Moreover it cannot but necessarily be
that the more precise senses will have their precision rendered
still greater if ministered to by parts that have the purest blood.
For the motion of the heat of blood destroys sensory activity. For
these reasons the organs of the precise senses are lodged in the head.
It is not only the fore part of the head that is destitute of flesh,
but the hind part also. For, in all animals that have a head, it is
this head which more than any other part requires to be held up.
But, were the head heavily laden with flesh, this would be impossible;
for nothing so burdened can be held upright. This is an additional
proof that the absence of flesh from the head has no reference to
brain sensation. For there is no brain in the hinder part of the head,
and yet this is as much without flesh as is the front.
In some animals hearing as well as vision is lodged in the region of
the head. Nor is this without a rational explanation. For what is
called the empty space is full of air, and the organ of hearing is, as
we say, of the nature of air. Now there are channels which lead from
the eyes to the blood-vessels that surround the brain; and similarly
there is a channel which leads back again from each ear and connects
it with the hinder part of the head.
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