Birds that have a long and a thick neck keep it stretched
out during flight; but those whose neck though long is slender fly
with it coiled up. For in this position it is protected, and less
likely to get broken, should the bird fly against any obstacle.
In all birds there is an ischium, but so placed and of such length
that it would scarcely be taken for an ischium, but rather for a
second thigh-bone; for it extends as far as to the middle of the
belly. The reason for this is that the bird is a biped, and yet is
unable to stand erect. For if its ischium extended but a short way
from the fundament, and then immediately came the leg, as is the
case in man and in quadrupeds, the bird would be unable to stand up at
all. For while man stands erect, and while quadrupeds have their heavy
bodies propped up in front by the forelegs, birds can neither stand
erect owing to their dwarf-like shape, nor have anterior legs to
prop them up, these legs being replaced by wings. 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.
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