INTRINSIC MUSCLES OF THE LARYNX. 489 



with parallel sides (A'), while the cords are made more or less 

 tense, according to the pitch of the note to be produced ; both 

 these changes being brought about by muscular action. 



The opening of the chink of the glottis is accomplished chiefly 

 by a muscle called the posterior crico-arytenoid, which passes 

 from the posterior surface of the cricoid cartilage to the outer and 

 posterior angle of the arytenoids. By pulling the latter point 

 downward and backward it separates the arytenoid cartilages, 

 particularly at their anterior extremity, where the cords are 

 attached. In this action they are aided by a small muscle con- 

 necting the posterior surfaces of the arytenoid, namely, the 

 posterior arytenoid, which tends, when the two arytenoid carti- 

 lages are held apart, to rotate them so that the vocal processes 

 are separated. 



The narrowing of the glottis is executed by the lateral crico- 

 arytenoids which run upward and backward from the antero- 

 lateral aspect of the cricoid to the muscular process of the ary- 

 tenoid cartilages. They pull the muscular processes forward, 

 and thus rotate the arytenoid cartilages so as to approximate the 

 vocal processes to one another, while any tendency toward pull- 

 ing apart the bodies of the cartilages, owing to the downward 

 direction of the muscle, is overcome by the posterior arytenoid 

 muscle and those muscular bands which pass from the posterior 

 surface of the arytenoid cartilages to the epiglottis and the upper 

 part of the thyroid cartilage, the external thyro-arytenoid, and 

 the thyro-aryepiglottic muscles (Henle). The other fibres, 

 which pass directly from the arytenoid to the thyroid cartilages 

 internal and external thyro-arytenoid muscles in the same 

 direction as the vocal cords, complete the closure by helping to 

 press together the vocal processes and by approximating the 

 cords themselves. In spasmodic closure of the glottis, all these 

 latter muscles act violently together, and have been grouped by 

 Henle as the constrictor of the glottis. Relaxation of the vocal 

 cords accompanies voluntary closure of the glottis, as in holding 

 the breath, when the false vocal cords are said to have a valvular 

 action. But the muscular fibres, which run from the arytenoid 

 cartilages to the thyroid, nearly parallel to the true vocal cords, 



