QUADRUPEDS. 
339 
altogether destitute of canines, and their incisors, which are 
separated by a great blank space from the molars, are 
furnished with enamel only 
on one side. They project 
from the front of each jaw in 
a curve; and, as they have 
no roots, but spring from a 
pulpy germ deeply embedded 
in their sockets, they are skuUofRodeut. 
continually growing. These peculiarities have a direct 
relation to the habits of the animals; for they live 
upon food, usually hard and solid, which they gnaw 
away atom by atom, with the tips of these projecting 
teeth. For this work it is needful that the tips of the 
teeth, which meet and play upon each other, should have 
a sharp chisel-like edge, and this result follows from the 
provision above mentioned, that the hard enamel is con- 
fined to the front side of the tooth ; the bony portion of 
the tip, being soft, wears away more rapidly than the 
enamel of the front, which thus always presents a sharp 
cutting edge. The constant growth, too, just balances the 
ordinary wear of the teeth in eating, so that they are main- 
tained in constant opposibility to each other. The perfec- 
tion of this balance becomes manifest, when, by accident, 
one of the incisor teeth is lost; for, in this case, the oppo- 
site tooth, having no wear, grows out to a monstrous length, 
maintaining its original curve throughout, and becomes a 
tusk, which in time presents a bar to the reception of food, 
and death by starvation ensues. 
Strange as it may be thought, there is an affinity by no 
means obscure, between these minute animals and the 
