Being rodents, they can have but two incisor teeth in each jaw, these
teeth being rootless, and so set in their sockets that they are
incessantly worn away in front, and as incessantly grow from the base,
take the curved form of their sockets, and act much like shears which
have the inestimable property of self-sharpening when blunted, and
self-renewal when chipped or actually broken off by coming against any
hard substance. Were the teeth to be without this power, the animal
would run a great risk of dying from hunger, the injured tooth not being
able either to do its own work, or to aid its companion of the opposite
jaw. Either tooth alone would be as useless as a single blade of a pair
of scissors.
There is another notable characteristic of these incisor teeth. If you
will examine the incisors of any rodent, whether it be a rat, a mouse, a
rabbit, or a beaver, you will see that the tips are "bevelled" off just
like the edge of a chisel. This shape is absolutely necessary to keep
the tooth in working order. How is this object to be attained?
In the solution of this problem we may see one of the many links which
connect art and nature.
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