208 DIGESTION MASTICATION, INSALIVATION, DEGLUTITION. 



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 inadvert- 

 entty performed while solids or liquids are in the pharynx. During inspi- 

 ration, the glottis is opened, and at that time only can a substance of any 

 considerable size find its way into the respiratory passages. Respiration is in- 

 terrupted, however, during each and every act of deglutition ; and there can, 

 therefore, be hardly any tendency at that time to the entrance of foreign sub- 

 stances 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 movements of the tongue and larynx 

 can be imitated, and it is seen that they must be sufficient to protect the 

 larynx from the entrance of solid or semi-solid particles of food, particu- 

 larly when it is remembered how the alimentary particles are agglutinated 

 by the saliva and how easy their passage becomes over the membrane coated 

 with mucus. It is impossible, also, for the muscles of the pharynx to con- 

 tract 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 move- 

 ments of respiration are arrested during deglutition, the lips of the glottis 

 fall together, as they always do except in inspiration. In addition to this 

 passive and incomplete approximation of the vocal chords, it has repeatedly 

 been observed that the lips of the glottis are accurately and firmly closed 

 during each act of deglutition. 



Longet justly attached great importance to the acute sensibility of the 

 top of the larynx in preventing the entrance of foreign substances. His 

 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 he found 

 that liquids occasionally passed in small quantity into the trachea. 



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

 tection of the larynx during the second period of deglutition, observations on 

 the human subject only are to be relied upon. Such observations, in cases of 

 loss of the epiglottis especially, show that this part is necessary to the com- 

 plete protection of the larynx. While loss of the epiglottis may not inter- 

 fere always with the perfect deglutition of solids, and even of liquids, parti- 

 cles of food and liquids frequently find their way into the larynx, and 

 deglutition is often effected with difficulty, showing that complete protection 

 of the larynx at all times, does not exist unless the epiglottis be intact. 



To appreciate the mechanism by which the opening of the larynx is pro- 



