338 Prof. T. P. Anderson Stuart. [Jan. 21, 



act of swallowing, however, could, by expressing the saccular secre- 

 tion, and distributing this secretion as well as the copious secretion 

 of the rest of this region over the true cords. 



The Crico-arytenoid Joint. The relatively great antero-posterior 

 diameter, the ovoid form, and plane surface of the arytenoid articular 

 surface, in the light of this description of the mode of closure of the 

 glottis are quite comprehensible. 



As the vocal process of the arytenoid with its attached true vocal 

 cord sinks into the larynx, it moves nearly in a circle, of which the 

 cord is the radius, and the cartilage glides forwards on the cricoid, 

 so that the cord's tension remains fairly equable. As a matter of fact^ 

 however, the tension of the cord in the sunk position is greater than 

 before, so that the mere gliding of the arytenoid does not wholly 

 compensate : the tilting forward of the whole cartilage is relatively 

 great, so that the vocal process is carried relatively far backwards 

 and so the cord is put upon the stretch. 



When the larynx is open the narrow end of the ovoid rests on the 

 cricoid, but in the closed larynx it is the broad end of the ovoid. In 

 the open larynx, stability is not of moment ; rather is mobility im- 

 portant, for there is no pressure to be resisted and in swallowing it is 

 of importance to get the cartilages quickly into position, and, more- 

 over, we saw that the arytenoids are in continual movement even in 

 tranquil respiration. In the closed larynx, on the other hand, 

 stability is of the utmost moment, and then, not only is the broad end 

 of the ovoid on the cricoid, but possibly the little intra-articular 

 p fibro-cartilage attached to the capsular ligament of the articulation, 

 and projecting into the joint cavity from the posterior blunt circum- 

 ference of the arytenoid articular surface (Luschka), comes into play 

 to increase the surface upon which the arytenoid rests : only along 

 a line can there be contact of the cricoid cylinder with the arytenoid 

 plane, but the fibro-cartilage probably increases this surface of con- 

 tact so that the arytenoid rests on the cricoid in front, and on the 

 intra-articular cartilage behind. The fibro-cartilage filling up the 

 angle of the joint posteriorly would play also the part of a sort of 

 patella protecting this extremely important joint from any mechanical 

 violence from the passing bolus. 



A further advantage of the gliding forwards of the arytenoid is 

 that, while in the open larynx the muscular process projects somewhat 

 behind the plane of the cricoid lamina, in the closed larynx it does 

 not, so that there is no impediment to the descending bolus, and less 

 chance of damage to the cartilage and joint. 



The long axis of the arytenoid articular surface is from behind in- 

 wards and forwards, and this is the direction in which the base 

 glides. 



The arytenoid cartilages of course glide laterally also, for the 





