THE LAi 



FIG. 960. Muscles of the larynx, seen from above. 

 (Enlarged.) 





from the base of one cartilage to the apex of the opposite one, and therefore 

 cross each other like the limbs of the letter X; a few fibers are continued around 

 the lateral margin of the cartilage, and 

 are prolonged into the aryepiglottic fold; 

 they are sometimes described as a sepa- 

 rate muscle, the Aryepiglotticus. The 

 Arytaenoideus transversus crosses trans- 

 versely between the two cartilages. 



The Thyreoarytsenoideus ( Thyroary- 

 tenoid] (Figs. 959, 960) is a broad, thin, 

 muscle which lies parallel with and lateral 

 to the vocal fold, and supports the wall of 

 the ventricle and its appendix. It arises 

 in front from the lower half of the angle 

 of the thyroid cartilage, and from the 

 middle cricothyroid ligament. Its fibers 

 pass backward and lateralward, to be in- 

 serted into the base and anterior surface 

 of the arytenoid cartilage. The lower and 

 deeper fibers of the muscle can be differ- 

 entiated as a triangular band which is 

 inserted into the vocal process of the 

 arytenoid cartilage, and into the adjacent 

 portion of its anterior surface; it is 



termed the Vocalis, and lies parallel with the vocal ligament, to which it is ad- 

 herent. 



A considerable number of the fibers of the Thyreoarytsenoideus are prolonged 

 into the aryepiglottic fold, where some of them become lost, while others are con- 

 tinued to the margin of the epiglottis. They have received a distinctive name, 

 Thyreoepiglotticus, and are sometimes described as a separate muscle. A few fibers 

 extend along the wall of the ventricle from the lateral wall of the arytenoid cartilage 

 to the side of the epiglottis and constitute the Ventricularis muscle. 



Actions. In considering the actions of the muscles of the larynx, they may be conveniently 

 divided into two groups, vix.: 1. Those which open and close the glottis. 2. Those which regu- 

 late the degree of tension of the vocal folds. 



The Cricoarytanoidei posteriores separate the vocal folds, and, consequently, open the glottis, 

 by rotating the arytenoid cartilages outward around a vertical axis passing through the crico- 

 arytenoid joints; so that their vocal processes and the vocal folds attached to them become 

 widely separated. 



The Cricoarytcenoidei laterales close the glottis by rotating the arytenoid cartilages inward, 

 so as to approximate their vocal processes. 



The Arytaenoideus approximates the arytenoid cartilages, and thus closes the opening of 

 the glottis, especially at its back part. 



The Cricothyreoidei produce tension and elongation of the vocal folds by drawing up the arch 

 of the cricoid cartilage and tilting back the upper border of its lamina; the distance between the 

 vocal processes and the angle of the thyroid is thus increased, and the folds are consequently 

 elongated. 



The Thyreoarytcenoidei, consisting of two parts having different attachments and different 

 directions, are rather complicated as regards their action. Their main use is to draw the aryte- 

 noid cartilages forward toward the thyroid, and thus shorten and relax the vocal folds. But, 

 owing to the connection of the deeper portion with the vocal fold, this part, if acting separately, 

 is supposed to modify its elasticity and tension, while the lateral portion rotates the arytenoid 

 cartilage inward, and thus narrows the rima glottidis by bringing the two vocal folds together. 



The manner in which the entrance of the larynx is closed during deglutition is referred to 

 on page 1140. 



Mucous Membrane. The mucous membrane of the larynx is continuous above with that 

 lining the mouth and pharynx, and is prolonged through the trachea and bronchi into the lungs. 

 It lines the posterior surface and the upper part of the anterior surface of the epiglottis, to which 





