CHAP. XV.] ALIMENTATION. 185 



straight across the abdomen as the transverse colon until, reach- 

 ing the left side, it turns abruptly and passes downwards as the 

 descending colon. Reaching the left iliac region on a level with 

 the. margin of the crest of the ileum, it makes a curve like the 

 letter S, hence its name of sigmoid flexure, and finally ends 

 in the rectum. The rectum is from six to eight inches (152 to 

 203 mm.) long ; it passes obliquely from the left until it reaches 

 the middle of the sacrum, then it follows the curve of the sacrum 

 and the coccyx, and finally arches slightly backwards to its 

 termination at the anus. The anal opening is guarded by two 

 circular muscles called, respectively, the internal and external 

 sphincters. 



The large intestine has the usual four coats, except near its 

 termination, where the serous is wanting. The muscular coat, 

 along the caecum and colon, has a peculiar arrangement. The 

 longitudinal fibres are gathered up in three thick bands, and 

 these bands, being shorter than the rest of the tube, the walls are 

 puckered between them. The mucous coat possesses no villi 

 or valvulse conniventes, but is usually thrown into effaceable 

 folds, somewhat like those of the stomach. It contains nu- 

 merous glands, resembling the crypts of Lieberkiihn found in 

 the small intestine. 



Accessory organs of digestion. The accessory organs of diges- 

 tion are the teeth and salivary glands (which have already been 

 sufficiently described), the pancreas, and the liver. 



The pancreas. The pancreas is a compound, secreting gland, 

 closely resembling the salivary glands in structure, except that 

 the secreting cavities are saccular in the salivary glands, and 

 more distinctly tubular in the pancreas. The cavities are 

 grouped in small lobes or lobules, each lobule having its own 

 duct. The lobules are joined together by connective tissue to 

 form lobes, and the lobes, united in the same manner, form the 

 gland. The small ducts open into one main duct, which, run- 

 ning lengthwise through the gland, pierces the coats of the duo- 

 denum and pours its contents into the interior of the intestine. 

 The secretion formed in the pancreas is called the pancreatic juice. 



In shape, the pancreas somewhat resembles a dog's tongue. 

 It is a flat, elongated organ, about six to eight inches (152 to 

 203 mm.) in length, one and a half inches (38 mm.) in width, 

 and from half an inch to an inch (12.7 to 25.4 mm.) thick. 



