VOICE AND SPEECH 



495 



wards and backwards to the muscular process. The posterior 

 crico-arytenoids, working alone, pull inwards and downwards the 

 muscular processes, turn upwards and outwards the vocal proc- 

 esses, and separate the posterior ends of the vocal cords. The 

 lateral cricothyroid, working alone, pulls downwards and for- 

 wards the muscular process, and rotates inwards and upwards 

 the vocal process, and narrows the glottis; it is the chief agent in 

 producing the approximation of the cords necessary for the pro- 

 duction of voice. When both pairs of muscles act together, how- 

 ever, each neutralizes the tendency of the other to rotate the 



aep 



FIG. 147. The larynx seen from behind and dissected so as to display some of 

 its muscles. The mucous membrane of the front of the pharynx (5, Fig. 146) has 

 been dissected away, so as to display the laryngeal muscles beneath it. Part of 

 the left half of the thyroid cartilage has been cut away, co, cartilage of San- 

 torini ; cu, cartilage of Wrisberg. 



arytenoid cartilage ; the downward part of the pull of each is, thus, 

 alone left, and this causes the arytenoid to slip downwards and 

 outwards, off the eminence on the cricoid with which it articu- 

 lates, as far as the loose capsular ligament of the joint will allow. 

 The arytenoid cartilages are thus moved apart and the glottis 

 greatly widened and brought into its state in deep quiet breathing. 



