On The Parts Of Animals   

the other two; and it was this length which led nature to assign to
them their hard support, so as to ensure their straightness and
inflexibility; just as she has assigned to sanguineous animals their
bones or their fish-spines, as the case may be. To come now to
Insects. In these the arrangement is quite different from that of the
Cephalopods; quite different also from that which obtains in
sanguineous animals, as indeed has been already stated. For in an
insect there is no distinction into soft and hard parts, but the whole
body is hard, the hardness, however, being of such a character as to
be more flesh-like than bone, and more earthy and bone-like than
flesh. The purpose of this is to make the body of the insect less
liable to get broken into pieces.
Part 9
There is a resemblance between the osseous and the vascular systems;
for each has a central part in which it begins, and each forms a
continuous whole. For no bone in the body exists as a separate thing
in itself, but each is either a portion of what may be considered a
continuous whole, or at any rate is linked with the rest by contact
and by attachments; so that nature may use adjoining bones either as
though they were actually continuous and formed a single bone, or, for
purposes of flexure, as though they were two and distinct. And
similarly no blood-vessel has in itself a separate individuality; but
they all form parts of one whole. For an isolated bone, if such there
were, would in the first place be unable to perform the office for the
sake of which bones exist; for, were it discontinuous and separated
from the rest by a gap, it would be perfectly unable to produce either
flexure or extension; nor only so, but it would actually be injurious,
acting like a thorn or an arrow lodged in the flesh. Similarly if a
vessel were isolated, and not continuous with the vascular centre, it
would be unable to retain the blood within it in a proper state. For
it is the warmth derived from this centre that hinders the blood from
coagulating; indeed the blood, when withdrawn from its influence,
becomes manifestly putrid. Now the centre or origin of the
blood-vessels is the heart, and the centre or origin of the bones, in
all animals that have bones, is what is called the chine. With this
all the other bones of the body are in continuity; for it is the chine
that holds together the whole length of an animal and preserves its
straightness. But since it is necessary that the body of an animal
shall bend during locomotion, this chine, while it is one in virtue of
the continuity of its parts, yet its division into vertebrae is made
to consist of many segments. It is from this chine that the bones of
the limbs, in such animals as have these parts, proceed, and with it
they are continuous, being fastened together by the sinews where the
limbs admit of flexure, and having their extremities adapted to each
other, either by the one being hollowed and the other rounded, or by
both being hollowed and including between them a hucklebone, as a
connecting bolt, so as to allow of flexure and extension. For without
some such arrangement these movements would be utterly impossible, or
at any rate would be performed with great difficulty. There are some
joints, again, in which the lower end of the one bone and the upper
end of the other are alike in shape. In these cases the bones are
bound together by sinews, and cartilaginous pieces are interposed in
the joint, to serve as a kind of padding, and prevent the two
extremities from grating against each other.
Round about the bones, and attached to them by thin fibrous bands,
grow the fleshy parts, for the sake of which the bones themselves
exist. For just as an artist, when he is moulding an animal out of
clay or other soft substance, takes first some solid body as a basis,
and round this moulds the clay, so also has nature acted in fashioning
the animal body out of flesh. Thus we find all the fleshy parts, with
one exception, supported by bones, which serve, when the parts are
organs of motion, to facilitate flexure, and, when the parts are
motionless, act as a protection. The ribs, for example, which enclose
the chest are intended to ensure the safety of the heart and