DIGESTIVE ORGANS. 231 
there is a relation between the development of cecum and stomach. The cecum 
becomes enormous in certain rodents and marsupials (sometimes longer than the 
body) and plays an important part in digestion, being sometimes lobulated or 
furnished with internal folds, those of the rabbits being arranged in a spiral manner. 
In man and the anthropoids and some other forms, as is well known, the distal part 
of the caecum degenerates to a rudiment, the vermiform appendix, which tends to 
become obliterated with increasing age. 
, 
‘ag 
Fic. 236. FIG. 237. 
Fic. 236.—Diagrammatic longitudinal section of the cloacal region of a duck embryo 
at the twenty-second day. of incubation, after Poindyer. ag, anal groove; c, cloaca; cp, 
cloacal plate; f, bursa Fabricii; p, phallus, with cecal duct; sp, stercoral pouch of rectum. 
Fic. 237.—Semidiagrammatic course of intestine of new-born deer Cervus canadensis, 
after Weber. c, cecum; d, duodenum; co, colon; 7, jejunum; m, mesentery. 
Both small intestine and colon are at first straight, but with growth they become 
longer, involving convolutions varying in pattern and extent in different groups, 
the patterns of the colon being of some systematic value. The full history has 
been worked out only for man, two stages being represented in figure 238. The 
genus Hyrax is remarkable for a pair of cecal diverticula arising from the colon 
(fig. 239). In the monotremes the rectum terminates in a cloaca as in the saurop- 
sida, and the same condition occurs in the young of all higher mammalia. In the; 
later stages, however, the urogenital and digestive openings become separated by 
the formation of a perineal fold between the two. 
THE LIVER (HEPAR). 
The liver, the largest gland in the body, has several functions. It 
secretes the bile (gall) and forms several internal products such as 
glycogen, urea and uric acid, of great importance in the animal economy. 
