DEGLUTITION. 221 



therefore, be hardly any tendency at that time to the entrance of foreign substances into 

 the larynx. During a regular act of swallowing, nothing can find its way into the respir- 

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

 food passes through the pharynx into the oesophagus. 



The situation of the epiglottis has naturally led physiologists to attribute to it great 

 importance in preventing the entrance of particles of food and liquids into the larynx. It 

 will be remembered that this cartilaginous, leaf-like process is attached to the anterior 

 portion of the larynx, and is usually erect, lying against the base of the tongue. In the 

 movements of the tongue and larynx incident to deglutition, the epiglottis is necessarily 

 applied to the superior face of the larynx so as to close the opening. Although, during 

 deglutition, the glottis is covered in this way, it is necessary to study closely all the con- 

 ditions which are involved and to ascertain what is the actual value of each of the various 

 means by which entrance of foreign bodies into the air-passages is prevented, for this 

 protection is accomplished by several distinct provisions. 



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

 tions 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, we can imitate the natural move- 

 ments of the tongue and larynx, and it is evident that this provision alone must be suffi- 

 cient to protect the larynx from the entrance of solid or semisolid particles of food, 

 particularly when we remember how the alimentary particles are agglutinated by the 

 saliva and how easy their passage becomes over the membrane coated with a slimy 

 mucus. Experiments on the inferior animals and observations upon the human subject 

 have conclusively settled the question that the deglutition of all articles, except liquids, is 

 generally effected without difficulty when the epiglottis has been removed or lost by 

 accident or disease. The same is true when, in addition, the intrinsic muscles of the 

 larynx have been paralyzed by the section of nerves, or even when closure of the rima 

 glottidis is forcibly prevented. It has been shown, however, by the experiments of 

 Longet, that, when the larynx is in part prevented from performing its movement of 

 ascension, the deglutition of a moist mass of alimentary matter is effected with difficulty 

 and is followed by a sharp cough, indicating the entrance of a certain quantity of foreign 

 matter into the air-passages. 



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 fall together, as they always do except in inspiration. This fact we have 

 repeatedly observed in demonstrating the respiratory movements of the glottis; for, 

 when the larynx is thus exposed, the animal makes frequent efforts at deglutition. In 

 addition to this passive and incomplete approximation of the vocal chords, it has repeat- 

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

 each act of deglutition. 



Longet justly attaches great importance to the exquisite 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, on 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. 

 This is attributed to the want of sensibility in the mucous membrane above the glottis: 

 "for the animal is not aware in time of the presence of liquid which may accidentally 

 get into the supra-laryngeal cavity, the occlusion of the glottis is sometimes too tardy 

 and does not take place until after the passage of the liquid ; or, again, the animal, in- 

 stead of then making a sudden expiration, makes an unseasonable inspiration which 

 facilitates the introduction of the foreign substance into the air-passages, and the cough 



