Erasistratus denies that the stomach exerts any pull in
the act of swallowing. That he is wrong, however, is
proved by the anatomical structure of the stomach--its
inner coat with longitudinal fibres obviously acts as a
_vis a fronte_ (attraction), whilst its outer coat
exercises through the contraction of its circular fibres
a _vis a tergo_ (propulsion); the latter also comes into
play in vomiting. The stomach uses the oesophagus as a
kind of hand, to draw in its food with. The functions of
the two coats proved also by vivisection. Swallowing
cannot be attributed merely to the force of gravity.