640 PHYSIOLOGY OF DIGESTION AND SECRETION. 



ture in its secreting glands. It is in this region that the hydro- 

 chloric acid of the gastric juice is mainly secreted. 



The Musculature of the Stomach. The musculature of the 

 stomach is usually divided into three layers, a longitudinal, an 

 oblique, and a circular coat. The longitudinal coat is continuous 

 at the cardia with the longitudinal fibers of the esophagus ; it spreads 

 out from this point along the length of the stomach, forming a layer 

 of varying thickness; along the curvatures the layer is stronger 

 than on the front and posterior surfaces, while at the pyloric end it 

 increases considerably in thickness, and passes over the pylorus to 

 be continued directly into the longitudinal coat of the duodenum. 

 The layer of oblique fibers is quite incomplete; it seems to be 

 continuous with the circular fibers of the esophagus, and spreads 

 out from the cardia for a certain distance over the front and posterior 

 surfaces of the fundus of the stomach, but toward the pyloric end 

 disappears, seeming to pass into the circular fibers. The circular 

 coat, which is placed between the two preceding layers, is the thick- 

 est and most important part of the musculature of the stomach. 

 At the fundus the circular bands are thin and somewhat loosely 

 placed, but toward the pyloric end they increase much in thickness, 

 forming a strong, muscular mass, which, as we shall see, plays the 

 most important part in the movements of the stomach. At the 

 pylorus itself a special development of this layer functions as a 

 sphincter pylori, which with the aid of a circular fold of the mucous 

 membrane makes it possible to shut off the duodenum completely 

 from the cavity of the stomach. The line of separation between 

 the antrum pylori and the body of the stomach is made by a 

 special thickening of the circular fibers which forms a structure 

 known as the "transverse band" by the older writers,* and de- 

 scribed more recentlyf as the "sphincter antri pylorici." 



The Movements of the Stomach. The solid food remains in 

 the stomach for several hours, and during this time the musculature 

 contracts in such a way that the thinner portions as they are formed 

 by digestion are ejected from time to time through the pylorus into 

 the intestine. Except at the definite intervals when the pyloric 

 sphincter relaxes the food is entirely shut off from the rest of the 

 alimentary canal by the tonic closure of the sphincters at the cardia 

 and the pylorus. There is a certain orderliness in the movements 

 of the stomach, and especially in the separation and ejection of the 

 more liquid from the solid parts, which shows the existence of a 

 specially adapted mechanism. These movements have been studied 

 by many investigators, making use of various experimental meth- 



* See Beaumont, " Physiology of Digestion, " second edition, 1847, p. 104. 

 f Hofmeister und Schiitz, " Archiv f . exper. Pathologic und Pharmakol- 

 ogie," 1886, vol. xx. 



