COMPARATIVE anatomy. 
Oestined to that purpose. They have in 
general many more bones unconnected with 
tlie rest of the skeleton, than the animals 
of the preceding classes. 
The cranium in several cartilaginous 
fishes, (in the skate for instance) has a very 
simple stracture, consisting chiefly of one 
large piece. In the bony fishes, on the 
contrary, its component parts are very nu- 
merous ; amounting to 80 in the head of the 
perch. Most of the latter have a more or 
less moveable under-jaw. 
Great variety in the structure of the 
teeth is observed in this class. Some ge- 
nera, as the sturgeon, are toothless. Their 
jaws, which are distinct from the cranium, 
form a moveable part, capable of being 
thnist forwards from the mouth, and again 
retracted. 
Those fishes which possess teeth, differ 
very much in the form, number, and posi- 
tion of these organs. Some species of spa- 
ms, (as the S. probato-cephalus) have front 
teeth almost like those of man ; they are 
provided with fangs, which are contained 
in alveoli. In many genera of fishes, the 
teeth are formed by processes of the jaw- 
bones covered with a crust of enamel. In 
most of the sharks, the mouth is furnished 
with very numerous teeth for the supply of 
such as may be lost. The white shark has 
more than two hundred, lying on each 
other in rows, almost like the leaves of an 
artichoke. Those only which form the 
front row have a perpendicular direction, 
and are completely uncovered. Those of 
the subsequent rows are, on the contrary, 
smaller j have their points turned back- 
wards, and are covered with a kind of gum. 
These come through the covering sub- 
stance, and pass forward when any teeth of 
tlie front row are lost. It will be under- 
stood from this description, that the teeth 
in question cannot have any fangs. 
The saw-fish only (squalus pristis) has 
teeth implanted in the bone on both sides 
of the sword-shaped organ, with which its 
head is armed. 
In some fishes the palate, in others the 
bone of the tongue (as in the frog-fish), in 
others (as in several of the ray-kind), the 
aperture of the mouth forms a continuous 
surface of tooth. 
MOUTH, OESOPHAGUS, AND STOMACH. 
We have already shown the most impor- 
tant circumstances relating to the mouth. 
Many species of the genus simia, as well 
as the hamster, (marmota cricetus) and 
some similar species of the marmot; are pro" 
vided with cheek pouches, in which tlie 
former, who live on trees, place small quan- 
tities of food as a reserve : the latter em- 
ploy these bags to convey their winter pro- 
vision to their burrows. 
The peculiar glandular and moveable 
bag, (bursa faucium) which is placed be- 
hind the palate, has hitherto been only ob- 
served in the camels of the old world : and 
it probably serves to lubricate tlie throat of 
these animals in their abode in the dry 
sandy deserts which they inhabit 
The oesophagus of quadrupeds is distin- 
guished from that of the human subject by 
possessing two rows of muscular fibres, 
which pursue a spiral course, and decussate 
each other. In those carnivorous animals 
which swallow voraciously, as the wolf, it 
is very large ; on the contrary, in many of 
tlie larger herbivora, and particularly in 
such as ruminate, its coats are proportion- 
ally stronger. 
No mamnialia possess an uvula, except 
man and the simia. 
In some herbivora the stomach has an 
uniform appearance externally ; but it is di- 
vided into two portions internally, either 
by a remarkable difference in the two 
halves of its internal coat, as in the horse, 
or by a valvular elongation of this mem- 
brane, as in several animals of the mouse- 
kind. This is also the case in the hare and 
rabbit, where also tlie food in the two 
halves of the stomach differs very much in 
appearance, particularly if the animal has 
been fed about two hours before death. 
In these animals the left half of the sto- 
mach is covered with cuticle, while the 
other portion has the usual villous and se- 
creting surfaee. The left portion of the ca- . 
vity may be regarded as a reservoir, from 
which the food is transmitted to the true di- 
gestive organ ; and the different states in 
which the food is found in the two parts of 
the cavity justify this supposition. Hence 
these stomachs form a connecting link be- 
tween those of ruminating animals on one 
side, and those which have the whole sur- 
face villous on tlie , other. 
On the whole internal surface of the 
horse’s stomach there are found in vast 
abundance, particularly in spring, the lar- 
vas of two species of cestrus ; viz. the oestrus 
equi (which Linnaeus called oestrus bovis, and 
the oe. hJemorrhoidalis, the true history of 
which has been elucidated, for the first 
time in modem days, by that excellent ve- 
terinary surgeon Mr. Bracy Clark, in the 
