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Aristotle - On The Parts Of Animals
Atec Февраль 16 2008 20:01:06
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Of the two separate portions which constitute the head, namely the
upper part and the lower jaw, the latter in man and in the
viviparous quadrupeds moves not only upwards and downwards, but also
from side to side; while in fishes, and birds and oviparous
quadrupeds, the only movement is up and down. The reason is that
this latter movement is the one required in biting and dividing
food, while the lateral movement serve to reduce substances to a pulp.
To such animals, therefore, as have grinder-teeth this lateral
motion is of service; but to those animals that have no grinders it
would be quite useless, and they are therefore invariably without
it. For nature never makes anything that is superfluous. While in
all other animals it is the lower jaw that is movable, in the river
crocodile it is exceptionally the upper. This is because the feet in
this creature are so excessively small as to be useless for seizing
and holding prey; on which account nature has given it a mouth that
can serve for these purposes in their stead. For that direction of
motion which will give the greater force to a blow will be the more
serviceable one in holding or in seizing prey; and a blow from above
is always more forcible than one from below. Seeing, then, that both
the prehension and the mastication of food are offices of the mouth,
and that the former of these two is the more essential in an animal
that has neither hands nor suitably formed feet, these crocodiles will
derive greater benefit from a motion of the upper jaw downwards than
from a motion of the lower jaw upwards
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