164 TEXT-BOOK OF PHYSIOLOGY. 



border presents a curve and along its lower border a much larger curve, 

 known as the lesser and greater curvatures respectively. The extreme left 

 end of the stomach is termed the fundus. Toward the pyloric orifice there 

 is a region of the stomach included between the pylorus and a line uniting a 

 small indentation on the lesser curvature with a point or angle almost oppo- 

 site on the greater curvature, known as the antrum. The region included 

 between the ill-defined limits of the fundus and the antrum is known as 

 the preantral or cardiac region. 



The walls of the stomach are formed by four distinct coats united by 

 areolar tissue and named, from without inward, as the serous, muscle, 

 submucous, and mucous. 



The external or serous coat is thin and transparent and formed by a 

 reduplication of the general peritoneal membrane. 



The middle or muscle coat consists of three layers of non-striated muscle- 

 fibers, named from their direction the longitudinal, circular, and oblique. 

 The longitudinal fibers are most abundant along the lesser curvature 

 and are a continuation of those of the esophagus; over the remainder of 

 the stomach they are thinly scattered, but toward the pyloric orifice they 

 are more numerous and form a tolerably thick layer which becomes con- 

 tinuous with the fibers of the small intestine. The circular fibers form a 

 complete layer encircling the entire organ, with the exception, perhaps, of a 

 portion of the fundus. The fibers of this coat cross the longitudinal fibers 

 at right angles. At the lower end of the esophagus and surrounding the 

 cardia the circular muscle fibers form a true sphincter which is known as 

 the sphincter cardia. At the juntion of the antrum with the preantral region 

 the circular fibers are arranged in a well-defined bundle termed the sphincter 

 antri pylorici. In the pyloric region the circular fibers are more closely 

 arranged, forming thick well-defined rings termed the antral muscles. At 

 the pyloric opening the circular fibers are again crowded together and 

 form a distinct muscle band the sphincter pylori which projects for some 

 distance into the interior of the stomach. It has been stated by Riidinger 

 that the inner fibers of the longitudinal coat become connected with this 

 circular band and constitute a distinct muscle, the dilatator pylori. The 

 oblique fibers are most distinct over the cardiac portion of the stomach, 

 but extend from left to right as far as the junction of the middle and last 

 thirds of the stomach. They are continuations of the circular fibers of the 

 esophagus. 



The submucous coat consists of loose areolar tissue carrying blood-vessels, 

 nerves, and lymphatics. It serves to unite the muscle to the mucous 

 coat. Its inner surface bears a thin layer of muscular tissue, the muscularis 

 mucoscB, which supports the mucous membrane. 



The internal or mucous coat is loosely attached to the muscular coat. In 

 the empty and contracted state of the stomach it is thrown into longitudinal 

 folds, or rugae, which are, however, obliterated when the organ is distended 

 with food. The mucous membrane in adult life is smooth and velvety in 

 appearance, gray in color, and covered with a layer of mucus. Its average 

 thickness is about one millimeter. The surface of the membrane is covered 

 with a layer of columnar epithelial cells. At the pylorus there is a circular 

 involution of the mucous membrane which is known as the pyloric valve. 



