1892.] On the Mechanism of the Closure of the Larynx. 333 



anterior margins of the arytenoid cartilages, and tlms brings together 

 the sides of the vestibule, and then it inclines the arytenoids so as to 

 encroach on the space from above downwards, and from behind for- 

 wards the three muscles, that is, the two thyro-arytenoids and the 

 transverse arytenoid, now grasp the vestibule, so to speak, obliterate 

 its space, and thus close the larynx. With them act the ary-epiglottici 

 so as to close the very entrance. 



In certain animals there is no elastic tissue in what would corre- 

 spond to the true cord (Bland Sutton, 'Journal of Anatomy and 

 Physiology,' " Nature of Ligaments "), which thus is entirely of 

 muscle enclosed in mucous membrane. This seems to indicate the 

 primary importance of the muscle as a muscle rather than as a 

 vibrating cord, a view also expressed by Bland Sutton upon purely 

 anatomical grounds. May it not be simply that the elastic property 

 is secured for the vibrating tissue at a physiologically cheaper rate 

 through fibrous than through muscular tissue ? 



Nothing is said here of the feeble thyro-arytcenoideus internus : 

 this, probably, is the proper muscle of the vocal cords, and in any 

 case, from its feeble development and its attachments, it cannot have 

 much influence in closing the larynx. 



This description of the mode of closure of the larynx meets the 

 case during both inspiration and expiration. In closure during 

 inspiration the closure is absolute and, after the muscles have once 

 brought the parts into position, is entirely mechanical. This one can 

 easily verify by sucking air down through either the dead or the 

 living larynx. The margins of the aperture come together and 

 remain pressed together by atmospheric pressure. Against ex- 

 piration the resistance is entirely muscular, for the margins of the 

 aperture open outwards, and air can always be blown upwards so as 

 to force open the closed larynx. The thyro-arytenoid and transverse 

 arytenoid appear to me to be quite adequately developed to resist 

 pressure to a high degree, because, in the first place, these muscles 

 are really not so small as one is accustomed to think they are ; and, 

 in the second place, the surface which has to bear pressure in the 

 closed larynx is not extensive. 



In such larynges as the Lizard's, the muscle simply rotates the 

 cartilage to close the lozenge-shaped aperture which corresponds to 

 the glottis of Man. 



The Arytenoid Muscle. This muscle must be divided into (1) the 

 two oblique portions, which are really continuations of the ary- 

 epiglottic muscle, and are dealt with under that heading; and (2) 

 the transverse portion. The transverse portion alone is now under 

 consideration. Owing to the articular surface of the arytenoid car- 

 straighten themselves, and so bring the side walls of the entrance together. This, 

 of course, is quite a different thing from my account. 



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