The skull is composed not of four
bones, but of six; two of these are in the region of the ears, small
in comparison with the other four. From the skull extend the jaws,
constituted of bone. (Animals in general move the lower jaw; the river
crocodile is the only animal that moves the upper one.) In the jaws is
the tooth-system; and the teeth are constituted of bone, and are
half-way perforated; and the bone in question is the only kind of bone
which it is found impossible to grave with a graving tool.
On the upper part of the course of the backbone are the
collar-bones and the ribs. The chest rests on ribs; and these ribs
meet together, whereas the others do not; for no animal has bone in
the region of the stomach. Then come the shoulder-bones, or
blade-bones, and the arm-bones connected with these, and the bones
in the hands connected with the bones of the arms. With animals that
have forelegs, the osseous system of the foreleg resembles that of the
arm in man.
Below the level of the backbone, after the haunch-bone, comes
the hip-socket; then the leg-bones, those in the thighs and those in
the shins, which are termed colenes or limb-bones, a part of which
is the ankle, while a part of the same is the so-called 'plectrum'
in those creatures that have an ankle; and connected with these
bones are the bones in the feet.
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