HOW ANIMALS EAT. 



67 



Fig. 32.— Jaws and Pavement-teeth of a 

 Ray {Myliohates). 



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 Rays) 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 

 w r ith serrated edges, as in the 

 Shark; but more often like the 

 canines of Mammals, curved 

 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 cement 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, but 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, 



