CHORDATA. 



333 



deer, etc.) there are four chambers in the stomach (Fig. 161). 

 The gastric glands produce an acid secretion which contains a 

 ferment acting chiefly on proteid foods. 



The food is retained in the stomach by means of a circular 

 (sphincter} muscle at its posterior end where it narrows into 

 the intestine. This latter portion is the principal digestive and 

 absorptive portion of the tract and varies much in length in 



FIG. 162. 



FIG. 162. Diagram of the stomach and oesophagus of the Fowl, o, oesophagus; c, 

 crop; p, proventriculus or glandular stomach; g, gizzard or grinding stomach; ; 

 intestine. 



Questions on the figure. Compare this figure with that of the 

 stomach of ruminants as to complexity. What are the functions of the 

 various portions? What changes take place in the gizzard of flesh-eating 

 birds if they are forced to live on grain? Why is the crop located outside 

 the cavity inclosed by the ribs? 



the various groups in accordance with the nature of the food 

 used, the vegetable feeders for the most part possessing the 

 longest intestines. Numerous circular or spiral folds of the 

 mucous membrane occur in the intestine. Special absorptive 

 organs (villi) supplied with blood and lymph vessels may 

 cover these folds. Near the anterior end the ducts of the liver 

 and pancreas open into the intestine. The liver is the largest 

 of the glands, and the pancreas one of the most important in 

 digestion. The intestine may open directly on the exterior 

 (most mammals), or into an epidermal pocket (cloaca) which 



