CHARACTERISTICS OF THE DIGESTIVE APPARATUS. 221 



the alimentary canal of the herbivora. The extent of surface for absorp- 

 tion in the intestinal tube is still further increased by the formation of 

 plicie, or folds of mucous membrane, and from what has been said above 

 we would naturally expect that these are more extensive and more highly 

 developed in the herbivora than in the carnivora. This is well exem- 

 plified in the case of the ox, whose stomach, which is capable of contain- 

 ing two hundred litres, has onh r two square meters of external surface, 

 and yet whose internal mucous surface amounts to nine square meters. 

 Such an immense increase of internal over external surface could only 

 be accomplished by the throwing up of the mucous 'membrane into folds. 

 In the intestine, again, which is capable of holding about sevent3 7 -five 

 litres, the square surface externally amounts to fifteen or sixteen meters, 

 showing, therefore, that in the ox the mucous coating of the intestine 

 is more simple. 



The carnivora are distinguished by a large, voluminous stomach, 

 coated throughout with a secreting mucous membrane, and the intestine 



FIG. 78. C^CUM OF A DOG, INFLATED. (Strangeways.) 



A, ileum ; B, caecum ; C, colon. 



is simple and deprived of folds. With the exception of the cetacea and 

 a few edentata, the subdivision into a small and large intestine prevails 

 throughout the entire group of mammals. The greater the length of 

 the small intestine, the more is it convoluted. Yilli are always absent 

 from the large intestine. A well-marked ileo-caecal valve, with but few 

 exceptions, is situated at the junction of the small and large intestines. 



At this point, also, is almost invariably found a diverticulum, 

 called the caecum, which varies very greatly in size and functional impor- 

 tance in different animals, these differences also being dependent upon 

 differences in regimen. In the carnivora the caecum is only a spiral 

 appendix, as seen in the dog (Fig. 78), and the large intestine is divided 

 into the ascending, transverse, and descending portions, as in man ; there 



