THE STOMACH 137 



At the termination in the stomach, the circular fibers are most 

 numerous, forming the cardiac sphincter which prevents the return 

 of stomach contents. 



The remaining organs of digestion are contained in the ab- 

 dominal cavity, which is lined with a serous sac or membrane 

 called peritoneum (see p. 367). These organs are developed from 

 an original straight tube behind the peritoneum. Therefore, 

 as they grow, they press forward against it and get a covering 

 which is called their serous layer. Their muscular coats are all 

 involuntary or unstriped muscle. 



THE STOMACH 



The stomach (gaster, Fig. 104) is in the epigastric region of the 

 abdomen just below the diaphragm. Shape and size: like a 

 curved flask, ten to twelve inches long and six to eight wide at 

 the larger end, which is turned toward the left side. Average 

 capacity: five pints in distention ; two pints when moderately filled. 



The stomach has two surfaces, two borders, two orifices and two 

 extremities cardiac and pyloric, with a pre-pyloric part between 

 them. 



The surfaces are the anterior looking slightly upward; and the 

 posterior looking slightly downward. 



The borders are usually called curvatures; the upper border is 

 the lesser curvature (about five inches in length) ; the lower border is 

 the greater curvature (about twenty inches in length). 



The left extremity is the expanded portion called the tundus of 

 the stomach (also the greater cul-de-sac), and the cardiac end (from 

 its nearness to the heart). 



The right extremity is called the pyloric extremity. It is just 

 below the liver. 



The orifices are at the extremities. At the left is the esopha- 

 geal orifice, guarded by the sphincter of the cardia; at the right 

 is the pyloric orifice, guarded by the sphincter of the pylorus or 

 "gate-keeper." 



The coats or tunics of the stomach are four in number 

 mucous, submucous, muscular, and serous. 



The mucous layer, or mucosa, is the innermost layer. It is 

 pink in color but becomes bright red when food is present, from the 

 increased blood-supply necessary for digestion. It lies in folds, or 



