DIGESTION. 



161 



B 



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 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. 



Because of the possibility that this 

 position of the epiglottis was due to 

 pathologic causes, Kanthack and An- 

 derson instituted a new series of ex- 

 periments 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- 

 trance of food, in the rabbit at least, by the closure of the glottis itself. This 

 experimenter noticed, while observing the interior of the larynx, both from 

 above, through an opening in the hyothyreoid membrane, and from below, 

 through an opening in the trachea, that when an act of deglutition was excited 

 by touching the soft palate with a sound, there was simultaneously with the 

 contraction of the mylohyoid muscles, a firm closure of the glottis. This 

 was accomplished by an approximation of the true vocal bands, a close 

 approximation and a downward and forward movement of the arytenoid 

 cartilages, until they almost touched the anterior wall of the thyroid carti- 

 lage. This movement preceded the ascent of the larynx. When the larynx 

 was separated from all surrounding structures with the exception of the 



Trachea* 



FIG. 70. DIAGRAM SHOWING THE MAN- 

 NER OF CLOSURE OF THE POSTERIOR NARES 

 AND LARYNX DURING DEGLUTITION. (Lan- 

 dois and Stirling.} 



