THE SMALL INTESTINE. 283 



The general appearance may be demonstrated by making a 

 longitudinal section of the pylorus and small intestine as shown in 

 Fig. 79. 



736. Obvious Structure of the Stomach. With a scalpel, make a longitudinal incision 

 in the stomach along its entire ventral surface, and wash out the contents. With scis- 

 sors, cut out a piece of the stomach 2-3 cm. square. Look at the cut edge with a tripod 

 magnifier after observing it well with the naked eye. It will be seen to be composed of 

 two very obvious coats, an ectal, firm muscular coat, covered by the thin peritoneum, and 

 an ental, soft mucous coat. These are somewhat loosely connected together, and if the 

 stomach is empty or but slightly filled, the mucous coat will be thrown into folds or rugae, 

 mostly longitudinal in direction, by the contraction of the muscular coat. 



Micros&tpic Structure, commencing ectad : (A) Peritoneal or serous coat. (B) Muscu- 

 lar (unstriped) coat of: (1) Ectal longitudinal layer; (2) intermediate circular layer; 

 (3) ental oblique layer. (C) Submucosa, loose connective tissue coat. (D) Muscularis 

 mucosa, a thin layer of unstriped muscular fibers both circularly and longitudinally 

 arranged. (E) Mucous coat, with peptic glands. See Strieker, A, 370 ; Quain, A, II, 350. 



737. Splen, az. Spleen ( 715). The relations, form and tex- 

 ture of the spleen should be carefully noted. It is one of the so 

 called ductless glands, and its functions are not well understood. 



738. Intestinum tenue, az. Small intestine (Fig. 77, 717). 

 The small intestine is arbitrarily divided into three regions : The 

 duodenum, the jejunum and the ileum. 



(A) Duodenum. That part of the small intestine along which the 

 pancreas extends is called the duodenum. It is held rather firmly 

 in position by a ligament from its caudal end. Into the duodenum 

 empty the ductus choledochus communis (Fig. 81 and 82) and the 

 two pancreatic ducts. 



(B) Jejunum. This is an ill-defined portion of the small intes- 

 tine immediately following the duodenum. It is so called because 

 in man it is often found empty after death. 



(C) Ileum. This is the caudal part of the small intestine, and is 

 a continuation of the jejunum, as that is of the duodenum. It ter- 

 minates in the large intestine, entering it obliquely. At its termina- 

 tion is the ileo-ccecal valve, which allows the alimentary contents to 

 pass from the small to the large intestine, but not easily in the 

 opposite direction. The action of this valve may be demonstrated 

 by cutting a slit in the small intestine 5-10 cm. cephalad of its ter- 

 mination, and injecting water caudad. The water will pass readily 

 into the large intestine. 



Now cut a small slit in the large intestine and inject water toward 

 the small intestine. It will pass with difficulty into the small in- 

 testine. 



