MUSCLES OF THE LARYNX. 



917 



attached to the upper part of the arytenoid cartilage. This is named by Scemmerring 

 the small thyro-arytenoid, whilst the two other portions of the muscle constitute the 

 great thyro-arytenoid of that author. 



Arytenoid and aryteno-epiglotlidean muscles. When the mucous mem- 

 brane is removed from the back of the arytenoid cartilages, a thick band of 

 transverse fibres constituting the arytenoid muscle is laid bare, and on the 

 surface of this are seen two slender decussating oblique bundles, formerly 

 described as portions of the arytenoid muscle (arytsenoideus obliquus), but 

 now more generally considered as parts of the aryteuo-epiglottidean muscles, 

 with which they are more closely associated both in the disposition of their 

 fibres and in their action. The arytenoid muscle passes straight across, and iU 

 fibres are attached to the whole extent of the concave surface on the back of 

 each aryteuoid cartilage. The aryteno-epiglottidean muscles arising near the 

 inferior and outer angles of the arytenoid cartilages, decussate one with the 

 other, and their fibres are partly attached to the upper and outer part of the 

 opposite cartilage, partly pass forwards in the aryteno-epiglottideau 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 constituting a thyro-epiylottidean 

 muscle. 



Fig. 643. 



Fig. 643. OUTLINE OF THE RIGHT HALF 

 OF THE CARTILAGES OP THE LARYNX AS 



SKEN FROM THE INSIDE, WITH THE THYRO- 

 ARYTENOID LIGAMENT, TO ILLUSTRATE 

 THE ACTION OF THE CRICO-THYROID 

 MUSCLE., 



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 ; s, the right 

 cartilage of Santorini ; c v, the thyro-ary- 

 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 ; 

 cth, indicates a line in the principal direc- 

 tion of action of the crico-thyroid muscle; 

 cap, the same of the posterior crico- 

 arytenoid muscle ; the dotted line, of which 

 t' indicates a part, represents the position 

 into which the thyroid cartilage is moved 

 by tlie action of the crico-tbyroid muscle ; 

 if the arytenoid cartilages are fixed by 

 muscles acting in the direction of cap, 

 the vocal ligaments will be elongated and 

 rendered tense by contraction of the crico- 

 thyroid muscles, as indicated by cv'. 



Actions of the intrinsic muscles of the larynx. The crico-thyroid muscles produce 

 the rotation forwards and downwards of the thyroid cartilage on the cricoid, which is 

 permitted by the crico-thyroid articulations. In this movement the arytenoid carti- 

 lages, being attached to the cricoid cartilage at a level considerably above the axis of 

 rotation, have their distance from the fore part of the thyroid cartilage increased, and 

 therefore, the crico-thyroid muscles increase the tension of the vocal cords. The 

 thyro-arytenoid muscles are, in their lower parts, the opponents of the crico-thyroid, 

 raising the fore part of the thyroid cartilage and decreasing the tension of the vocal 



cth/ 



