HOW ANIMALS EAT. 
67 
fish (. Myxine ) has a single tooth on the roof of the mouth, 
and two serrated plates on the tongue; while the mouth 
of the Pike is crowded with teeth. In some we find 
teeth short and blunt, in the shape of cubes, or prisms, 
arranged like mosaic work. Such pavement-teeth (seen 
in some Rajs) are fitted for grinding sea-weed and crush¬ 
ing shell-fish. But the cone 
is the most common form: 
sometimes so slender and close 
as to resemble plush, as in the 
Perch; or of large size, and 
flattened like a spear - head 
with serrated edges, as in the 
Shark; but more often like the 
Fig. 32.— Jaws and Pavement-teeth of a 
canines of Mammals, curved Ray iMyUoUt^ 
inward to fit them for grappling. In the Shark, the 
teeth are confined to the fore-part of the mouth; in the 
Carp, they are all situated on the bones of the throat; in 
the Parrot-fish, they occupy both back and front; but in 
most Fishes the teeth are developed also on the roof, or 
palate, and, in fact, on nearly every bone in the mouth. 
They seldom appear (as in the Salmon) on the upper max¬ 
illary. As to mode of attachment, the teeth are generally 
anchylosed (fastened by bony matter) to the bones which 
support them, or simply bound by ligaments, as in the 
Shark. In a few Fishes, the teeth consist of flexible car¬ 
tilage ; but almost invariably they are composed of some 
kind of dentine, enamel and eement being absent. 
Of Amphibians and Reptiles, Toads, Turtles, and Tor¬ 
toises are toothless; Frogs have teeth in the upper jaw 
only; Snakes have a more complete set, blit Saurians pos¬ 
sess the most perfect dentition. The number is not fixed 
even in the same species: in the Alligator it varies from 
72 to 88. The teeth are limited to the jawbones in the 
higher forms (Saurians); but in others, as the Serpents, 
