COMPARATIVE ANATOMY. 
peosate for shortness of the intestine ; and 
vice versa. The structure of the stomach 
must also be considered, as, whether it is 
formed of more than one cavity ; whetlier 
the oesophagus and intestine communicate 
with it in such a manner as to favour a 
speedy transmission of the food, or whether 
there are eul de sacs which retain the ali- 
ment for a long time in the cavity. The 
formation of the jaws and teeth, aud the 
more or less perfect trituration and com- 
minution which the food experiences in the 
mouth, must likewise be viewed in connec- 
tion with the length and structure of the 
aljraentary canal. 
The whole length of the canal is greater 
in the mammalia than in the other classes. 
It diminishes successively, as we trace it in 
birds, reptiles, and fishes, being shorter 
tlian the body in some of the latter animals, 
which is never the case in the three first 
classes. 
In omnivorous animals the length of the 
canal holds a middle rank between those 
which feed on flesh and such as take veget- 
able food; thus, in the rat, its proportion 
to tlie. body is as 8 to 1 ; in the pig 13 to 1 ; 
in man 6 or 7 to 1. The dimunition in 
length, in the latter case, is compensated 
by other circumstances, viz. the numerous 
valvul® conniventes, and the preparation 
which the food undergoes by the art of 
cookery. • 
In carnivorous animals, every circum- 
stance concurs to accelerate the passage of 
the alimentary matter. It receives no mas- 
tication ; it is retained for a very short time 
in the stomach ; the intestine has no folds 
or valves ; it is small in diameter ; and tlie 
whole canal, when compared to tlie body, 
is, extremely shortj being 3 or 5 to 1. In 
general there is no cmcuni. 
The ruminating animals present the op- 
posite structure. The food undergoes a 
double mastication, and passes through the 
vai'ious cavities of a complicated stomach. 
Ilie intestines are very long ; 27 times the 
length of the body in the ram. Hence the 
large intestines are not dilated or cellular, 
nor is there a cmcum. The solipeda have 
notsuch a length of canal, nor is their sto- 
mach complicated ; but the large intestines 
are enormous and dilated into sacculi ; and 
the caecum is of a vast size, equal, indeed, 
to the stomacli. The rodeutia, which live 
on vegetables, have a very large caecum, 
and a canal 12 or 16 times as long as the 
body. In the rat, which can take animal, 
as. well as vegetable food, the canal is shorter 
than in the other rodcntia. 
There are some exceptions to the rule 
which we have just mentioned, respecting 
the length of the canal in carnivorous and 
herbivorous animals. The seal, which take.s 
animal food, has very long intestines : the 
sea-otter resembles it in this respect, and 
differs therein most remarkably from the 
common otter, which resembles other car- 
nivorous animals in tlie shortness of its in- 
testinal tube. The length of canal in the 
former is twelve times that of the animal, 
and only three times and a quarter in the 
latter. (Home, in the Philos. Trans. 1799, 
part 2.) Whales have likewise a longer 
canal than other carnivorous mammalia; 
tlieir stomach is complicated, and the in- 
testine has longitudinal folds. It seems, 
therefore, that a considerable length of in- 
testinal canal is found in all mammalia, 
which live much in the water, although 
they are carnivorous. 
The plantigrade animals, which have car- 
nivorous teeth, but feed equally w'ell on 
vegetables, have a long canal ; but it is very 
narrow and possesses no caecum, nor dis- 
tinction of large intestine. 
A species of bat (vespertilio noctula) 
seems to have the shortest intestinal canal 
of any mammalia ; it is only twice the length 
of the animal’s body. On the contrary, the 
roussette (vesp. vampyrus Linn. v. caninus 
Blum.) which lives entirely on vegetables, 
has it seven times as long. 
In a few instances, as the beaver and 
sloth, the rectum and uretha have a com- 
mon termination, w’hich may be compared 
to the cloaca of birds. This resemblance is 
the most striking in the ornithorhynchus. 
A remarkable difference is observed in 
the length of the canal between the w'ild 
and domesticated breeds of the same 
species. In the wdld boar the intestines 
are to the body as nine to one ; in the tame 
animal these proportions are as thirteen to 
one; in tire domestic cat, five to one; in the 
wild cat, three to one ; in the bull, twenty- 
two to one ; in the buffalo, twelve to one. 
They are, on the contrai-y, longer in the 
wild than in the tame rabbit ; the propor- 
tions in tire former being eleven, and in the 
latter nine to one. 
The proportion of the intestinal canal to 
the length of the body in birds, is as two, 
three, four, or five, to one. It is not always 
longest and largest in the graminivorous 
species, as many piscivorous birds have it 
equally long. 
It is hardly twice the length of the body 
in many reptiles ; and not so much in the 
