CHAP. XIV.] ALIMENTATION. 159 



leading into the small intestine, the pyloric. The pyloric aper- 

 ture is guarded by a kind of valve composed of circular mus- 

 cular fibres, which form a constricted ring projecting into the 

 pyloric opening. By this arrangement, the food is kept in 

 the stomach until it is ready for intestinal digestion, when the 

 circular fibres relax and allow it to pass. 



When moderately distended, the stomach measures about 

 four inches vertically and twelve inches from side to side. It 

 has four coats. The^ outer serous coat is formed by a fold of 

 the peritoneum. The fold is slung over the stomach, in 

 much the same way as 

 we sling a towel over a 

 clothes-line, and covers it 

 before and behind. The 

 anterior and posterior 

 folds unite at the lower 

 border of the stomach 

 and form an apron-like 

 appendage, the omentum, 

 which covers the whole 

 of the intestines. The 

 omentum often contains 

 a large amount of fat. FlG 97 ._ VERTICAL AND LoNGITUDINAL SEC- 



The muscular COat of TION OF STOMACH AND DUODENUM. 1, cesopha- 

 i-t i ' i r gus, on its internal surface the folds or ruga? of 



the stomach consists of f he mucous membrane are shown; 2> c{ T rd5ac 



three layers of UHStriped orifice of stomach ; 5, lesser curvature ; <>, greater 

 -, ,. curvature; 8, rugae in interior of stomach; 9, 



muscular tissue: an outer, pyloric orifice; 10> n> 13> inte rior of duodenum 



formed of longitudinal showing valvulre conniventes ; 12, duct conveying 

 , ., ,, ,. the bile and pancreatic juice into duodenum; 15, 



fibres ; a middle, OI Cir- commencement of jejunum. 



cular; and an inner, of 



less well-developed, obliquely disposed fibres. The alternate 

 contraction and relaxation of these fibres causes the food to 

 be carried round and round the stomach, and at the same time, 

 subjects it to considerable pressure. 



The mucous membrane is very soft and thick, the thickness 

 being mainly due to the fact that it is densely packed with small 

 tubular glands; it is covered with columnar epithelium, and in 

 its un distended condition is thrown into folds or rugae. The 

 surface is honeycombed with tiny shallow pits, into which the 

 ducts or mouths of the tubular glands open. The glands are 



