274 



BIRDS 



on to the stomach the food is fui-tlier acted on b}' the diges- 

 tive juices of this oi'gan. In the gizzard the food is masti- 

 cated, as it were, and Jiiore thoroughly mixed ¥.'ith the 

 cUgestive juices tricl<ling uito the gizzard from tlie stomach. 

 In the absence of teeth, pebbles are swallowed and retained 



Caecum 

 Intestine' 

 Pancrecib 



Liver 



Breastbone 



I i( 1S7 — Intciual struf tiire of a bird. 



in the gizzard to aid that oi'gan in reducing the food. 

 In the duodenum the footl receives the final digestive 

 ingredients, the bile from the liver and the pancreatic 

 juice. 



The circulatory system. — The lieart of the sparrow is 

 four chandjei'ed and the l(>ft side is completely separated 

 from the right side; therefore tliei'e is a doul)le circulation, 

 that is, one set of l)lood ^'(■ssels carrying impure (venous) 

 blood and another set cai'i'ving pui'c (arterial) blood. 

 Birds are very active animals, ant! the circulation is much 



