DIGESTION 



163 



B 



At the moment the food passes into the pharynx the posterior nasal open- 

 ings are closed against the entrance of the food by a septum formed by the 

 pendulous veil of the palate and the posterior half arches. The palate is 

 drawn upward and backward by the levator palati muscles, until it meets 

 the posterior wall of the pharynx, which at this moment advances. At the 

 same time it is made tense, by the action of the tensor palati muscles. (Fig. 

 68.) This septum is completed by the advance toward the middle line of the 

 posterior half arches caused by the contraction of the muscles, the palato- 

 pharyngei, which compose them. When these structures are impaired in 

 their functional activity, as in diphtheritic paralysis and ulcerations, there 

 is not infrequently a regurgitation of food, especially liquids, into the nose. 



The larynx is equally protected against the entrance of food during 

 deglutition under normal circumstances. That this accident occasionally 

 happens, giving rise to severe spasmodic coughing, and even in extreme 

 cases to suffocation, is abundantly shown by the records of clinical medicine. 

 Usually it does not occur, for the following reasons: just preceding and dur- 

 ing the act of deglutition there is a complete suspension of the act of inspira- 

 tion, by which particles of food might otherwise be drawn into the larynx; 

 at the same time the larynx is always drawn well up under the base of the 

 tongue and its entrance closed by the 

 downward and backward movement 

 of the epiglottis, the result of the con- 

 traction of the aryteno-epiglottidean 

 muscle. 



The action here attributed to the 

 epiglottis has been denied by Stuart 

 and McCormick. These observers 

 had the opportunity of looking into 

 a naso-pharynx which had been laid 

 open by a surgical operation for the. 

 removal of a morbid growth. In this 

 patient, the epiglottis, at the time of 

 deglutition, was always more or less 

 erect and closely applied to the base 

 of the tongue. So complete was this 

 that the food passed over its posterior 

 or inferior surface for a certain dis- 

 tance. In no instance was it ever ob- 

 served to fold backward like a lid. FlG - 68. DIAGRAM SHOWING THE MAN- 



T, e .-, MM-- ,-L L J.T-* N ER OF CLOSURE OF THE POSTERIOR NARES 



Because of the possibility that this AND LARYNX DURING DEGLUTITION.- (Lan- 



position of the epiglottis was due to dois and Stirling.} 



pathologic causes, Kanthack and An- 

 derson instituted a new series of experiments with a view of determining 

 the action of the epiglottis. As a result of many experiments on animals 

 and of observations on themselves, these observers reaffirm the gener- 

 ally accepted view, that under normal conditions, the entrance of the larynx 

 is always closed by the epiglottis after the manner of a lid. 



In addition to the downward and backward movement of the epiglottis 

 and the ascent of the larynx under the base of the tongue, it is also certain 

 from the observations of Meltzer that the larynx is protected from the en- 



Trachea* 



