The reason is that
this is useful for ease in creeping into holes, and for sitting upon
their eggs and guarding them. And as they are splayed outwards they
must of necessity tuck in their thighs and put them under them in
order to achieve the lifting of the whole body. In view of this they
cannot bend them otherwise than outwards.
16
We have already stated the fact that non-sanguineous animals with
limbs are polypods and none of them quadrupeds. And the reason why
their legs, except the extreme pairs, were necessarily attached
obliquely and had their flexions upwards, and the legs themselves were
somewhat turned under (bandy-shape) and backwards is plain. In all
such creatures the intermediate legs both lead and follow. If then
they lay under them, they must have had their flexion both forwards
and backwards; on account of leading, forwards; and on account of
following, backwards. Now since they have to do both, for this
reason their limbs are turned under and bent obliquely, except the two
extreme pairs. (These two are more natural in their movement, the
front leading and the back following.) Another reason for this kind of
flexion is the number of their legs; arranged in this way they would
interfere less with one another in progression and not knock together.
But the reason that they are bandy is that all of them or most of them
live in holes, for creatures living so cannot possibly be high above
the ground.
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