gazelle. But in all our speculations concerning nature, what we have
to consider is the general rule; for that is natural which applies
either universally or generally. And thus when we say that the largest
animals have most earthy matter, we say so because such is the general
rule. Now this earthy matter is used in the animal body to form
bone. But in the larger animals there is an excess of it, and this
excess is turned by nature to useful account, being converted into
weapons of defence. Part of it necessarily flows to the upper
portion of the body, and this is allotted by her in some cases to
the formation of tusks and teeth, in others to the formation of horns.
Thus it is that no animal that has horns has also front teeth in
both jaws, those in the upper jaw being deficient. For nature by
subtracting from the teeth adds to the horns; the nutriment which in
most animals goes to the former being here spent on the augmentation
of the latter. Does, it is true, have no horns and yet are equally
deficient with the males as regards the teeth. The reason, however,
for this is that they, as much as the males, are naturally
horn-bearing animals; but they have been stripped of their horns,
because these would not only be useless to them but actually
baneful; whereas the greater strength of the males causes these
organs, though equally useless, to be less of an impediment. In
other animals, where this material is not secreted from the body in
the shape of horns, it is used to increase the size of the teeth; in
some cases of all the teeth, in others merely of the tusks, which thus
become so long as to resemble horns projecting from the jaws.
So much, then, of the parts which appertain to the head.
3
Below the head lies the neck, in such animals as have one. This is
the case with those only that have the parts to which a neck is
subservient. These parts are the larynx and what is called the
oesophagus. Of these the former, or larynx, exists for the sake of
respiration, being the instrument by which such animals as breathe
inhale and discharge the air. Therefore it is that, when there is no
lung, there is also no neck. Of this condition the Fishes are an
example. The other part, or oesophagus, is the channel through which
food is conveyed to the stomach; so that all animals that are
without a neck are also without a distinct oesophagus; Such a part
is in fact not required of necessity for nutritive purposes; for it
has no action whatsoever on the food. Indeed there is nothing to
prevent the stomach from being placed directly after the mouth.
This, however, is quite impossible in the case of the lung. For
there must be some sort of tube common to the two divisions of the
lung, by which--it being bipartite--the breath may be apportioned to
their respective bronchi, and thence pass into the air-pipes; and such
an arrangement will be the best for giving perfection to inspiration
and expiration. The organ then concerned in respiration must of
necessity be of some length; and this, again, necessitates there being
an oesophagus to unite mouth and stomach. This oesophagus is of a
flesh-like character, and yet admits of extension like a sinew. This
latter property is given to it, that it may stretch when food is
introduced; while the flesh-like character is intended to make it soft
and yielding, and to prevent it from being rasped by particles as they
pass downwards, and so suffering damage. On the other hand, the
windpipe and the so-called larynx are constructed out of a
cartilaginous substance. For they have to serve not only for
respiration, but also for vocal purposes; and an instrument that is to
produce sounds must necessarily be not only smooth but firm. The
windpipe lies in front of the oesophagus, although this position
causes it to be some hindrance to the latter in the act of
deglutition. For if a morsel of food, fluid or solid, slips into it by
accident, choking and much distress and violent fits of coughing
ensue. This must be a matter of astonishment to any of those who
assert that it is by the windpipe that an animal imbibes fluid. For
the consequences just mentioned occur invariably, whenever a
particle of food slips in, and are quite obvious. Indeed on many
grounds it is ridiculous to say that this is the channel through which
animals imbibe fluid. For there is no passage leading from the lung to
the stomach, such as the oesophagus which we see leading thither
from the mouth. Moreover, when any cause produces sickness and
vomiting, it is plain enough when the fluid is discharged. It is
manifest also that fluid, when swallowed, does not pass directly
into the bladder and collect there, but goes first into the stomach.
For, when red wine is taken, the dejections of the stomach are seen to
be coloured by its dregs; and such discoloration has been even seen on
many occasions inside the stomach itself, in cases where there have
been wounds opening into that organ. However, it is perhaps silly to
be minutely particular in dealing with silly statements such as this.
The windpipe then, owing to its position in front of the oesophagus,
is exposed, as we have said, to annoyance from the food. To obviate
this, however, nature has contrived the epiglottis. This part is not
found in all sanguineous animals, but only in such of them as have a
lung; nor in all of these, but only in such as at the same time have
their skin covered with hairs, and not either with scaly plates or
with feathers. In such scaly and feathered animals there is no
epiglottis, but its office is supplied by the larynx, which closes and
opens, just as in the other case the epiglottis falls down and rises
up; rising up during the ingress or egress of breath, and falling down
during the ingestion of food, so as to prevent any particle from
slipping into the windpipe. Should there be the slightest want of
accuracy in this movement, or should an inspiration be made during the
ingestion of food, choking and coughing ensue, as already has been
noticed. So admirably contrived, however, is the movement both of
the epiglottis and of the tongue, that, while the food is being ground
to 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.
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 part. For
nature, when no other more important purpose stands in her way, places
the more honourable part in the more honourable position; and the
heart lies about the centre of the body, but rather in its upper
than its lower half, and also more in front than behind. This is
most evident in the case of man, but even in other animals there is
a tendency in the heart to assume a similar position, in the centre of
the necessary part of the body, that is to say of the part which
terminates in the vent for excrement. For the limbs vary in position
in different animals, and are not to be counted with the parts which
are necessary for life. For life can be maintained even when they
are removed; while it is self-evident that the addition of them to
an animal is not destructive of it.
There are some who say that the vessels commence in the head. In
this they are clearly mistaken. For in the first place, according to
their representation, there would be many sources for the vessels, and
these scattered; and secondly, these sources would be in a region that
is manifestly cold, as is shown by its intolerance of chill, whereas
the region of the heart is as manifestly hot. Again, as already
said, the vessels continue their course through the other viscera, but
no vessel spreads through the heart. From this it is quite evident
that the heart is a part of the vessels and their origin; and for this
it is well suited by its structure. For its central part consists of a
dense and hollow substance, and is moreover full of blood, as though
the vessels took thence their origin. It is hollow to serve for the
reception of the blood, while its wall is dense, that it may serve
to protect the source of heat. For here, and here alone in all the
viscera and indeed in all the body, there is blood without
blood-vessels, the blood elsewhere being always contained within
vessels. Nor is this but consistent with reason. For the blood is
conveyed into the vessels from the heart, but none passes into the
heart from without. For in itself it constitutes the origin and
fountain, or primary receptacle, of the blood. It is however, from
dissections and from observations on the process of development that
the truth of these statements receives its clearest demonstration. For
the heart is the first of all the parts to be formed; and no sooner is
it formed than it contains blood. Moreover, the motions of pain and
pleasure, and generally of all sensation, plainly have their source in
the heart, and find in it their ultimate termination. This, indeed,
reason would lead us to expect. For the source must, when. ever
possible, be one; and, of all places, the best suited for a source
is the centre. For the centre is one, and is equally or almost equally
within reach of every part. Again, as neither the blood itself, nor
yet any part which is bloodless, is endowed with sensation, it is
plain that that part which first has blood, and which holds it as it
were in a receptacle, must be the primary source of sensation. And
that this part is the heart is not only a rational inference, but also
evident to the senses. For no sooner is the embryo formed, than its
heart is seen in motion as though it were a living creature, and
this before any of the other parts, it being, as thus shown, the
starting-point of their nature in all animals that have blood. A
further evidence of the truth of what has been stated is the fact that
no sanguineous animal is without a heart. For the primary source of
blood must of necessity be present in them all. It is true that
sanguineous
animals not only have a heart but also invariably have a
liver. But no one could ever deem the liver to be the primary organ
either of the whole body or of the blood. For the position in which it
is placed is far from being that of a primary or dominating part; and,
moreover, in the most perfectly finished animals there is another
part, the spleen, which as it were counterbalances it. Still
further, the liver contains no spacious receptacle in its substance,
as does the heart; but its blood is in a vessel as in all the other
viscera. The vessel, moreover, extends through it, and no vessel
whatsoever originates in it; for it is from the heart that all the
vessels take their rise. Since then one or other of these two parts
must be the central source, and since it is not the liver which is
such, it follows of necessity that it is the heart which is the source
of the blood, as also the primary organ in other respects. For the
definitive characteristic of an animal is the possession of sensation;
and the first sensory part is that which first has blood; that is to
say is the heart, which is the source of blood and the first of the
parts to contain it.
The apex of the heart is pointed and more solid than the rest of the
organ. It lies against the breast, and entirely in the anterior part
of the body, in order to prevent that region from getting chilled. For
in all animals there is comparatively little flesh over the breast,
whereas there is a more abundant covering of that substance on the
posterior surface, so that the heat has in the back a sufficient
amount of protection. In all animals but man the heart is placed in
the centre of the pectoral region; but in man it inclines a little
towards the left, so that it may counterbalance the chilliness of that
side. For the left side is colder in man, as compared with the
right, than in any other animal. It has been stated in an earlier
treatise that even in fishes the heart holds the same position as in
other animals; and the reason has been given why it appears not to
do so. The apex of the heart, it is true, is in them turned towards
the head, but this in fishes is the front aspect, for it is the