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. This consumption of the earthy matter on the hoof
explains why these animals, as a rule, have no huckle-bones; a
second reason being that the presence of such a bone in the joint of
the hind leg somewhat impedes its free motion. For extension and
flexion can be made more rapidly in parts that have but one angle than
in parts that have several. But the presence of a huckle-bone, as a
connecting bolt, is the introduction as it were of a new
limb-segment between the two ordinary ones. Such an addition adds to
the weight of the foot, but renders the act of progression more
secure. Thus it is that in such animals as have a hucklebone, it is
only in the posterior and not in the anterior limbs that this bone
is found. For the anterior limbs, moving as they do in advance of
the others, require to be light and capable of ready flexion,
whereas firmness and extensibility are what are wanted in the hind
limbs. Moreover, a huckle-bone adds weight to the blow of a limb,
and so renders it a suitable weapon of defence; and these animals
all use their hind legs to protect themselves, kicking out with
their heels against anything which annoys them. In the cloven-hoofed
quadrupeds the lighter character of the hind legs admits of there
being a huckle-bone; and the presence of the huckle-bone prevents them
from having a solid hoof, the bony substance remaining in the joint,
and therefore being deficient in the foot
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