On The Parts Of Animals   

into a compound whole, but is rather, as already said, the result of a
joint-like division. These jointings are most distinct in animals of
keen sensibility, and less so in those that are of duller feeling, in
swine for instance. Different hearts differ also from each other in
their sizes, and in their degrees of firmness; and these differences
somehow extend their influence to the temperaments of the animals. For
in animals of low sensibility the heart is hard and dense in texture,
while it is softer in such as are endowed with keener feeling. So also
when the heart is of large size the animal is timorous, while it is
more courageous if the organ be smaller and of moderate bulk. For in
the former the bodily affection which results from terror already
pre-exists; for the bulk of the heart is out of all proportion to the
animal's heat, which being small is reduced to insignificance in the
large space, and thus the blood is made colder than it would otherwise
be.
The heart is of large size in the hare, the deer, the mouse, the
hyena, the ass, the leopard, the marten, and in pretty nearly all
other animals that either are manifestly timorous, or betray their
cowardice by their spitefulness.
What has been said of the heart as a whole is no less true of its
cavities and of the blood-vessels; these also if of large size being
cold. For just as a fire of equal size gives less heat in a large room
than in a small one, so also does the heat in a large cavity or a
large blood-vessel, that is in a large receptacle, have less effect
than in a small one. Moreover, all hot bodies are cooled by motions
external to themselves, and the more spacious the cavities and vessels
are, the greater the amount of spirit they contain, and the more
potent its action. Thus it is that no animal that has large cavities
in its heart, or large blood-vessels, is ever fat, the vessels being
indistinct and the cavities small in all or most fat animals.
The heart again is the only one of the viscera, and indeed the only
part of the body, that is unable to tolerate any serious affection.
This is but what might reasonably be expected. For, if the primary or
dominant part be diseased, there is nothing from which the other parts
which depend upon it can derive succour. A proof that the heart is
thus unable to tolerate any morbid affection is furnished by the fact
that in no sacrificial victim has it ever been seen to be affected
with those diseases that are observable in the other viscera. For the
kidneys are frequently found to be full of stones, and growths, and
small abscesses, as also are the liver, the lung, and more than all
the spleen. There are also many other morbid conditions which are seen
to occur in these parts, those which are least liable to such being
the portion of the lung which is close to the windpipe, and the
portion of the liver which lies about the junction with the great
blood-vessel. This again admits of a rational explanation. For it is
in these parts that the lung and liver are most closely in communion
with the heart. On the other hand, when animals die not by sacrifice
but from disease, and from affections such as are mentioned above,
they are found on dissection to have morbid affections of the heart.
Thus much of the heart, its nature, and the end and cause of its
existence in such animals as have it.
Part 5
In due sequence we have next to discuss the blood-vessels, that is to
say the great vessel and the aorta. For it is into these two that the
blood first passes when it quits the heart; and all the other vessels
are but offshoots from them. Now that these vessels exist on account
of the blood has already been stated. For every fluid requires a
receptacle, and in the case of the blood the vessels are that
receptacle. Let us now explain why these vessels are two, and why they
spring from one single source, and extend throughout the whole body.
The reason, then, why these two vessels coalesce into one centre, and
spring from one source, is that the sensory soul is in all animals
actually one; and this one-ness of the sensory soul determines a
corresponding one-ness of the part in which it primarily abides. In