of the body,
to open into the posterior end of the right auricle.

(b) Vessels arising from the right ventricle.

(1) The pulmonary artery, arising from the anterior border of the
right ventricle and arching over to the dorsal surface of the
left auricle, where it divides into right and left pulmonary
arteries.

(c) Vessels opening into the left auricle.

(1) The pulmonary veins, opening on the dorsal surface of the
left ventricle.

(d) Vessels arising from the left ventricle.

(1) The aorta, arising from the middle of the base of the heart
behind the root of the pulmonary artery, running forwards,
then arching over to the left side, and descending at the left
side of the vertebral column. The ductus arteriosus, an
obliterated vessel connecting the aorta with the pulmonary
artery.

The veins.
1. The system of the vene cave.
(a) The right superior vena cava formed by—

(1) The right subclavian vein, from the fore-limb and shoulder.

(2) The right external jugular vein, from the side of the neck,
formed by the union of the anterior and posterior facial veins.

(3) The right internal jugular vein, close to the trachea,
joining the external jugular vein at its point of union with
the subelavian.

(4) The vena azygos, lying close to the vertebral column on the right
side of the aorta, and passing round the right side of the
cesophagus and trachea to join the vena cava close to the
auricle. It receives seven or eight pairs of intercostal veins.

(5) The anterior phrenic vein, passing forwards from the diaphragm
along the inferior vena cava,
12

(6) The right anterior intercostal vein, joining the vena cava just
in front of the vena azygos.

(7) The right internal mammary vein, from the inner surface of
the ventral thoracic wall, joining the vena cava at the level of
the first rib.

(b) The left anterior vena cava, differing from the right only in so far
as it receives no azygos vein, and has a different course in order to
reach the heart.

(c) The posterior vena cava, running forwards through the liver dor-
sally, to pierce the central tendon of the diaphragm, and open
into the right auricle. Note the following veins joining it—

(1) The posterior phrenic veins, from the diaphragm.

(2) The hepatic veins, generally four in number, joining the
inferior vena cava in the liver substance.

(8) The renal veins, (one pair), from the kidneys, Each receives
a small vein from the adrenal body, and one from the dorsal
wall of the abdomen.

(4) The spermatic veins (ovarian in the female), (one pair), from
the testes (or ovaries).

(5) The ilio-lumbar veins, (one pair), from the hinder part of the
abdominal walls.

(6) The external iliac veins, (one pair), direct continuations of the
femoral veins from the thigh.

(7) The internal iliac veins, (one pair), running through the pelvis
from the dorsal aspect of the thighs.

2. The portal system. Observe the portal vein lying close to the posterior
vena cava, and dividing to supply the various lobes of the liver. It is
formed by the junction of—

(1) The lieno-gastric from the walls of the stomach and the spleen.

(2) The duodenal, from the duodenum and the pancreas.

(3) The anterior mesenteric, carrying blood from the small intes-
tine, caecum, colon, and rectum.

(4) The posterior mesenteric, from the rectum.

The pulmonary system. (See above, p. 10, 2, (c).)

The arteries.

1. The aorta. Trace this artery along its whole length, noting the
following branches —
(a) The innominate artery, from the arch of the aorta dividing into—

(1) The right subclavian artery, running on as the brachial artery
and giving off the vertebral and the internal mammary
arteries.

(2) The right carotid artery, dividing into the inter al and the
external carotid arteries.

(b) The left carotid artery, dividing into the left internal and the
external carotid arteries.
14

(c) The left subclavian artery, corresponding in its distribution to the

right subclavian artery.

(d) The intercostal arteries, (several pairs of small arteries).

(e) The celiac artery, dividing into the hepatic artery and the lieno-

intestinal artery.

(f) The anterior mesenteric artery, dividing into numerous branches.

(g) The renal arteries, passing each to the hilum of a kidney.

_ (h) The spermatic or ovarian arteries.

(7) The posterior mesenteric artery.

(j) The lumbar arteries.

(k) The median sacral artery.

(1) The common iliac arteries, formed by the bifurcation of the aorta,
running to the hind limbs as the femoral arteries. Each gives
off in the abdomen—

(1) The ilio-lumbar artery.
(2) The internal iliac artery, and
(3) The vesical artery.
The pulmonary artery. (Sce above, p. 10, 2, (b).)

F. Dissection of the Heart.
Remove the heart from the body by cutting through the gre&t vessels about
half an inch from the heart.
1. The auricles. Expose the cavities of both auricles by cutting away their
outer walls.
(1) The right auricle. Note the thin wall, thicker in the appendix,
and marked by muscular ridges ; note also—

(a) The openings of the three vene cave.

(b) The Eustachian valve between the openings of the left superior
vena cava and the inferior vena cava.

(c) The septum auricularum with the fossa ovalis.

(d) The right auriculo-ventricular opening.

(2) The left auricle. Note the thin wall, thicker in the appendix.

(a) The openings of the pulmonary veins.

(b) The left auriculo-ventricular opening.

(c) The coronary sinus (the dilated portion of the coronary vein),
embedded in the posterior wall of the left auricle.

2. The ventricles.

Make a transverse section of the ventricles, about one third of an inch from
the apex. Note the shape of the cavities of the ventricles and the relative
thickness of their walls.

(1) The right ventrical. Remove its outer wall, and note—

(a) The tricuspid valve of the right auriculo-ventricular opening,
formed of three membranous flaps attached to its margin ;
the chord tendinez passing from these flaps to the muscular
processes of the walls of the ventricle.
16
(b) The opening into the pulmonary artery, guarded by three semi-
lunar cusps.
(2) The left ventricle. Remove its outer wall, and note—

' (a) The mitral valve (bicuspid) of the left auriculo-ventricular
opening, corresponding in structure to the tricuspid valve, but
with larger musculi papillares,

(b) The muscular ridges of the wall of the ventricle (columne
carnez).
(c) The opening into the aorta guarded by three semilunar valves.
[Note also the opening of the coronary arteries. |

G, Dissection of the Urinary and Reproductive Systems.
The male rabbit.

1. The urinary system. Examine one of the kidneys, noting (1) its
ovoid shape ; (2) the hilum, or point of entrance of the vessels and
ureter, Make a longitudinal section, and note—

(a) The cortical substance forming the outer layer.

(b) The medullary substance.

(c) The pyramids, conical papille.

(d) The pelvis, or expanded anterior end of the ureter.

Trace the ureter from the kidney to the bladder. Note the general form
and the thin wall of the bladder.

2, The reproductive system. Open the scrotal sacs along their ventral

surface. Note—

(a) The testes, with the spermatic veins and arteries entering at
their anterior ends.

(b) The epididymes, masses of convoluted tubes lying along the inner
border of the testes.

(c) The vasa deferentia, a pair of whitish tubes extending from the
epididymes, to enter the abdominal cavity where, after looping
round the ureters, they reach the neck of the bladder.

Inflate the bladder and the urino-genital canal, from the urethra: remove
the symphysis pubis by cutting through the bones about a quarter of
an inch from the middle line: detach the two crura penis from the
ischia, and make out the following structures—

(a) The urino-genital canal, the continuation posteriorly of the
neck of the bladder.

(b) The penis, with the corpora cavernosa dorsally, and the corpus
spongiosum ventrally pierced by the urethra.

(c) The uterus masculinus, a somewhat bi-lobed median sac
projecting from the dorsal surface of the urino-genital canal.

(d) The openings of the vasa deferentia, on the ventral wall of
the uterus masculinus.

(e) The prostate, a glandular body connected with the neck of the
bladder and the uterus masculinus.
18

(f) Cowper's glands, a pair of brown ovoid masses immediately
behind the prostate.

(g) The rectal glands, a pair of brown bodies about an inch long,
situated on either side of the rectum.

(h) The perineal glands, similar in appearance to the rectal glands
but shorter, situated on either side of the penis. Trace their
ducts to their openings on the perinzal spaces.

Slit up the urethra, and continue the incision along the wall of the
bladder in the middle line. Note—

(a) The openings of the ureters, on the dorsal wall of the bladder.

(b) The verumontanum, a small papilla on the dorsal wall of the
urethra immediately beyond the neck of the bladder.

(c) The opening of the uterus masculinus, on the dorsal wall of
the urethra anteriorly to the verumontanum.

(d) The openings of the prostatic ducts, usually four in number,
at the sides of the verumontanum.

The female rabbit.

1. The urinary system—as in the male, except for the position of the
openings of the ureters into the bladder.

2. The reproductive system. Inflate the bladder and vagina from the
urino-genital opening, and. remove the pubic symphysis by cutting
through the bones about a quarter of an inch from the middle line,
Note—

(a) The clitoris, corresponding in position and structure to the
penis of the male.

(b) The vestibule, or urino-genital canal.

(c) The vagina, running from the neck of the bladder upwards.

(d) The two uteri, opening separately into the vagina.

(e) The Fallopian tubes, continuous with the uteri, and suspended
by folds of peritoneum—the broad ligaments : the fimbriated
ends of the Fallopian tubes lying near the ovaries.

(f) The ovaries, a pair of ovoid bodies attached to the dorsal
wall of the abdomen: the Graafian follicles, small projec-
tions on the surfaces of the ovaries.

(g) Cowper’s glands, on the dorsal wall of the vestibule.

(h) The perineal and rectal glands, similar to those in the male.

H. Dissection of the Head and Neck.

(The following dissection is made chiefly on account of its physiological
importance.)
1, Lay the skin well back on both sides of the neck, and observe the fol-
lowing muscles—
(a) The platysma, a very thin superficial muscle: cut through this longi-
tudinally in the middle line,

(6) The sterno-mastoid, near the middle line, running from the sternum
20

forwards and outwards, crossing below the jugular vein, to the
mastoid process of the skull.

(c) The sterno-hyoid, nearer the middle line, running from the sternum
to be attached to the inner third of the cornu majus of the hyoid
bone.

(d) The sterno-thyroid, below, and external to, the sterno-hyoid, run-
ning from the sternum to the lower border of the thyroid
cartilage of the larynx.

(e) The thyro-hyoid, running from the thyroid cartilage to the hyoid bone.

(f) The stylo-hyoid, running from the tip of the cornu majus of the
hyoid to the styloid process.

(g) The mandibular muscles.

2. On the right side, carefully raise up the sterno-mastoid muscle along its
inner aspect, and fix the muscle in position with a hook, and observe the
following nerves——

(a) The pneumogastric (vagus), a stout cord running parallel to the
carotid artery. Trace this nerve to its point of emergence. Note
that it gives off—

(1) The superior laryngeal, which crosses the carotid artery on its
dorsal aspect, and goes to the larynx. Very soon after
leaving the pneumogastric it gives off superior cardiac
(cardiac depressor.) ‘Trace this nerve down the neck, lying
alongside the sympathetic, in the connective tissue of the
sheath of the common carotid artery.

(2) The inferior laryngeal (recurrent laryngeal), which passes
round the subclavian artery. (On the left side it passes round
the innominate artery. )

(3) Branches to the heart, Jungs, and cesophagus.

(6) The hypoglossal, seen running parallel to the cornu majus of the
hyoid bone, and passing under the stylo-hyoid muscle and over the
carotid artery. ‘Trace it forwards to the tongue and backwards to
the skull. Note that just before crossing the point of bifurcation
of the carotid it gives off the ramus descendens noni, which crosses
the carotid on its ventral aspect a little way down.

(c) The sympathetic, already seen in connection with the superior
cardiac. ‘Trace it downwards to the inferior cervical ganglion,
a little above the junction of the jugular vein with the superior
vena cava.

(d) The phrenic, already seen between the heart and the lung. (See
above, D. 5.) ‘Trace it forwards to its origin from the fourth
cervical nerve. [It receives a branch also from the fifth and some-
times from the sixth. ]

(«) The spinal accessory, a small nerve emerging from the skull with
the pneumogastric and the glosso-pharyngeal. (Seen on breaking
away the tympanic bulla.)
22

(f) The great auricular, arising from the third cervical nerve, and running
from the under surface of the sterno-mastoid muscle to the ear,
where it divides into two branches.

3. The trachea. Clear away the muscles connected to it and raise it up.
Note its rings of cartilage, incomplete on their dorsal aspect; the
larynx, at its upper extremity; and its bifurcation to form two
bronchi posteriorly. Trace the bronchi to the lungs.

4. The thyroid gland, made up of an elongated lobe on each side of the
trachea below the larynx, connected by the isthmus which lies in
contact with the trachea.

. The larynx, at the upper extremity of the trachea. Observe the following
parts connected with it :—

(a) The epiglottis, at the root of the tongue, forming a covering for the
glottis.

(b) The large thyroid cartilage.

(c) The cricoid cartilage.

Make a longitudinal section in the middle line, and in the interior

of the larynx note—

(d) The arytenoid cartilages, mounted on the posterior portion of the
cricoid.

(¢) The true vocal cords, stretching from the arytenoid cartilages to be
inserted on the inner aspect of the thyroid cartilage.

(f) The false vocal cords, above, and parallel to, the true vocal cords.

(g) The ventricles of the larynx, shallow pockets between these.

(kh) The glottis, the opening between the vocal cords.

6. Cut through the symphysis of the lower jaw, and remove the left half of
the jaw from its articulation with the skull. Dissect out the paired
salivary glands. Note—

(a) The parotid, a large gland, underneath, and in front of, the outer ear:
trace its duct (Stenson’s) from the anterior part of the gland to
its opening in the cheek near the second upper premolar tooth.

(b) The sub-maxillary, a more compact gland, near the angle of the jaw
and internal to the parotid. Trace its duct (Wharton’s) from the
posterior portion of the gland to its opening on the floor of the
mouth between the lower incisors and the root of the tongue.

(c) The sub-lingual, an elongated gland, lying along the inner border of
the ramus of the jaw. It has many ducts opening singly.

(d) The infra-orbital gland, found just above the zygoma. Trace it
downwards underneath the zygomatic arch, and observe its duct
opening far back in the mouth.

7. Examine the buccal cavity, and note-—

(a) The roof of the mouth, formed of the transversely corrugated hard
palate and the smooth soft palate. Observe the teeth (to be
afterwards studied) ; the naso-palatine canals, two small apertures
behind the second incisor teeth ; and the tonsils, near the termi-
nation of the soft palate.

Or
24

(b) The floor of the mouth. Obscrve the tongue, attached to the floor
of the mouth, with the papille foliate, a pair of oval patches
opposite the last molar teeth, and the circumvallate papille, a
pair of small white papille, a little above and behind the papille
foliatee. Note also the teeth, and the inner aspects of the cheeks,
smooth except for a hairy patch on each,

(c) The pharynx, the posterior portion of the buccal cavity communi-
cating with the mouth, nasal chamber, cesophagus, and _ glottis.
Remove the soft palate, and observe on the inner aspect of a bony
process of the skull, in the position of the back of the soft palate,
the paired valve-like openings of the Eustachian tubes.

I. The Skeleton of the Rabbit.
The vertebral column.

Note the following regions, each distinguished by certain peculiarities
in the vertebree (1) cervical, or neck region; (2) thoracic, or
chest region; (3) lumbar, or loin region; (4) sacral region ;
and (5) caudal, or tail region.

Examine a typical vertebra, say the third lumbar, and note—

(a) The body or centrum, the epiphysial plates and inter-verte-
bral discs, and on its ventral aspect a descending process
(hypapophysis).

(L) The neural arch, composed of two halves springing from
the back of the centrum, each made up of an anterior part
or pedicle, and a posterior part or lamina.

(c) The processes springing from the arch.

(1) The spinous process, projecting backwards from the
junction of the two laminee.

(2) The transverse processes, projecting outwards, one
on each side of the arch.

(3) The articular processes, projecting two anteriorly and
two posteriorly from the junction of the pedicle with
the lamina,

(4) The accessory processes, one on each side of the
hinder end of the neural arch.

(d) The notches, situated one on the upper, the other on the lower
border of each pedicle, and forming, when the vertebre are
joined, the intervertebral foramina.

1. The cervical vertebre.
(a) Examine the seven vertebre of the neck, noting the following common
characters—

(1) The shortness of the centra.

(2) The small size of their spinous processes.

(3) The perforated transverse processes.

(b) Examine the first vertebra or atlas, noting—
26

(1) The absence of a centrum.

(2) The large canal divided into two parts by a transverse
ligament.

(3) The broad horizontal transverse processes.

(4) The anterior articular facets deeply concave for articulating
with the condyles of the skull.

(c) Examine the second vertebrae or axis, and note—

(1) The centrum bearing the odontoid process (body of first
vertebra). '

(2) The spinous process, large and bifid.

(3) The small transverse processes.

(d) Examine the five remaining cervical vertebra, noting—

(1) The form of the centra, and the facets upon the posterior
end of the centrum of the seventh vertebra for the heads
of the first pair of ribs.

(2) The small spinous processes, except in the seventh vertebra.

(3) The broad inferior lamelle of the transverse processes, except
in the seventh.

2. The thoracic vertebre.
(a) Examine the vertebre of the thoracic region, twelve, sometimes
thirteen, in number, and note—

(1) The long slender spinous processes.

(2) On the centra, anteriorly and posteriorly, except in the case
of last three or four vertebre, the facets for the heads
of the ribs.

(3) The transverse processes, with articular facets on their under
surfaces for the tubercles of the ribs, except in the last
three or four vertebre.

(4) The hypapophyses, beginning at the ninth thoracic vertebra,
and increasing in size from the vertebra backwards,

(5) The notches, forming the foramina for the spinal nerves.

3. The lumbar vertebre, usually seven in number. (See above, J.)
Note in addition—

(a) Their large size relative to the other vertebrae.

(b) The strongly developed processes, especially the transverse
processes.

(c) The short stout centrum of the last vertebra.

4. The sacral vertebrae. Note—
(a) That these are four in number, and are fused.
(b) That only the first of these directly supports the pelvis by its
large broad expansion.
. The caudal vertebra. Note—
(a) These are about sixteen in number.
(b) Their processes and arches become reduced posteriorly till
the last vertebrae are represented only by centra.

Or
28

The ribs and sternum.
1. The Ribs. (a) Examine a typical rib (4th or 5th), noting—

(1) The bony vertebral portion, curved above, nearly straight
below; the head of the rib articulating with a facet formed
by the centra of two adjacent vertebree ; the tubercle articu-
lating with the transverse process of the vertebra; and
beyond the tubercle, a small projection for the attachment
of ligaments.

(2) The cartilaginous sternal portion, connecting the vertebral
rib with the sternum.

(Lb) The ribs in general. Note the gradual increase in the length of the
ribs from the first to the sixth, and beyond the sixth the gradual
shortening: beyond the ninth rib the want of tubercles, and the
facets for the head of the ribs confined to one centrum: the sternal
portions of the seven first ribs reaching the sternum, those of the
eighth and ninth connected with the ribs in front of them: the re-
mainder being floating ribs.

2. The sternum. Observe that it is constituted of the following parts.

(a) The manubrium or anterior portion, keeled on its ventral
aspect.

(b) The xiphisternum, or posterior portion, long and slender,
ending bebind in a plate of cartilage.

(ce) Between these, four long portions and one short.

Note the position of the facets for the articulation of the ribs, the first on
the manubrium, the others between the several sternebre.

K. The Skull.
The cranium proper. For the purposes of study, the cranium may be
regarded as composed of certain segments, viz. :—
(a) The occipital segment. Note

(1) The basi-occipital, forming the floor of the hinder end of the
cranial cavity, and bounding the foramen magnum ia front,

(2) The ex-occipitals, bounding the foramen magnum iaterally,
and forming the greater part of the condyles. Nz=te, at the
outer side of each, the long backwardly directed par-occipital
process or paramastoid, closely applied to the tympanic bulla.

(3) The supra-occipital, a large median bone, bounding the
foramen magnum posteriorly.

(b) The parietal segment. Note—

(1) The basi-sphenoid, directly in front of the basi-occipital,
having on its dorsal surface the sella turcica for the lodge-
ment of the pituitary body.

(2) The ali-sphenoids, a pair of wing-like bones fused to the
sides of the basi-sphenoid, and forming part of the floor of
the cranial cavity. From the ventral surface of each there

 
30

projects downwards a vertical plate of bone, the external
pterygoid process, connected along its inner edge with the
palatine bone.

(3) The parietals, meeting at the sagittal suture, and forming a
large part of the roof of the cranial cavity.

(The inter-parietal, a small irregularly lozenge-shaped
bone, lies between the parietals and the supra-occipital.)
(c) The frontal segment. Note—

(1) The pre-sphenoid, a small laterally compressed bone, in
front of the basi-sphenoid, forming the lower margin of the
optic foramen, from which it extends backwards to form
the anterior boundary of the sella turcica, and forwards to
form two thin vertical blades, diverging from each other
to form part of the inner wall of the orbit.

(2) The orbito-sphenoids, a pair of plate-like bones, fused with
the pre-sphenoid, and surrounding the optic foramen, behind
which they form part of the wall of the cranium and of the
orbits.

(3) The frontals, forming the roof and sides of the anterior part
of the cranial cavity, and the upper part of the wall of the
orbit, each bearing a prominent supra-orbital process, and
articulating with each other in the middle line, with the
parietal behind, and with the orbito-sphenoid and_pre-
sphenoid below.

(a) The nasal or olfactory segment. Note—

(1) The mesethmoid, a median vertical plate of cartilage,
extending downwards and forwards in front of the pre-
sphenoid, having its upper and posterior border ossitied and
expanded horizontally to form the perforated cribriform plate.

(2) The nasals, a pair of elongated bones forming the roof of
the nasal cavities, articulating with each other in the
middle line, and with the frontals posteriorly.

(8) The ethmo-turbinals, intricately folded plates of bone, fused
to the lower surface of the cribriform plate.

(4) The maxillo-turbinals, more delicate and more complex bones
attached to the maxille in front of the ethmo-turbinals.

(5) The naso-turbinals, thin bones forming pouches and fused
with the inner surfaces of the nasal bones.

(6) The vomers, a pair of slender plate-like bones fused along
their ventral margins, and embracing the lower edge of the
mes-ethmoid cartilage, and connected posteriorly with the
ethmo-turbinals.

Note the lacrymals, small plate-like bones, indirectly connected with the
nasal capsules. They form part of the anterior walls of the orbits,
and articulate with the frontals aud maxille.
32

The auditory capsules. Note——

(a) The periotics, irregularly shaped bones in the side wall of
the cranium, between the squamosals and the occipital seg-
ment, each consisting of a dense petrous portion, and a
cancellated mastoid portion with a downwardly directed
mastoid process.

(b) The tympanies, in each of which may be recognised a tubular
upper portion (the neck or external auditory meatus), and an
expanded lower portion (the bulla),

(ce) The auditory ossicles, seen on breaking away the outer wall
of the tympanic bone. Observe—

(1) The malleus, with its long process (the manu-
brium) attached to the tympanic membrane.

(2) The incus, articulating with the malleus, and
giving off two processes, the long and short
crura.

(3) The os orbiculare, a small disc of bone attached to
the long crus of the incus.

(4) The stapes, a stirrup-shaped bone articulating
with the os orbiculare, and having its base
inserted into the fenestra ovalis.

Connected with the auditory capsules are the squamosals, a pair of bony
plates in the cranial wall below the parietals, articulating with the
periotics, orbito sphenoids, and ali-sphenoids. Each sends forwards
and outwards a stout zygomatic process to articulate with the jugal
bone.

Dones in connection with the Jaws.
(u) The upper jaw.

(1) The maxille, a pair of large irregular bones, in each of which
the following parts may be distinguished: the body or
alveolar portion, extending backwards into the front part of
the orbit, and inwards to form the transverse palatal process
(part of the hard palate) ; the zygomatic process, prolonged
upwards into the orbital process, which forms the anterior
boundary of the orbit ; the fenestrated facial plate, forming
the lateral Loundary of the olfactory chamber.

(2) The pre-maxille, a pair of bones forming the anterior part
of the upper jaw, articulating with each other in front and
with the maxille behind, and each sending a long, slender
nasal process backwards between the nasal bone and the
maxilla as far as the anterior process of the frontal,

(3) The pterygoids, a pair of narrow vertical plates of bone
attached to the skull at the junction of the alisphenoids
with the basi-sphenoid.

(4) The palatines, a pair of nearly vertical plates of bone, articu-
34

lating with the pre-sphenoid above, the pterygoids and ali-
sphenoids behind, and with the maxille in front.

(5) The jugals, a pair of laterally compressed bones. Hach
jugal articulates with the squamosal, and forms the greater
part of the zygomatic arch, and anteriorly fuses with the
zygomatic process of the maxilla.

(b.) The lower jaw.

(a) The mandible, consisting of a pair of bones, each made up
of a stout horizontal portion bearing the teeth, and a
thinner posterior portion, the angle, from which the ascend-
ing ramus takes rise and ends in the elongated condyle,
which articulates with the under surface of the zygomatic
process of the squamosal.

(b) The hyoid bone, consisting of a median portion or body,
and two pairs of cornua projecting backwards.

The Appendicular Skeleton.
The pectoral girdle.
1. Remove the scapula from its muscular connections, and note—

(a) Its triangular form, the apex directed downwards and forwards, and pro-
viding the glenoid cavity for the head of the humerus,

(b) The spine, running along the outer surface, and ending in the acromion
process, which bears on its posterior surface the long metacromion
process.

(c) The coracoid process, overhanging the glenoid cavity.

2. The clavicle. Note its small size, its slender form, and its position in the
ligament that runs from the scapula to the sternum.

The fore limb.

Remove the muscles from the fore limb, and examine the following parts :—

1, The humerus, an elongated bone, forming the skeleton of the upper arm,
its head articulating with the glenoid cavity of the scapula, its trochlear
end with the supar-trochlear fossa in front, which communicates by the
supra-trochlear foramen, with the olecranon fossa behind.

2. The bones of the fore-arm.

(a) The radius, an elongated, slightly curved bone, lying in front of the ulna
at the elbow joint, but along its inner side at the wrist, articulating
at the elbow with the grooves of the trochlea of the humerus, and
with the anterior surface of the ulna, and at the wrist with the
carpal bones.

(b) The ulna, an elongated bone articulating at the elbow with the humerus
by the sigmoid notch on its enlarged end, and with the radius by two
small surfaces, and at the wrist by its small end with the carpal bones.
Note, behind the elbow joint, the olecranon process of the ulna.

3. The wrist, composed of two rows of carpal bones.

(a) The proximal row, consisting of (1) the scaphoid (radiale) on the
36

inner side, articulating with the radius; (2) the semilunar (inter-
medium), articulating with the radius ; (3) the cuneiform (ulnare), on
the outer side, articulating with the ulna.

(b) The distal row, consisting of (1) the trapezium, on the inner side
articulating with the scaphoid, and supporting the first metacarpal ;
(2) the trapezoid, articulating with the scaphoid and the centrale (see
c), and supporting the second metacarpal; (3) the os magnum, a very
small bone articulating with the semilunar and centrale, and support-
ing the third metacarpal; (4) the unciform (fourth and fifth distal
carpals fused), articulating with the cuneiform, and supporting the fourth
and fifth metacarpals.

(c) The central bone (centrale) between the semilunar and scaphoid, and
appearing to belong to the distal row of carpals.

(d) The pisiform, a sesamoid bone on the posterior surface of the wrist,
articulating with the ulna and the cuneiform.

4. The hand, with five digits, each composed of a metacarpal bone and three
phalanges, except the thumb (pollex, which has only two), the last
phalanx being modified to support a claw. Note several sesamoid bones
developed in the tendons of the flexor muscles.

The pelvic girdle.

Remove each os innominatum from its muscular attachments and examine
the following parts :—

(a) The ilium, expanded anteriorly, narrowed posteriorly, articulating with
the sacrum by a roughened crescentic surface on its sacral margin, and
forming posteriorly about half the wall of the acetabulum.

(b) The ischium, forming the posterior and dorsal part of the os in-
nominatumn, having its posterior part thickened to form the ischial
tuberosity, and forming anteriorly about one-third of the wall of the
acetabulum.

(c) The pubes, the smallest bone of the three, meeting its fellow of the
opposite side in the symphysis pubis, and sending a ramus back-
wards to meet the ramus of the ischium, and enclose the obturator
foramen.

The hind limb.

Remove the muscles from the hind limb and study the following parts :—

1. The femur, an elongated bone, forming the skeleton of the thigh; its
head articulating with the acetabulum, its lower end bearing two large
condyles separated from each other by the intercondylar notch. Note,
on the ovter side of the head, the large rough great trochanter; on the
inner side of the bone just below the head, the lesser trochanter ; and
opposite to this on the outer side, the third trochanter. Examine the
knee-pan (patella), a large sesamoid bone sliding in the groove on the
lower end of the femur: and also small sesamoid bones (fabelle) at the
back of the knee-joint.
38

2. The bones of the leg, unequal in size and fused together at their distal
ends.

(a) The tibia, a stout straight bone, articulating at its upper end with the
femur by two facets, at its lower end with the astragalus.

(b) The fibula, a slender bone, articulating at its upper free end with the
outer surface of the head of the tibia, at its fixed lower end with the
caleaneum.

3. The ankle, composed of two rows of tarsal bones.

(4) The proximal row, consisting of (1) the astragalus, on the inner side,
articulating with the tibia; (2) the caleaneum (os calcis), on the outer
side of the astragalus, articulating with the fibula and having its
hinder end produced into a large calcaneal process or heel.

(b) The distal row, consisting of (1) the meso-cuneiform, a very small bone
articulating with the navicular, (see c), and supporting the second
metatarsal bone; (2) the ecto-cuneiform, on the outer side of the meso-
cuneiform, articulating with the navicular and supporting the third
metatarsal bone; (3) the cuboid, on the outer side, articulating with
the calcaneum and navicular, and supporting the fourth and fifth
metatarsal bones.

(c) The central bone (navicular) immediately in front of the astragalus,
articulating with the second metatarsal, and sending a large process
forwards along the ventral surface of the foot.

4, The foot with four digits, each composed of a long metatarsal bone, and
three phalanges, the last phalanx being modified to support a claw.
Note, on the outer side of the proximal end of the second metatarsal
bone, a backwardly directed process, probably representing the
metatarsal bone of the first (or lost) digit. :

K, General Dissection of the Brain.

Remove the muscles of the neck from their attachment to the occipital part
of the skull: remove the skin from the whole of the cranial portion: and with
bone forceps and a stout blunt scalpel remove in pieces the bones of the skull
and expose the surface of the brain, working from the foramen magnum forwards
and taking special care not to injure the brain in the region of the ear bones.
Cut through the spinal cord behind the medulla; and by help of the handle of a
scalpel, moistened with water, lift up the brain, cutting through the various
cranial nerves as far from the brain as possible.

1. Observe the dura mater covering the brain and dipping down between
the cerebral hemispheres, forming the falx cerebri; and between the
cerebrum and cerebellum, forming the tentorium. Remove the dura
mater, and note the thin vascular pia mater closely enveloping the
brain,

2. On the dorsal aspect of the brain note —

(a) The large smooth cerebral hemispheres.
40

(b) The club-shaped olfactory lobes, projecting forwards from the
cerebral hemispheres.

(c) The corpora quadrigemina, (optic lobes), only partly seen below
the cerebral hemispheres posteriorly.

(d) The pineal body, above the corpora quadrigemina, and immediately
posterior to the cerebral hemispheres.

(e) The cerebellum, large and tri-lobed. Turn back the anterior
portion of the cerebellum in order to expose the corpora quadrige-
mina and the valve of Vieussens, a thin layer of nervous tissue
stretching between the corpora quadrigemina and the cerebellum,
and forming the roof of the anterior portion of the fourth
ventricle. Note the pathetic (4th cranial) nerve arising from
the dorsal surface of the valve of Vieussens near the middle line
and looping round the brain towards the ventral surface. Note
the floccular lobes at the outer aspect of the lateral lobes,

(f) The medulla oblongata, seen on turning forwards the cerebellum.
Note—

(1) The choroid plexus (tele vasculose) of the fourth ventricle, a
portion of the pia mater covering the roof of the ventricle.
(2) The dorsal pyramids, on either side of the dorsal fissure of
the spinal cord.
(3) The restiform bodies, external to the dorsal pyramids.
(4) The fourth ventricle, its posterior portion seen on removing
the choroid plexus.
8. On the ventral aspect of the brain observe—
(a) The olfactory lobes.
(b) The cerebral hemispheres, divided by a vetiral longitudinal groove
‘into a larger superior, and a smaller inferior, lobe. A slight de-
pression on the ventral aspect of the superior lobe represents the
fissure of Sylvius.

(c) The optic tracts, optic commissure, and optic nerves. Trace the
optic tracts backwards towards the corpora quadrigemina.

(d) The infundibulum, a funnel-shaped projection to which the pituitary
body is attached.

(e) The corpus albicans (corpus mammillare), a rounded mass immedi-
ately behind the infundibulum.

(f) ‘The crura cerebri, or peduncles of the cerebrum, two broad bands
diverging from the middle line posteriorly in front of the pons
Varolii. Note the origin of the oculo-motor nerve (8rd cranial)
from the ventral surfaces of tbe crura.

(g) The pons Varolii, two strong bands of transverse fibres running from
the middle line outwards to the two halves of the cerebellum.
Note the trigeminal (5th cranial) nerve arising by two roots from
the outer posterior margin of the pons.
42

(4) The medulla oblongata, broad anteriorly, but narrower posteriorly.
Note—

(1) The ventral pyramids, on either side of the ventral fissure of
the spinal cord.

(2) The olivary bodies, one on each side, external to the ventral
pyramids.

(3) The trapezoid bodies, bands of transverse fibres, each at the
external side of the ventral pyramids anteriorly. Note the
abducent nerve (6th cranial), arising from the medulla close
to the middle line, and just behind the pons Varolii ; the
facial (7th cranial), from the outer side of the corpus trape-
zoideum anteriorly ; the auditory (8th cranial), immediately
behind this; the glosso-pharyngeal and pneumogastric
(9th and 10th cranial), from the side of the medulla by
many small roots; the spinal accessory (11th cranial),
behind this, arising by about ten small roots; and the
hypoglossal (12th cranial) from near the middle line by
several small roots.

4. The cavities of the brain, and structures connected with them. Make
a longitudinal vertical section of the brain in the middle line, and
observe—

(w) The corpus callosum connecting the two cerebral hemispheres in the
middle line.

(b) The fornix below the corpus callosum, continuous with the corpus
callosum posteriorly, but separated from it anteriorly by the cavity
of the “ fifth” ventricle.

(c) The third ventricle, bounded above and in front by the velum inter-

positum. In connection with this ventricle note—

(1) The anterior commissure, a small transverse band of fibres in
its anterior wall in front of the fornix.

(2) The middle commissure, a very thick band extending across
the middle of the ventricle, and connecting the two optic
thalami. é

(3) The posterior commissure, a small transverse band of fibres in
the posterior wall of the ventricle, immediately in front of the
corpora quadrigemina.

(4) The foramen of Monro, which brings the anterior part of the
ventricle into communication with the lateral ventricles.
Remove horizontal slices of one cerebral hemisphere to expose
the lateral ventricle, and observe the grey (cortical) matter,
the white (medullary) matter of the hemisphere, and at a
deeper level the corpus striatum.

(5) The stalk of the pineal body, an upward continuation of the
third ventricle.
44

(6) The infundibulum, the downward continuation of the third
ventricle.
(7) The corpus albicans, posterior to the infundibulum.

(d) The corpora quadrigemina, now fully exposed.

(e) The pons Varolii.

(f) The fourth ventricle, its posterior triangular portion or calamus
scriptorius, and the aqueduct of Sylvius (or iter) underneath
the corpora quadrigemina, connecting its anterior extremity with
the third ventricle.

(g) The roof of the fourth ventricle, and the cerebellum. Make a
longitudinal section of ithe cerebellum, and observe its arborescent

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