418 THE DIGESTIVE APPARATUS IN MAMMALIA. 



The small intestine proper is suspended by a mesentery somewhat similar to that of 

 the Horse. Its length varies much from 13 to 26 feet. Its internal face has a large 

 number of transverse rugse, the valvulse conniventes. It also shows from 20 to 25 

 Pt-yer's patches, particularly in the ileo-csecal portion. Its structure is like that already 

 described. 



In the large intestine is recognised the caecum, colon, and rectum. 



The ceecum is a small reservoir placed in the right iliac fossa, a little obliquely 

 downwards and to the left. It commences at the ileo-csecal valve, has an average length 

 of about 2 inches, and terminates by a rounded extremity with a small hollow prolong- 

 ation, averaging 3 inches in length, the cxcal or vermiform appendix. The mucous 

 membrane is like that of animals, and the muscular tunic is the same. 



The human colon is regularly sacculated, like the small colon of the Horse ; it begins 

 in the right iliac fossa, above the valvula Bauhini; it ascends to the lower face of the 

 liver, passes abruptly across from right to left, and, arriving at the spleen, again changes 

 its direction downwards to the iliac fossa ; it then again describes the iliac S, to reach 

 the mesial line, where it is continued by the rectum. From this course, the colon has 

 been divided into three portions : the ascending colon, transverse colon, and descending 

 colon. In the ascending and transverse colon are observed three series of sacculi, 

 separated by three muscular longitudinal bands; the descending colon has only two. 



There is scarcely anything special to note in the rectum and anus, except that they, 

 and especially the latter, are very rich in arteries and varicose veins, and that the anus 

 is separated from the rectum by small cavities open in front, and whicli are found in 

 the Dog ; these are the sinuses of Moryagni. 



GENERAL AND COMPARATIVE SURVEY OP THE ABDOMINAL OR ESSENTIAL PORTION OF THE 



DIGESTIVE TUBE. 



We have terminated the description of the anatomical characters which distinguish 

 the essential portion of the alimentary canal in all the domesticated animals, and what 

 gradations lias this study revealed ! Let .us recapitulate and compare them, before 

 showing the admirable harmony which pervades these diverse arrangements, and 

 adapts them to the variations in general organisation, habits, and instincts. 



In the Carnivora which subsist on flesh (Dog and Cat), \ve have seen a very ample 

 stomach, secreting a gastric fluid throughout the whole extent of its mucous membrane, 

 and intestines, (relatively; extremely short. 



In the Omnivora, or mammalia which live on a mixed diet (Pig], we have found a 

 small portion of the internal surface of the stomach occupied by a mucous membrane 

 unfitte-1 to secrete gastric juice, and the intestines relatively of much more considerable 

 capacity than in Carnivora. 



With the Herbivora, which derive their nourishment exclusively from the vegetable 

 kingdom (Ruminants and Solipeds), the surface destined for the production of the gastric 

 juice also singularly diminishes in extent, although the stomach in some of these animals 

 is remarkable for its extraordinary development. But to compensate for this, the 

 capacity of the intestinal canal assumes considerable proportions, and in the various 

 species is in directly inverse relation to the area of the gastric surface. This surface 

 being relatively more extensive in Ruminants than in Solipeds, all these animals ought 

 to be classed in an inverse order with regard to the development of the intestinal 

 surface. 



Finally, in considering as the internal surface of the stomach fa point of view quite 

 rational) only those portions of the mucous membrane organised for the secretion of the 

 gastric juice, we are led to recognise that this surface is in inverse proportion to that of 

 the intestine; that it reaches its highest degree of development in Carnivorous animals; 

 and that it is reduced to the smallest dimensions in Solipeds, animals which, on the 

 contrary, present a very great development of the intestinal surface. 



The nature of the aliment readily accounts for these remarkable differences. The 

 Camivora, living on substantial food, take it in very large quantity, because they are 

 exposed to frequent fastings; it is, therefore, necessary that they should have a 

 stomach Ltrge enough to contain the ingested substances, and to secrete the amount of 

 g istric juice needed to transform them into assimilable materials. If these animals have 

 a short and narrow intestine, it is because a small surface only is required to absorb the 

 products of digestion, these being mixed with but a minimum quantity of non-nutritive 

 substances, and readily come in contact with the absorbing membrane. 



With regard to the Herbivora, their food contains a trifling proportion of nutritive 

 elements inclosed in an extremely abundant matrix, and being compelled to ingest great 



