On The Parts Of Animals   

a pulp in the mouth, the tongue very rarely gets caught between the
teeth; and, while the food is passing over the epiglottis seldom does
a particle of it slip into the windpipe.
The animals which have been mentioned as having no epiglottis owe this
deficiency to the dryness of their flesh and to the hardness of their
skin. For an epiglottis made of such materials would not admit of easy
motion. It would, indeed, take a longer time to shut down an
epiglottis made of the peculiar flesh of these animals, and shaped
like that of those with hairy skins, than to bring the edges of the
windpipe itself into contact with each other.
Thus much then as to the reason why some animals have an epiglottis
while others have none, and thus much also as to its use. It is a
contrivance of nature to remedy the vicious position of the windpipe
in front of the oesophagus. That position is the result of necessity.
For it is in the front and centre of the body that the heart is
situated, in which we say is the principle of life and the source of
all motion and sensation. (For sensation and motion are exercised in
the direction which we term forwards, and it is on this very relation
that the distinction of before and behind is founded.) But where the
heart is, there and surrounding it is the lung. Now inspiration, which
occurs for the sake of the lung and for the sake of the principle
which has its seat in the heart, is effected through the windpipe.
Since then the heart must of necessity lie in the very front place of
all, it follows that the larynx also and the windpipe must of
necessity lie in front of the oesophagus. For they lead to the lung
and heart, whereas the oesophagus leads to the stomach. And it is a
universal law that, as regards above and below, front and back, right
and left, the nobler and more honourable part invariably is placed
uppermost, in front, and on the right, rather than in the opposite
positions, unless some more important object stands in the way.
Part 4
We have now dealt with the neck, the oesophagus, and the windpipe, and
have next to treat of the viscera. These are peculiar to sanguineous
animals, some of which have all of them, others only a part, while no
bloodless animals have any at all. Democritus then seems to have been
mistaken in the notion he formed of the viscera, if, that is to say,
he fancied that the reason why none were discoverable in bloodless
animals was that these animals were too small to allow them to be
seen. For, in sanguineous animals, both heart and liver are visible
enough when the body is only just formed, and while it is still
extremely small. For these parts are to be seen in the egg sometimes
as early as the third day, being then no bigger than a point; and are
visible also in aborted embryos, while still excessively minute.
Moreover, as the external organs are not precisely alike in all
animals, but each creature is provided with such as are suited to its
special mode of life and motion, so is it with the internal parts,
these also differing in different animals. Viscera, then, are peculiar
to sanguineous animals; and therefore are each and all formed from
sanguineous material, as is plainly to be seen in the new-born young
of these animals. For in such the viscera are more sanguineous, and of
greater bulk in proportion to the body, than at any later period of
life, it being in the earliest stage of formation that the nature of
the material and its abundance are most conspicuous. There is a heart,
then, in all sanguineous animals, and the reason for this has already
been given. For that sanguineous animals must necessarily have blood
is self-evident. And, as the blood is fluid, it is also a matter of
necessity that there shall be a receptacle for it; and it is
apparently to meet this requirement that nature has devised the
blood-vessels. These, again, must necessarily have one primary source.
For it is preferable that there shall be one such, when possible,
rather than several. This primary source of the vessels is the heart.
For the vessels manifestly issue from it and do not go through it.
Moreover, being as it is homogeneous, it has the character of a
blood-vessel. Again its position is that of a primary or dominating