HOW ANIMALS EAT. 61 
Fra. 24.—Mouth of the Crocodile: d, tongue; e, glands; f, inferior, and g, superior, 
valve, separating the cavity of the mouth from the throat, h. 
In the Toad, Frog, and Chameleon it is singularly exten- 
sile: 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. Snakes 
have a slender forked tongue, consisting of a pair of mus- 
cular cylinders, which is solely an instrument of touch. 
Birds are without lips or teeth, the jaws being covered 
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 cov- 
ered with a horny sheath, and generally spinous, its chief 
function being to secure the food when in the mouth. It 
is proportionally the largest and most fleshy in the Par- 
rots. 
The main characteristics of the mammalian mouth are 
fleshy lips and mobile cheeks.” In the duck-billed Mon- 
otremes lips are wanting, and in the Porpoises they are 
barely represented. But in the herbivorous quadrupeds 
