DIGESTION 



167 



was termed the antrum, and hence this transverse band has been termed the 

 sphincter antri pylorici. This function, however, has been questioned. 



In the pyloric region the circular fibers are more closely arranged, form- 

 ing thick well-defined rings termed the antral muscles. At the pyloric open- 

 ing the circular fibers are crowded together and form a distinct muscle band 

 known as the sphincter pylori which projects for some distance into the inte- 

 rior of the canal. It has been stated by Rudinger that the inner fibers of 

 the longitudinal coat become connected with this circular band and consti- 

 tute a distinct muscle, the dilatator pylori. The oblique fibers are most dis- 

 tinct 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 muscle tissue, the muscularis 

 mucosa, which supports the mucous membrane. 



The internal or mucous coat is loosely attached to the muscle 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. In passing from the cardiac 

 toward and into the pyloric region the mucous membrane becomes thicker 

 and forms the inner wall of the vestibule and pyloric canal. It finally be- 

 comes continuous with the mucous membrane of the intestine. At the pyloric 

 orifice there is a circular involution of the mucous membrane which is known 

 as the pyloric valve. This is strengthened by fibrous tissue and embraced 

 by the sphincter muscle previously described. 



Gastric Glands. The surface of the mucous membrane when examined 

 with a low magnifying power presents throughout innumerable depressions, 

 polygonal in shape and separated by slightly elevated ridges. At the bottom 

 of these spaces are to be seen small orifices, which are the mouths of the 

 glands embedded in the mucous membrane. A vertical section of the 

 gastric walls shows not only the position and the appearance of the 

 glands, but the relation of the various tissues which enter into the formation 

 of these walls. An examination of the mucous membrane in different 

 regions of the stomach reveals the presence of two distinct types of glands, 

 which from their situation are termed cardiac, and pyloric, which differ 

 not only in histologic structure, but also in function. Both types extend 

 through the entire thickness of the mucosa. 



The cardiac glands are formed by an involution of the basement mem- 

 brane of the mucosa and lined by epithelial cells. Each gland may be 

 said to consist of a short duct, or neck, and a body, or fundus (Fig. 72). 

 The latter portion is wavy or tortuous and frequently subdivided into as 

 many as four distinct and separate tubules. The duct is lined by columnar 

 epithelial cells similar to that covering the surface of the mucosa. The 

 lumen of the gland is bordered by epithelial cells, cuboid in shape and con- 

 sisting of a granular protoplasm containing a distinct sphencal nucleus. 

 These cells are generally spoken of as the chief or central cells. In addi- 



