1892.] On the Mechanism of the Closure of the Larynx. 337 



arytenoid ridge contains the antero-posterior limb of the "]~- nsSTire i 

 but it is much shorter and less prominent than in the Kangaroo. 



The elastic nature of the tips of the arytenoids and the Santorinian 

 cartilages admirably fits them for gliding into position down the 

 front of the laryngeal cavity. In this respect also, the form of the 

 Santorinian cartilages, convex forwards in the closed aperture, helps, 

 and the cushion of the epiglottis, when present, corresponds to the 

 interval between them. In the open aperture, the tips of the corni- 

 cula are directed inwards and backwards, but this merely brings them 

 parallel when the arytenoids are in the closed position. The elastic 

 nature of all these cartilages enables them to fit each other perfectly 

 when brought into apposition, and to recover their shape when the 

 pressure is removed, and the pad of fat in front of the epiglottis helps 

 in this connexion. Even in the dead subject, these phenomena can be 

 observed more or less by simply pressing the arytenoids forwards 

 the closure is perfect without the epiglottis ever moving. 



In animals with the cornicula more highly developed than they 

 are in Man and the Goat, this account does not apply. In the Dog, 

 for instance, they are long and pointed, and are pushed aside out of 

 the mesial plane when the larynx is closed. 



The superior or false vocal cords, as the arytenoids are rotated 

 inwards, of course, come into apposition with each other, since 

 posteriorly they are attached to the anterior margins of the arytenoids 

 and anteriorly they are attached together to the re-entrant angle of 

 the thyroid cartilage. As the arytenoid cartilages move forwards, 

 the superior cords are shortened from before backwards, and possibly 

 this may account for the large amount of elastic tissue in their struc- 

 ture, and it may possibly be the office of the bundles of striped 

 muscular fibres, which have been described as radiating into the false 

 cords from various muscles of the region, to perform a similar func- 

 tion, that of taking up the slack of the shortened false cord. As the 

 action of the thyro-arytenoid is continued, the soft substance of these 

 cords will tend to be squeezed both upwards into contact with the 

 advancing arytenoids, and downwards to encroach on the ventricle. 

 At the same time, the sacculi will be compressed from the sides by 

 the thyro-arytenoids and from behind by the arytenoid cartilages. 

 This may be the reason why the sacculus is over only the anterior 

 part of the ventricle, for here it is out of the way of the advancing 

 arytenoid, and any secretion which might be squeezed out of it 

 would immediately pervade the whole length of the ventricle, now 

 narrowed by the encroachment of the false cords, and so would lubri- 

 cate the whole length of the true cord, although the sacculus is over 

 the anterior part only. The fact that we often swallow when the 

 cords are dry, as in hoarseness after much speaking, supports this 

 idea, for the saliva swallowed cannot possibly affect the cords ; the 



