292 



THE LAETNX. 



their fibres ai'e partly attaclicd to the upper and outer part of the 

 opposite cartilage, partly pass forwards in the aryteno-epiglottidean fold, 

 and partly join the fibres of the thyro-arytenoid muscle. 



A few fibres associated with the anterior and upper part of the 

 thyro-arytenoid muscle have been described as a tlnjro-epiijloltidecm 

 muscle. 



Actions of the intrinsic muscles of the larynx.— The crlco-ilii/roid muscles 

 ■pi-odiTce the rotation forwards and downwards of the thyroid cartilage on the 

 cricoid, which is permitted by the crico-thyrbid' articulations (fig. 11)7). In this 



c«p 



Fig. 197. — Outline of the TaGHT Half 

 OP THE Cartilages of the Larynx as 



SEEN FROM THE InSIDE, WITH THE THYRO- 

 ARYTENOID Ligament, to illustrate 

 THE Action op the Crico-Thtroid 

 Muscle (Allen Thomson). 



t, cut surface of the thyroid cartilage in 

 the middle anteriorly ; c, c, the same of the 

 cricoid cartilage before and behind ; a, the 

 inner surface of the right arytenoid carti 

 lage ; a', its anterior process ; «, the right 

 cartilage of Sautorini ; c v, the thyro-ai'y- 

 tenoid ligament ; the position of the lower 

 cornu of the thyroid cartilage on the out- 

 side of the cricoid is indicated by a dotted 

 outline, and r indicates the point or axis 

 of rotation of the one cartilage on the other ; 

 c t h, indicates a line in the principal direc- 

 tion of action of the crico-thyroid muscle ; 

 c a p, the same of the posterior crico- 

 arytenoid muscle ; the dotted line, of which 

 i' indicates a part, represents the position 

 into which the thyroid cartilage is moved 

 by the action of the crico-thyroid muscle ; 

 if the arytenoid cartilages are fixed by 

 muscles acting in the direction of c a j5, 

 the vocal cords will be elongated and 

 rendered tense by contraction of the crico- 

 thyroid muscles, as indicated by c v". 



■movement the arytenoid cai-tilages. being attached to the ci-icoid cartilage at a 

 level considerably above the axis of rotation, have their distance from the fore- 

 part of the thyroid cartilage increased, and, in this way. the crico-thjToid muscles 

 increase the tension of the vocal cords. The f/ii/ro-ari/tnioul muscles are. in 

 their lower parts, the opponents of the crico-thjToid. raising the fore part of the 

 thyroid cartilage and decreasing the tension of the vocal cords; the upper parts 

 "of these muscles, he'mg attached higher up on the arj-tenoid cartilages, depress 

 them. 



The lateral fviro-ari/fetwid muscles, by pulling forwards the outer angles of 

 the arytenoid cartilages, approximate the vocal cords to the middle line. The 

 ptntcrim- criro-arijtcHokl muscles pull backwards the outer angles of the arytenoid 

 cartilages, and thus draw asunder the posterior extremities of the vocal cords, 

 and dilate the glottis to its greatest extent : they are likewise the elevators of 

 the arytenoid cartilages. 



The avjjtrnoid muscle di-aws the arytenoid cartilages together, and, from the 

 (•■tructure of the crico-arytenoid joints, this approximation -when complete is 

 necessarily accompanied with depression. Tlie ariitnw-rp'mloiiUlran muscles at 

 once depress and approximate the arytenoid cartUages, which they include in 

 their embrace, and draw down the epiglottis, so as to contract the whole superior 

 apcrtui-e of the larjaix 



