DIGESTIVE ORGANS. 227 



divided into chambers, the division reaching its extreme in the rumi- 

 nants (fig. 229) and the cetacea (fig. 228, E) where four compart- 

 ments can be recognized. In the ruminants two of these, the rumen 

 or paunch and the reticulum or honey-comb are expansions of the 

 oesophagus and serve as reservoirs for food before its complete mastica- 

 tion, after which it follows the course of the dotted lines to the 

 psalterium, omasus or manyplies and the abomasus or rennet 

 stomach for gastric digestion. 



INTESTINE. 



The remainder of the pre-hepatic portion of the alimentary canal, 

 the duodenum, extending from the pylorus to the entrance of the bile 

 duct, is considered as part of the intestine. It is especially noticeable 



FIG. 230. Digestive tube of garpike, Lepidosteus (after Gegenbaur). i, small intestine; 

 oe, oesophagus; pc, pyloric caeca; pg, pylorus; r, rectum; s, stomach; sv, spiral valve. 



in many ganoids and teleosts (figs. 230, 233) where it may bear from 

 one to two hundred blind digestive tubes, the pyloric caeca. The 

 same region in a few elasmobranchs may have a pair of these caeca or 

 (Galeus) it may be expanded into a pouch ('bursa Entiana'). 



The post-hepatic intestine is the seat of most of the digestive pro- 

 cesses and of absorption of the products of digestion. Here the food, 

 coming from the stomach, is mixed with the bile frorn the liver and 

 with the pancreatic juice and with the secretions of numerous small 

 glands in the intestinal wall. The increase of surface needed for ade- 

 quate digestion and absorption is provided in several ways. There 

 may be an elongation of the tube which results in its becoming coiled in 

 the body cavity; the mucous lining may develop folds, both longitudinal 

 and circular; or the folds may break up into numerous minute, finger- 

 like processes (villi) which give the surface a velvety appearance. The 

 food undergoing digestion is moved back and forth (peristaltic mo- 

 tion) by the antagonistic action of the muscles of the intestinal wall 

 (p. 207), bringing all of it in contact with the absorb tive surface. 



