HOW ANIMALS EAT 263 



is singularly extensile ; rooted in front and free behind, 

 it is shot from the mouth with such rapidity that the 

 insect is seized and swallowed more quickly than the 

 eye can follow. The chameleon's tongue is also exten- 

 sile. Snakes have a slender forked tongue, consisting 

 of a pair of muscular cylinders, which is solely an in- 

 strument of touch. 



FlG. 224. Mouth of the Crocodile: d, tongue; e, glands; _/", inferior, and g, superior, 

 valve, separating the cavity of the mouth from the throat, h. 



Birds are without lips or teeth, the jaws being cov- 

 ered with horn forming a beak. This varies greatly 

 in shape, being extremely wide in the whip-poor-will, 

 remarkably long in the pelican, stout in the eagle, and 

 slender in the hummer. It is hardest in those that tear 

 or bruise their food, and softest in water birds. The 

 tongue is also covered with a horny sheath, and is gen- 

 erally spinous, its chief function being to secure the 

 food when in the mouth. It is proportionally largest 

 and most fleshy in the parrots. 



The main characteristics of the mammalian mouth 

 are flesh lips and mobile cheeks. 77 In the duck-billed 



