THE DIGESTIVE SYSTEM 



309 



greater curvature on the left side of the body and a lesser curvature to 

 the right. The opening of the esophagus into the stomach is the cardiac 

 orifice, that into the small intestine is the pylorus. 



The anterior more enlarged portion of the stomach is the cardiac 

 portion, the posterior more constricted portion is the pyloric portion. 

 In the cardiac division, may be distinguished a main body and a blind 

 pouch, the fundus. The pyloric portion of the stomach diminishes in 

 size towards the pylorus, which is reduced to a small aperture by a local 

 ring-like thickening of the mucous lining and of the layer of circular 



GREATER CURVATURE 



PYLORIC STOMACH 



Fig. 259. — The right half of the human stomach, viewed from within. 



Braus, after Elze.) 



(Redrawn from 



muscle. By this mechanism, only finely divided material is allowed to 

 pass in jets into the duodenum, forced by the peristalsis of the stomach. 



The wall of the stomach contains the same four layers of tissue as are 

 seen in the esophagus, plus an external serous layer. These beginning 

 with the outermost are the serosa, including the adventitia, the tunica 

 muscularis, tunica submucosa, and the tunica mucosa. The tunica 

 serosa is a connective tissue layer covered with the peritoneal epithelium. 

 In it are many blood vessels, with branches of the vagus nerve and the 

 celiac plexus of sympathetic nerve fibers. 



The tunica muscularis contains three layers of muscle, longitudinal, 

 circular, and obHque. By their combined action under the stimulus of 

 the sympathetic nerves, the stomach maintains a peristaltic churning 

 action as long as food is present. The tunica submucosa consists of loose 

 areolar connective tissue richly supplied with blood vessels and with a 



