432 APPLIED BIOLOGY 



who are interested should take the first opportunity to 

 examine the chief organs in a chicken or other large bird 

 which is being prepared for cooking. 



The alimentary canal is essentially the same in all birds. 

 Existing birds have no teeth, but some fossil forms had them. 

 The tongue is sometimes specially adapted for seizing food 

 (e.g., insect-catchers). The esophagus often has a crop for 

 storage of food. The muscular stomach (called gizzard) has 

 walls whose strength varies with the food (strong in grami- 

 nivorous birds). It contains small stones which the bird has 

 swallowed to aid in grinding the food. From the stomach 

 there is a coiled intestine into which a liver and a pancreas 

 pour their secretions. The posterior part of the intestine is 

 expanded into a cloaca, into which the ducts from kidneys 

 and from the reproductive organs open. 



The respiratory organs are very peculiar. The voice- 

 organ is not in the larynx, as in mammals, but is lower down 

 on the trachea or "wind-pipe. This voice-organ (also called 

 syrinx) is a complicated structure, especially in singing birds. 

 Large air-cavities in the bird's body, and even in the bones 

 of some, are connected with the bronchial tubes leading from 

 the trachea. In fact, when a bird breathes by dilating its 

 thorax and abdomen, a -large part of the air inhaled rushes 

 into air-sacs and very little distention of the lungs occurs 

 as in mammals. This peculiar mechanism is a more efficient 

 respiratory apparatus than lungs of mammals, and the oxy- 

 gen-supply to the blood is more complete. This more rapid 

 respiration is necessary because of the great activity of birds, 

 especially in flying and in singing. 



Another remarkable fact connected with the respiratory 

 organs is that their great surface eliminates excretory water 

 and excess heat. In mammals, this is accomplished by the 

 kidneys and sweat-glands ; but bird kidneys do not eliminate 

 much water, and they have no sweat-glands in their skin. 



As a result of the intense respiration and consequent 



