COMPARATIVE ANATOMY. 



very long, and the sloth very short, intes- 

 tines ; the badger, which is not a proper 

 carnivorous animal, and several true her- 

 bivora, as for instance, the rell-mouse, 

 (glis esculentus,) have no distinction be- 

 tween the large and small intestine, &c. 



In considering the proportionate 

 lengths of the intestinal canal, and the 

 relation which these bear to the kind of 

 food on which the animal subsists, many 

 circumstances must be taken into the ac- 

 count, besides the mere measure of the 

 intestine. Valvular projections of the in- 

 ternal membrane ; dilatations of peculiar 

 parts of the canal ; and a large general 

 diameter, compensate 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 ; whether the oesophagus and in- 

 testine communicate with it in such a 

 manner as to favour a speedy transmission 

 of the food, or whether there are cul de 

 sacs which retain the aliment for a long 

 time in the cavity. The formation of the 

 jaws and teeth, and the more or less per- 

 fect tritu ration and comminution which 

 the food experiences in the mouth, must 

 likewise be viewed in connection with 

 the length and structure of the alimenta- 

 ry canal. 



The whole length of the canal is great- 

 er in the mammalia than in the other 

 classes. It diminishes successively, as we 

 trace it in birds, reptiles, and fishes, be- 

 ing shorter than 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 the flesh and such as 

 take vegetable food ; thus, in the rat, its 

 proportion to the body is as 8 to 1 ; in 

 the pig 13 to 1 ; in a man 6 or 7 to 1. The 

 diminution in length in the latter case 

 is compensated by other circumstances, 

 viz. the numerous valvulac conniventes, 

 and the preparation which the food un- 

 dergoes by the art of cookery. 



In carnivorous animals, every circum- 

 stance concurs to accelerate the passage 

 of the alimentary matter. It receives no 

 mastication ; it is retained for a very 

 short time in the stomach ; the intestine 

 has no folds or valves ; it is small in di- 

 ameter : and the whole canal, when com- 

 pared to the body, is extremely short, 

 being 3 or 5 to 1. In general there is 

 no caecum. 



The ruminating animals present the 

 opposite structure. The food undergoes 

 a double mastication, and passes through 



the various cavities of a complicated sto- 

 mach. The 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 caecum. 

 The solipeda have not such a length of 

 canal, nor is their stomach complicated ; 

 but the large intestines are enormous, and 

 dilated into sacculi ; and the caecum is of 

 a vast size, equal, indeed, to the stomach. 

 The rodentia, which live on vegetables, 

 have a very large caecum, and a c'anal 12 

 or 16 times as long as the body. In the 

 rat, which can take animal as well as ve- 

 getable food, the canal is shorter than in, 

 the other rodentia. 



There are some exceptions to the 

 rule which we have just mentioned, res- 

 pecting the length of the canal in carni- 

 vorous and herbivorous animals. The 

 seal, which takes 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 carnivorous ani- 

 mals in the shortness of its intestinal 

 tube. The length of canal in the former 

 is twelve times that of the animal, and 

 only three times and a quarter in the lat- 

 ter. (Home, in the Philos. Trans. 1799, 

 part 2.) Whales have likewise a longer 

 canal than other carnivorous mammalia ; 

 their stomach is complicated, and the in- 

 testine has longitudinal f >lds. It seems, 

 therefore, that a considerable length of 

 intestinal canal is found in all mammalia 

 which live much in the water, although 

 they are carnivorous. 



The plantigrade animals, which have 

 carnivorous teeth, but feed equally well 

 on vegetables, have a long canal ; but it 

 is very narrow, and possesses no caecum, 

 nor distinction of large intestine. 



A species of bat (vespertilio noctula) 

 seems to have the shortest intestinal ca- 

 nal of any mammalia ; it is only twice the 

 length of the animal's body. On the 

 contrary, the rousette (vesp. vampyrus, 

 Linn. v. caninus, Blum.) which lives en- 

 tirely on vegetables, has it seven times as 

 long. 



In a few instances, as the beaver and 

 sloth, the rectum and urethra have a com- 

 mon termination, which may be compar- 

 ed to the cloaca of birds. This resem- 

 blance is the most striking in the orni- 

 thorhynchus. 



A remarkable difference is observed 

 in the length of the canal between the 

 wild and domesticated breeds of the 

 same species. In the wild boar the intes- 

 tines are to the body as nine to one ; in 



