1892.] On the Mechanism of the Closure of the Larynx. 33$ 



cricoid articular surface is about half as long again as the arytenoid 

 is broad in the open larynx the arytenoids rest on the outer end of 

 the cricoid surface, in the closed larynx on the inner end, so that 

 they now lie closely apposed. Thus the action of the three true 

 sphincter or constrictor muscles brings the arytenoids exactly into 

 the position described in the closed larynx ; the thyro-arytenoidei 

 rotate the arytenoid cartilages inwards and pull them forwards, the 

 arytenoideus transversus pulls them together. The narrowing of the 

 lamina of the cricoid as we ascend has an important influence in per- 

 mitting the arytenoids to approach each other bodily, though a trian- 

 gular space, the base of which corresponds to the width of the cricoid 

 lamina, must always remain filled by the arytenoideus. 



The epithelium on the inner faces of the arytenoid cartilages is 

 stratified squamous (Davis, quoted by Klein), and this is accounted 

 for by the pressure between the two comparatively hard and resistant 

 arytenoids. Covering the greater part of the side walls of the vesti- 

 bule it is ciliated columnar, but there being no rubbing of surface 

 upon surface, the mucosa being soft, and the surface being covered 

 by a thick layer of mucus, the cilia are not damaged by the compres- 

 sion of the vestibule in deglutition. The epithelium for a little way 

 within the margin is stratified squamous ; here, however, one can 

 imagine that some friction takes place during the movements of the 

 parts. 



The shape of the epiglottis fits in with my account of the act of 

 deglutition : it lies on the posterior part of the dorsum of the tongue, 

 but it would certainly not fit the top of the larynx did it fold over 

 it as in the current description, for there is no relation either in 

 size or form, nor is there any pattern on its laryngeal surface as if 

 it were often applied to the laryngeal aperture. And, as Howes 

 writes (' Jl. Anat, Physiol.,' 1889, p. 271), " In many Quadrupedal 

 Mammals the parts are so arranged that the posterior border of the 

 velum appears to overlie the epiglottis, abutting against the ventral 

 laryngeal wall. In such a case, did the epiglottis merely function, 

 during deglutition, as a lid, the effects of its displacement would be 

 simply that of forcing it back upon the velum palati. A flapping 

 action in deglutition, as ordinarily understood, could manifestly 

 only be possible in forms in which the velum stops short of the 

 epiglottis." 



