THE STOMACH 



359 



the great colon; the spleen, small colon, and small intestines are pushed back by the distention of 

 the left sac. 



Structure. — The wall is composed of four coats — serous, muscular, submucous, 

 and mucous. 



The serous coat (Tunica serosa) covers the greater part of the organ and is 

 closely adherent to the muscular coat except at the curvatures. It partially bridges 

 over the lesser curvature, and covers here elastic tissue which assists in retaining 

 the bent form of the stomach. The peritoneal folds have been described. 



The muscular coat consists of three incomplete layers, an external of longitu- 

 dinal, a middle of circular, and an internal of oblique fibers. The layer of longi- 

 tudinal fibers (Stratum longitudinale) is very thin and exists only along the curva- 

 tures and at the antrum. At the lesser curvature it is continuous with the longi- 



Scicriis arois 

 {left extrettiity) 



CE.'iophagfdl region 

 {iion-glundular) 



Cuticu 

 lar line 



Fundus 

 gland 

 region 



Duodenal 

 diverticulum 



Pyloric gland region 



Fig. 261. — Frontal Sectiox of Stomach and First Part of Duodenum of Horse. 

 C, Cardiac orifice. Photograph of specimen fixed in situ. 



tudinal fibers of the oesophagus. On the antrum pylori it forms a well developed 

 complete layer. The layer of circular fibers (Stratum circulare) exists only on 

 the right sac. At the pyloric orifice it forms a thick ring— the pyloric sphincter. 

 Another ring, the antral sphincter, is found at the left end of the antrum pylori. 

 The oblique fibers (Fibrae obliquse) are arranged in two layers; the external stratum 

 covers the left sac and is a continuation (in part) of the longitudinal fibers of the 

 oesophagus; the internal stratum is found also on the left sac, and exchanges fibers 

 with the circular and external oblique layers. It forms a remarkable loop around 

 the cardiac orifice, constituting a powerful cardiac sphincter (Sphincter cardiae). 

 The submucous coat is a layer of loose connective tissue which connects the 

 muscular and mucous coats; in it the vessels and nerves ramify before entering 

 the mucosa. 



