Now as the front is more honourable and of
higher supremacy than the hinder aspect, so also and in like degree is
the great vessel superior to the aorta. For the great vessel is placed
in front, while the aorta is behind; the former again is plainly
visible in all sanguineous animals, while the latter is in some
indistinct and in some not discernible at all.
Lastly, the reason for the vessels being distributed throughout
the entire body is that in them, or in parts analogous to them, is
contained the blood, or the fluid which in bloodless animals takes the
place of blood, and that the blood or analogous fluid is the
material from which the whole body is made. Now as to the manner in
which animals are nourished, and as to the source from which they
obtain nutriment and as to the way in which they absorb this from
the stomach, these are matters which may be more suitably considered
and explained in the treatise on Generation. But inasmuch as the parts
are, as already said, formed out of the blood, it is but rational that
the flow of the blood should extend, as it does, throughout the
whole of the body. For since each part is formed of blood, each must
have blood about and in its substance.
To give an illustration of this. The water-courses in gardens are so
constructed as to distribute water from one single source or fount
into numerous channels, which divide and subdivide so as to convey
it to all parts; and, again, in house-building stones are thrown
down along the whole ground-plan of the foundation walls; because
the garden-plants in the one case grow at the expense of the water,
and the foundation walls in the other are built out of the stones.
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