1892.] On the Mechanism of the Closure of the Larynx. 327 



If it be a simple voluntary closure of the laryngeal entrance, with 

 or without expiratory effort, that is under observation, nothing further 

 is to be noted. When the entrance is opened the arytenoids leave 

 the epiglottis and then each other, are rotated outwards and back- 

 wards, move bodily outwards, glide backwards, and thus again assume 

 the position they occupy in respiration. 



If, however, the entrance is to be closed as a part of the act of 

 swallowing, then, of course, the well known movement of the entire 

 larynx upwards and forwards ensues, and the tips of the arytenoids 

 are seen to be jammed firmly against the epiglottis. This is due 

 partly to the thyro-arytenoid vigorously rotating the arytenoids 

 inwards, and pulling them downwards and forwards, so that their 

 tips come into contact with the base of the epiglottis ; partly, how- 

 ever, it is due to the elevators of the larynx pulling the larynx 

 upwards and forwards against the base of the tongue. In this 

 position of the larynx the epiglottis lies between the rest of the larynx 

 and the tongue and is firmly applied to both, is in fact compressed 

 between them. It is, however, clear that if the epiglottis were not 

 there the laryngeal entrance would still be closed, partly by the 

 gathering up of its margins as above described, and partly by its 

 direct contact with the base of the tongue, there being now no epi- 

 glottis to intervene. 



The behaviour of the distal or apical portion of the epiglottis at 

 this stage is not the same in all animals. In the Dog, for instance, the 

 epiglottis is extremely flexible, and comparatively short, and is thus 

 easily engaged between the tongue and the larynx. In the Dog, there- 

 fore, the distal portion of the epiglottis has the appearance of closing 

 the laryngeal orifice in the lid-like way usually described as general 

 in its application ; but how little this is essential is at once evident 

 when we remember the little or no inconvenience following its com- 

 plete removal. In animals such as the Goat, which, like Man, has the 

 distal portion of the epiglottis long and stiff, quite another picture is 

 presented during this stage of the act of swallowing. It is only the 

 base of -the epiglottis which is engaged between the base of the tongue 

 and the larynx ; the distal portion does not fold down as a lid, but is 

 applied to the most posterior part of the back of the tongue, so that 

 the hollow laryngeal surface of the epiglottis continues backwards 

 the surface over which the bolus glides from the tongue. 



This, I think, may indicate the function of the hyo-epiglottic 

 muscle about which there has been so much doubt. May it not 

 serve to pull the epiglottis towards the hyoid bone during the act 

 of deglutition, so that the epiglottis would be drawn upwards 

 and forwards with the larynx ? The hyo-epiglottic muscle would 

 then stand in the same relation to the epiglottic cartilage as the 

 hyo-thyroid muscle does to the thyroid cartilage. In this way the 



