CHAP, vii.] SPECIAL MUSCULAR MECHANISMS. 1075 



may speak of these two actions as narrowing or widening of the 

 glottis, adduction or abduction of the edges of the glottis, and 

 tightening or relaxation of the vocal cords. We may first dwell 

 on the muscular aspects of the mechanisms by which these results 

 are brought about, taking the nervous factors into consideration 

 afterwards. The change of form of the glottis is best understood 

 when it is borne in mind that each arytenoid cartilage is, when 

 seen in horizontal section (Fig. 187), somewhat of the form of 

 a triangle, with a median, an external, and a posterior side, the 

 processus vocalis being placed in the anterior angle at the junc- 

 tion of the median and external sides. When the cartilages are 

 so placed that the processus vocales are approximated to each 

 other and the internal surfaces of the cartilages nearly parallel, 



FIG. 187. THE LARYNX AS SEEN BY MEANS OF THE LARYNGOSCOPE IN DIFFERENT 

 CONDITIONS OF THE GLOTTIS. (From Quain's Anatomy, after Czermak.) 



A while singing a high note ; B in quiet breathing ; C during a deep inspira- 

 tion. The corresponding diagrammatic figures A', J5', C", illustrate the changes 

 in position of the arytenoid cartilages, and the form of the rima vocalis and 

 rima respiratoria in the above three conditions. 



I the base of the tongue ; e the upper free part of the epiglottis ; e' the 

 tubercle or cushion of the epiglottis ; ph. part of the anterior wall of the pharynx 

 behind the larynx ; w swelling in the aryteno-epiglottidean fold caused by the 

 cartilage of Wrisberg ; s swelling caused by the cartilage of Santorini ; a the 

 summit of the arytenoid cartilage ; cv the vocal cords ; cvs the ventricular bands ; 

 tr the trachea with its rings ; 6 the two bronchi at their commencement. 



