VOICE AND SPEECB. 637 



ordinated activity of a number of small muscles, which move 

 the cartilages to which the cords are fixed. 



The Muscles of the Larynx. In describing the direc- 

 tion and action of these it is convenient to use the words 

 front or anterior and back or posterior with reference to the 

 larynx itself (that is, as equivalant to ventral and dorsal) and 

 not with reference to the head, as usual. The base of each 

 arytenoid cartilage is triangular and fits on a surface of the 

 cricoid, on which it can slip to and fro to some extent, the 

 ligaments of the joint being lax. One corner of the tri- 

 angular base is directed inwards and forwards (i.e. towards 

 the thyroid) and is called the vocal process (Pv, Fig. 181), as 

 to it the vocal cords are fixed. The outer posterior angle 

 (Pm, Fig, 181) has several muscles inserted on it and is 

 called the muscular process. If it be pulled back and 

 towards the middle line the arytenoid cartilage will rotate on 

 its vertical axis, and roll its vocal processes forwards and out- 

 wards, and so widen the glottis; the reverse will happen if 

 the muscular process be drawn forwards. The muscle pro- 

 ducing the former movement is the posterior crico-arytenoid 

 (Cap, Fig. 183); it arises from the back of the cricoid carti- 

 lage, and narrows to its insertion into the muscular process 

 of the arytenoid on the same side. The opponent of this 

 muscle is the lateral crico-arytenoid, which arises from the 

 side of the cricoid cartilage, on its inner surface, and passes 

 upwards and backwards to the muscular process. The pos- 

 terior crico-arytenoid s, working alone, pull inwards and down- 

 wards the muscular processes, turn upwards and outwards 

 the vocal processes, and separate the posterior ends of the 

 vocal cords. The lateral crico-thyroid, working alone, pulls 

 downwards and forwards 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 production of voice. When 

 both pairs of muscles act together, however, each neutralizes 

 the tendency of the other to rotate the 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 articulates, 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 



