On The Parts Of Animals   

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