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. As a remedy for this
Nature has given them a long ischium, and brought it to the centre
of the body, fixing it firmly; and she has placed the legs under
this central point, that the weight on either side may be equally
balanced, and standing or progression rendered possible. Such then
is the reason why a bird, though it is a biped, does not stand
erect. Why its legs are destitute of flesh has also already been
stated; for the reasons are the same as in the case of quadrupeds.
In all birds alike, whether web-footed or not, the number of toes in
each foot is four. For the Libyan ostrich may be disregarded for the
present, and its cloven hoof and other discrepancies of structure as
compared with the tribe of birds will be considered further on. Of
these four toes three are in front, while the fourth points
backward, serving, as a heel, to give steadiness. In the long-legged
birds this fourth toe is much shorter than the others, as is the
case with the Crex, but the number of their toes is not increased. The
arrangement of the toes is such as has been described in all birds
with the exception of the wryneck. Here only two of the toes are in
front, the other two behind; and the reason for this is that the
body of the wryneck is not inclined forward so much as that of other
birds. All birds have testicles; but they are inside the body. The
reason for this will be given in the treatise On the Generation of
Animals
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