3IO 



COMPARATIVE ANATOMY 



plexus of sympathetic nerve fibers. The mucosa is divided into a mucous 

 columnar epithelium, a tunica propria, and a muscularis mucosae contain- 

 ing circular and longitudinal muscle fibers. The tunica propria includes 

 considerable adenoid tissue. 



The simple mucous epithehum which lines the stomach joins abruptly 

 the stratified epithehum of the esophagus. Viewed with a hand-lens, 

 the inner surface of the stomach appears to be filled with minute pores, 

 which are the apertures of the ducts of the gastric glands. Three kinds of 

 stomach glands are distinguished, cardiac, gastric, and pyloric. The 



"MUCOUS EPITHEUUM-' 



"GASTRIC P1T< 



HIEF CELLS 



.PARIETAL CELLS 



MUSCULARIS'. 



'Fig. 260. — Cross sections of the wall of the human stomach, showing A, the struc- 

 ture of the gastric (fundus) glands, and B, that of the pyloric glands. While the secre- 

 tions of gastric glands are chiefly digestive (gastric juice), the pyloric glands secrete 

 mucus chiefly. (Redrawn after Braus.) 



cardiac glands occupy a relatively small area near the cardiac orifice 

 and resemble closely the glands of the esophagus. Each cardiac gland 

 consists of a group of parallel tubules opening into a single duct or pit. 

 The walls of the tubules are formed of cells which secrete zymogen or 

 pepsinogen granules, of parietal cells which secrete the chemical precursor 

 of hydrochloric acid, and of mucus-secreting cells. 



Most of the glands of the stomach are gastric each of which, Uke the 

 cardiac glands, consists of a duct or pit connected with a group of straight 

 or slightly curved tubules. During life, the number of pits is multipUed, 

 while the number of tubules connected with each crypt is correspondingly 

 reduced. The pits are relatively short and are lined with mucous gland 

 cells hke those which cover the inner surface of the stomach, while the 



