182 DIGESTION 



diaphragm between the postero-superior and the antero-inferior .parts of 

 the pharynx. This, with the application of the posterior wall of the 

 pharynx to the superior face of the soft palate, completes the protection 

 of the posterior openings of the nasal fossae. 



Protection of the Opening of the Larynx and Uses of the Epiglottis in 

 Deglutition. The entrance of the smallest quantity of solid or liquid 

 foreign matter into the larynx produces a violent cough. This accident 

 is of not infrequent occurrence, especially when an act of inspiration 

 is inadvertently performed while solids or liquids are in the pharynx. 

 During inspiration, the glottis is opened, and at this time only can a 

 substance of any considerable size find its way into the respiratory pas- 

 sages. Respiration is interrupted, however, during each and every act 

 of deglutition ; and there can, therefore, be hardly any tendency at this 

 time to the entrance of foreign substances into the larynx. During a 

 regular act of swallowing, nothing can find its way into the respiratory 

 passages, so complete is the protection of the larynx during the period 

 when the food passes through the pharynx into the oesophagus. 



It is evident, from the anatomy of the parts and the necessary results 

 of the contractions of the muscles of deglutition, that while the food is 

 passing through the pharynx, the larynx, by its elevation, passes under 

 the tongue as it moves backward, and the soft base of this organ is, as 

 it were, moulded over the glottis. With the parts removed from the 

 human subject or from one of the inferior animals, the natural move- 

 ments of the tongue and larynx may be roughly imitated, and it is seen 

 that they must be sufficient to protect the larynx from the entrance of 

 solid or semisolid particles of food. It is impossible for the muscles 

 of the pharynx to contract without drawing together the sides of the 

 larynx, to which they are attached, and assisting to close the glottis. 

 At the same time, as the movements of respiration are arrested during 

 deglutition, the lips of the glottis are more nearly approximated. In 

 addition to this passive and incomplete approximation of the vocal 

 chords, it has been observed that the lips of the glottis are accurately 

 and firmly closed, during each act of deglutition, by contraction of the 

 adductor muscles. 



Importance is justly attached to the acute sensibility of the top of 

 the larynx in preventing the entrance of foreign substances. The 

 experiments of dividing all the nervous filaments distributed to the 

 intrinsic muscles show that their action is not essential ; but after 

 division of the superior laryngeal the nerve which gives sensibility 

 to the parts it has been found that liquids occasionally pass in 

 small quantity into the trachea. 



With reference to the action of the epiglottis in contributing to the 



