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.
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