182 DIGESTION. 



nares and the Eustachian tubes, above ; and below, the open- 

 ing of the larynx. The mechanism by which these passages 

 are closed during the acts of deglutition is one of the most 

 interesting subjects connected with this function, and Jias 

 long engaged the attention of physiologists. 



The tongue a muscular organ capable of a great variety 

 of movements, and endowed, as we have seen, with highly 

 important functions connected with mastication is the chief 

 agent in the first processes of deglutition. Its physiological 

 anatomy has already been considered. 



The pharynx, in which the, most vigorous and complex 

 of the movements of deglutition take place, is an irregularly 

 funnel-shaped cavity, its longest diameter being transverse and 

 opposite the cornua of the hyoid bone, with its smallest por- 

 tion at the opening into the oesophagus. Its length is about 

 four and a half inches. It is connected superiorly and pos- 

 teriorly with the basilar process of the occipital bone and 

 the upper cervical vertebrse. It is imperfectly separated 

 from -the cavity of the mouth by the velum pendulum palati, 

 a movable musculo-membranous fold, continuous with the 

 roof of the mouth and marked by a line in the centre, which 

 indicates its original development in two lateral halves. 

 This, which is called the soft palate, when relaxed, presents 

 a concave surface looking toward the mouth, a free, arched 

 border, and a conical process hanging from the centre, called 

 the uvula. On either side of the soft palate are two curved 

 pillars or arches. 



The anterior pillars of the fauces are formed by the pala- 

 to-glossus muscle on either side, and run obliquely downward 

 and forward ; the mucous membrane which covers them be- 

 coming continuous with the membrane of the base of the 

 tongue. The posterior pillars are more closely approxi- 

 mated to each other than the anterior. They run obliquely 

 downward and backward, their mucous membrane becoming 

 continuous with the membrane covering the sides of the 

 pharynx. Between the lower portion of the anterior and 



