98 



GENERAL ZOOLOGY 



cularis is well developed. The mucosa receives the openings of 

 tubular glands of two general types, cardiac and pyloric, of which 

 the cardiac glands possess the greater number of granular cells. 

 Experiments indicate that the pepsin content of the stomach wall 

 is greatest in the cardiac portion, from which it is inferred that 

 the pepsin is formed by the granular cells. Hydrochloric acid 

 is produced in the stomach and gives its contents an acid reaction. 

 In a bird such as the domestic fowl the stomach consists of 

 two distinct regions: an anterior glandular part, the proven- 

 triculus, and a highly muscular posterior part, the gizzard (Fig. 

 64). The glands of the proventriculus produce a digestive 



Fig. 65. — Diagram of ruminant stomach, the dotted line showing the course 

 of the food, a, abomasum; oe, esophagus; p, pylorus; ps, psalterium (omasum, 

 manyplies); rt, reticulum (honeycomb); ru, rumen (paunch). {From Kingsley, 

 Comparative Anatomy of Vertebrates, P. Blakistons Son and Company. By 

 permission.) 



secretion that is mixed with the food before it enters the gizzard 

 where it is ground up. In the absence of teeth the gizzard of 

 grain-eating birds serves as an organ of mastication, to which 

 end it is adapted by having thick muscular walls lined with a 

 tough, horny membrane. The process of trituration is facilitated 

 in such birds by small pebbles or other gritty material, swallowed 

 with the food. The gizzard is less well developed in purely 

 carnivorous birds, whose food is of a softer consistency. 



The stomach of a ruminant, like the ox, also shows rather 

 striking departures from the common type of vertebrate stomach. 

 In this case the stomach region consists of four parts; (1) the 

 rumen or paunch; (2) the reticulum or honeycomb; (3) the psalter- 

 ium; and (4) the abomasum. Of these, the first two divisions 

 seem to be modifications of the lower end of the esophagus in 



