318 



THE VOICE. 



[BOOK in. 



cartilage run transversely across to the outer edge of the other 

 cartilage, and the belly of the muscle occupies the concave hind 

 surfaces of the two cartilages together with the intervening space. 



pm... 



.m.cr.ar.p 



---m. cr. ar. p 



m.cr. th.p 



FIG. 187. DIAGRAM OF THE TRANSVERSE AND OBLIQUE ARYTENOID AND OF 

 THE POSTERIOR CRICO-ARYTENOID MUSCLES. 



A. shews the three muscles in position in reference to the aperture of the larynx ; 

 B. shews the attachments of the transverse arytenoid and posterior crico- 

 arytenoid. N 



m. ar. t. transverse arytenoid muscle. m. cri. ar. p. posterior crico-arytenoid 



muscle, m. ar. o oblique arytenoid muscle. Cri. Cricoid cartilage. Art/. 



Arytenoid cartilage, p m. processus muscularis of arytenoid cartilage. W. 



prominence of cartilage of Wrisberg. S. prominence of cartilage of Santorini 



(in^, it marks the cartilage itself), m cr.th.p. is the small posterior crico- 

 thyroid muscle. 



The effect of the contraction of this muscle is to bring the 

 two cartilages closer together and so to narrow the glottis ; 

 indeed if in an animal it be divided, the glottis remains widely 

 open behind. It is an important closer of the glottis, adductor of 

 the vocal cords. When it is not contracting the cartilages come 

 apart through the elastic reaction of their connections. 



Most important is a mass of muscular fibres, which starting 

 from the lower part of the re-entering angle of the thyroid pass 

 horizontally but inclined somewhat upwards to the arytenoids at 

 about the level of the vocal cords. The whole mass is described 

 as forming two muscles. The outer or lateral part ending in the 

 outer edge of the arytenoid and upper part of its processus mus- 

 cularis is called the external thyro-arytenoid (M. thyro-arytenoideus 



