SWALLOWING, THE ACT OF, is accomplished by a set of associated movements which have been divided by physiologists into three stages. In the first stage, the food having been previously duly reduced to a pulp by trituration and insalivation, is carried back by the contraction of various muscles until it has passed the anterior palatine arch. See PALATE. So far, the movements are purely voluntary. The second stage now com mences, during which the entrance of food into the nasal cavities and larynx is most carefully guarded against by certain reflex (involuntary) actions, which have been only clearly recognized since the introduction of the use of the laryngoscope during the last few years. The tongue is carried further backward, the larynx rises so as to be covered by the epiglottis, which is depressed and lies horizontally, so that its upper border touches the posterior wall of the pharynx. Coincident with these movements, the sides of the posterior palatine arch contract by muscular action, and approach each other like a pair of curtains, so as almost to close the passages from the fauces into the posterior nostrils; the closure being completed by the uvula. A sort of inclined plane is thus formed, and
the morsel slips downward and backward into the pharynx, which is raised to receive it. • Very little, if any, voluntary action is here exerted. The third stage—the propul sion of the food down the cesophagus—then commences, and this process is effected in the upper part by means of the constrictor muscles of the pharynx, and in the lower, by the muscular coat of the oesophagus itself. At the point where the latter enters the stomach, there is a sort of a sphincter muscle which is usually closed, but which opens when suffi cient pressure is made on it by accumulated food, closing again when this has passed. See Carpenter's Principles of Human, Physiology.