COMPARATIVE ANATOMY. 
and in front of them in the calmar; but in 
the common cnttle-fish (“ sepia officinalis”), 
it is at a considerable distance from tliis 
organ. 
The real bile is poured, as usual, into tlie 
alimentary canal. 
The structure of the pancreas in the 
mammalia, in birds, and in reptiles is the 
same, on the whole, as in the human sub- 
ject, its form and size, its colour and con- 
sistence, and its division into lobules exhibit 
some slight and unimportant variations. 
The termination of its duct or ducts is 
distinct in birds from that of the D. cho- 
ledochus. In the mammalia they generally 
open together, or there is a branch termi- 
nating in the D. choledochus, and another 
opening into the intestine, as in the dog 
and elephant, or they may be quite dis- 
tinct, as in the hare, porcupine, and mar- 
mot. They may be separate or distinct in 
different individuals of the same species, 
as in the monkeys. 
The skate and shark liave a pancreas 
similar to tliat of the three first classes of 
red-blooded animals. In other fishes tlie 
situation of this organ is occupied by nu- 
merous small tubes, called the coecal ap- 
pendices, or pyloric caeca ; which afford a 
copious secretion, analogous, no doubt, to 
the pancreatic liquor. The internal sur- 
face of these tubes becomes very red on 
injection, and possesses a glandular and 
secreting appearance. Their number va- 
ries from one to several hundreds. 
Tire description of the organs, which are 
concerned in assimilating the food, and in 
converting it into chyle, will be naturally 
followed by that of the blood-vessels which 
carry itto all parts of the body, of the or- 
gans of respiration, which subject it to 
contain important changes, and of the ab- 
sorbent system. 
ORGANS OF CIRCULATION. 
A perfect circulating system, to which 
on the one hand fluids are brought by the 
absorbents to be converted into blood ; 
and from which on the other side, various 
juices are separated in glands, and viscera 
of a glandular structure, appears to belong 
universally and exclusively to red-blooded 
animals. A pericardium exists in all these 
animals. Parts of such a system, particu- 
larly a heart, and certain vessels connected 
with it, are found in some genera of the 
white blooded classes. 
It has been supposed, that the amphi- 
bious animals of this class, and the cetacea 
have an open foramen ovale, like that of 
the fcetus, in their septum auricnlarum. 
And the necessity of such an opening has 
been inferred from their way of life ; since 
they often pass' a considerable time under 
water without breathing. This supposition 
has been fully refuted by the repeated dis- 
section of adult animals of this kind ; which 
has shewn that an exception from the gene- 
ral rule very rarely occurs. 
In several genera and species of web- 
footed mammalia, and cetacea (that is, in 
the common and sea-otters, in the dolphin, 
&c.) particular vessels have been ob- 
served to be considerably and constantly 
enlarged and tortuous. This structure has 
been principally remarked in the inferior 
vena cava ; where there can be no doubt 
that it serves, while the animal is under 
water, to receive a part of the returning 
blood, and to retain it until respiration 
can be again performed, and the lesser cir- 
culation be thereby again put in action. 
There are some remarkable circum- 
stances in the distribution of particular ar- 
teries in certain animals of this class. We 
may notice, as the most singular of these, 
the rete mirabile, formed by the internal 
carotid at its entrance into the ci'anium, 
in several ruminating biscula, and carnivo- 
rous animals ; and that division of the ar- 
terial trunks of the extremities, which has 
been observed by Mr. Carlisle in the slow- 
moving animals, viz. the sloths, and lemur 
tardigradus. The arteries of the arm and 
thigh in these cases, divide as they leave the 
trunk into numerous parallel branches, 
which are united again towards the elbow 
and knee. 
All birds possess a very remarkable pe- 
culiarity in the structure of the heart, The 
right ventricle, instead of having a mem- 
braneous valve (such as are found in both 
ventricles of mammalia, and also in the left 
of birds), is provided with a strong, tense, 
and nearly triangular muscle. This singu- 
lar structure assists in driving the blood 
with greater force from the right side of 
the heart into the lungs : since the expan- 
sion of the latter organs by respiration, 
which facilitates the transmission of the car- 
bonated blood ill mammalia, does not take 
place in birds, on account of the connection 
which their lungs have with the numerous 
air-cells, which will be afterwards de- 
scribed. 
Frogs, lizards, and serpents, have a sim- 
ple heart, consisting of a single ventricle 
and auricle. 
