And it is necessary, if an animal is to obtain food after the
time of taking milk is over, that it should have instruments for the
treatment of the food. If, then, as Democritus says, this happened
about the time of reaching maturity, Nature would fail in something
possible for her to do. And, besides, the operation of Nature would be
contrary to Nature, for what is done by violence is contrary to
Nature, and it is by violence that he says the formation of the
first teeth is brought about. That this view then is not true is plain
from these and other similar considerations.
Now these teeth are developed before the flat teeth, in the first
place because their function is earlier (for dividing comes before
crushing, and the flat teeth are for crushing, the others for
dividing), in the second place because the smaller is naturally
developed quicker than the larger, even if both start together, and
these teeth are smaller in size than the grinders, because the bone of
the jaw is flat in that part but narrow towards the mouth. From the
greater part, therefore, must flow more nutriment to form the teeth,
and from the narrower part less.
The act of sucking in itself contributes nothing to the formation of
the teeth, but the heat of the milk makes them appear more quickly.
A proof of this is that even in suckling animals those young which
enjoy hotter milk grow their teeth quicker, heat being conducive to
growth.
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