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.
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