i66 TEXT-BOOK OF PHYSIOLOGY 



diameter from n to 12 centimeters. The capacity of the stomach varies 

 from 1500 to 1700 c.c. In the empty condition its walls are contracted and 

 partly in contact, and the entire organ is drawn up into the upper part of 

 the abdominal cavity. The stomach being a contractile and distensible organ 

 adapts itself to varying amounts of food and hence continually varies in 

 size. The opening through which the food passes into the stomach is known 

 as the esophago-gastric or the cardiac orifice. The opening through which 

 it passes into the intestine is known as pylorus, the pyloric, or gastro-duodenal 

 orifice, indicated on the outer surface by a slight constriction known as the 

 gastro-duodenal constriction. Between these two orifices, the stomach, 

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

 larger curve, known as the lesser and greater curvatures respectively. Along 

 the lesser curvature there is a slight indentation due to a change in direction 

 of the right end of the stomach, known as the incisura angularis. If this 

 indentation is connected by a line with a point or angle almost opposite on 

 the greater curvature the stomach wilt be divided into a pyloric portion to the 

 right and a cardiac portion to the left. If a line be drawn transversely across 

 the stomach from the esophago-gastric or cardiac orifice to the greater curva- 

 ture, the cardiac portion will be subdivided into the fundus, to the extreme 

 left, and the cardiac portion proper or the body included between the fundus 

 and the pyloric portion. 



If a vertical section of the stomach is made, it will be observed that the 

 walls are extremely thin to the left but gradually increase in thickness in 

 passing toward the pyloric orifice. The cavity of the pyloric portion, is, 

 when the stomach is empty, subdivided into a vestibule and a pyloric canal 

 which latter is said to begin at a point opposite the sulcus intermedius, and 

 to extend to the pyloric orifice. The pyloric canal is narrow and cylindric 

 and measures from 2.5 to 3.5 centimeters. The vestibule and pyloric canal 

 when distended with food form a tubular region which has been termed the 

 antrum or the gastric canal. 



The Walls of the Stomach. 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 junction of the pyloric and cardiac regions, x-x, 

 Fig. 71, the circular fibers form a well-defined bundle the transverse band 

 which was supposed to contract periodically during digestion and thus par- 

 tially divide the stomach into two portions, the portion to the right of which 



