418 Till- IHGESTIVK APPARATUS IN MAMMALIA. 



The tmall intestine proper is suspended by a mesentery somewhat simihir to tlmt of 

 tin Horse. Its length varies much from 13 to 2G feet. It* internal fu-v has n lime 

 number of transverse rugaj, tin; ralnili <;,,,ni rentes. It also shows from 20 t" 'J-"> 

 I'. \ r's patches, particularly in the ileo-ciecal portion. Its structure is like that already 

 describe*!. 



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



The caecum is a small reservoir placed in the right iliac fossa, a little <.l.li<iu.-!y 

 downwards and to the left. It commences at the ileo-cjccal valvi-, has an average lengto 

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

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

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



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 tin- 

 liver, passes abruptly across from right to left, and, arriving at the spleen, a^ain changes 

 its direction downwards to the iliac fossa : it then again describes the iliac 8, to r< ach 

 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 detctn<1in>j 

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

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



There is scarcely anything special to note in the rectum and anus, except that tin -y, 

 and esj)ecially the latter, are very rich in arteries and varicose veins?, and that the anus 

 is separated from tlie rectum by small cavities open in front, and which are found in 

 the Dog ; these are the sinuses of Morgagni. 



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 

 tin c ssential portion of the alimentary canal in all the domesticated animals, and whnt 

 gradations has 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), we 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 Omnivoru, 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 

 unfitted 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 veget-iblc 

 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 sin tact- 

 being relatively more extensive in Ruminants than in Soli pi <!.-. 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 highe.-t 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 remarkal le differences. The 

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

 exposed to frequent fastings; it is, therefore, necessary tnnt they should L 

 stomach large enough to contain the invested substances, and to seen te the amount of 

 g i. -trie juice needed to transform them int-i a-.-imilahle materials. IHln-M- animals have 

 :i -hurt 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, ami readily conn- in contact with the absorbing membrane. 



With regard to the Herbivnra. tin ir food contains a trilling pro])ortion of nutritive 

 elements inclosed in an extremely abundant nntrix. and U-ing compelled to ingeM 



