74 ANATOMY OF THE RAT 



gions are sharply separated by the horny boundary fold, 

 which extends ventrodextrad, on the anterior and poster- 

 ior surfaces, from the vicinity of the cardia. The wall of 

 the cardiac sac is opaque in an empty stomach, and its 

 inner surface is extensively folded. The esophagus opens 

 into the cardiac sac, for it lies at the base of the tongue-like 

 dextral extension of the sac's horny lining. The part 

 of the boundary fold bordering the right end of this exten- 

 sion is highly sinuous. 



Food passes to the small intestine through the pylorus, 

 at the upper right hand extremity of the stomach. The 

 pylorus contains a ring of muscle whose contraction closes 

 the digestive tube, shutting off communication between the 

 stomach and intestine. It regulates in this manner the 

 passage of food from the stomach to intestine. The posi- 

 tion of the pylorus is indicated externally by a groove 

 around the alimentary canal. Internally the high ridges 

 in the glandular part of the stomach are replaced at, or 

 slightly to the right of, the pylorus by the velvety surface 

 of the small intestine. 



The stomach wall of the mouse (and rat also) are said 

 to show the following structures. There are two muscle 

 layers, a thick circular and a thinner longitudinal layer. 

 The cardiac sac and boundary fold are lined internally by 

 the statum corneum, or horny layer of epithelial cells. 

 There are three zones in the glandular tissue at the right 

 of the boundary fold. The cardial glands surround the 

 tongue-like extension of the horny epithelium at the right 

 of the cardia, and extend ventrally along the anterior and 

 posterior walls. The rennet glands are on the ventral wall 

 at the right of the boundary fold. The pyloric gland region 

 lies between the pylorus, and the cardial and rennet glands. 

 The glands of the mammalian stomach secrete the gastric 

 juice which initiates the digestion of protein substances in 



