156 



DIGESTION IN THE LOWEE ANIMALS 



/ 

 9 



until needed bj^ the bcrdy. By means of this organ the 

 bird is enabled to eat enough at one meal to last for some 



time. Succeeding 

 this is a compart- 

 ment called the giz- 

 zard. "WTien food is 

 needed it is passed 

 from the crop into 

 this gizzard which has 

 an outer wall of thick 

 muscles and an inner 

 horny lining. Inside 

 it, too, are stones and 

 other hard objects 

 which the bird swal- 

 lows for the purpose 

 of grinding the food 

 thoroughly to pre- 

 pare it for the ac- 

 tion of the digestive 

 fluids. A¥hen thor- 

 oughly ground up, 

 the food passes into 

 the third compart- 

 ment, or true diges- 

 tive stomach, where 

 the gastric juice is 

 secreted. 



The ruminants or 

 cud-chewing animals 

 show still another cin"ious modification. In these animals, 

 such as the cow, the stomach is divided into four compart- 



FiG. 56 — Digestive tract of a bird ; o, esophagus ; 

 6, crop ; c, proven triculus ; d, gizzard ; e, liver ; 

 /, gall bladder ; y, pancreas ; h, duodenum ; 

 i, small intestine ; k, c^ca ; m, ureter ; n, 

 oviduct ; o, cloaca. 



