256 DIGESTIVE SYSTEM. 



THE JEJUNUM, paler, less in caliber, and much longer 

 than the duodenum, is extremely tortuous in its course, floating 

 about loosely within the cavity together with the convolutions of 

 the ileum : there is, in fact, little or no distinction between these 

 guts, except that the latter, by an arbitrary division, is longer 

 by one-fifth than the former. 



THE ILEUM is the longest of the small (and indeed of all 

 the) intestines : it forms the greater part of that convoluted tube 

 which lies principally in the umbilical region. Probably it is 

 still less vascular (being somewhat paler) than the jejunum. It 

 is certainly less in caliber towards its posterior extremity ; which 

 ends, rather abruptly, in the beginning of the large intestines. 

 The jejunum and ileum being attached to the spine by that 

 loose doubling of peritoneum, the mesentery, can move about 

 within the cavity, regulating their movements and relative posi- 

 tion according to the volume of the stomach and stage of the 

 digestive process. 



Organization. — The small intestines are supplied with blood 

 by the aiderior mesenteric artery ', a vessel of large size, that, 

 after having divided and subdivided many times, sends off nu- 

 merous small branches, which ramify to great minuteness between 

 their muscular and villous coats. Their veins, which have no 

 valves, return the blood into the vena portae. The nerves come 

 from the mesenteric plexus. 



Capacity. — The small intestines altogether will contain about 

 eleven gallons of fluid. 



Large Intestines. 



The large intestines are shorter in length, but considerably 

 more bulky in volume, than the small. They also differ re- 

 markably from the latter in their general appearance — in being 

 puckered into numerous plaits or folds. This peculiarity is oc- 

 casioned by some longitudinal muscular bands, which, not being 

 so long as the rest of the intestine, pucker its coats, and contract 

 them into folds : to these bands are appended numberless little, 

 fatty processes, to which anatomrsts have given the name of 

 appendiculcE pingnedinosce. Interiorly, the large intestine is di- 

 vided into many little elliptical pouches, denominated ce//s, with 

 partitions between them ; which, though they appear to answer 

 similar purposes as the valvulae conniventes of the human intes- 

 tine, viz. the retardation of the passage of the contents and the 

 augmentation of the surface for absorption, differ essentially 

 from them in being constituted of all the coats of the gut. In 

 other respects, the structure of the large and small guts is not 

 materially diff'erent. 



