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. The teeth have one
invariable office, namely the reduction of food; but besides this
general function they have other special ones, and these differ in
different groups. Thus in some animals the teeth serve as weapons; but
this with a distinction. For there are offensive weapons and there are
defensive weapons; and while in some animals, as the wild Carnivora,
the teeth answer both purposes, in many others, both wild and
domesticated, they serve only for defence. In man the teeth are
admirably constructed for their general office, the front ones being
sharp, so as to cut the food into bits, and the hinder ones broad
and flat, so as to grind it to a pulp; while between these and
separating them are the dog-teeth, which, in accordance with the
rule that the mean partakes of both extremes, share in the
characters of those on either side, being broad in one part but
sharp in another. Similar distinctions of shape are presented by the
teeth of other animals, with the exception of those whose teeth are
one and all of the sharp kind. In man, however, the number and the
character even of these sharp teeth have been mainly determined by the
requirements of speech. For the front teeth of man contribute in
many ways to the formation of letter-sounds.
In some animals, however, the teeth, as already said, serve merely
for the reduction of food. When, besides this, they serve as offensive
and defensive weapons, they may either be formed into tusks, as for
instance is the case in swine, or may be sharp-pointed and interlock
with those of the opposite jaw, in which case the animal is said to be
saw-toothed
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