52 



HAND-BOOK OF PHYSIOLOGY. 



Their action in respiration has been already referred to (p. 189, Vol. I.). 

 In the present chapter the sound produced by the vibration cf the vocal 

 cords is the only part of their function with which we have to deal. 



Anatomy of the Larynx. The principal parts entering into the for- 

 mation of the larynx (Figs. 294 and 295) are (t) the thyroid cartilage; (c) 

 the cricoid cartilage; (a) the two arytenoid cartilages; and the two true 

 vocal cords (A, cv, Fig. 298). The epiglottis (Fig. 298 e), has but little 

 to do with the voice, and is chiefly useful in falling down as a "lid" over 

 the upper part of the larynx, to help in preventing the entrance of food 

 and drink in deglutition. It also guides mucus or other fluids in small 

 amount from the mouth around the sides of the upper opening of the 

 glottis into the pharynx and oesophagus: thus preventing them from 

 entering the larynx. The false vocal cords (cvs, Fig. 298), and the ven- 

 tricle of the larynx, which is a space between the false and the true cord 

 of either side, need be here only referred to. 



Cartilages. The thyroid cartilage (Fig. 296, 1 to 4) does not form a 

 complete ring around the larynx, but only covers the front portion. The 



FIG. 296. 



FIG. 297. 



FIG. 296. Cartilages of the larynx seen from before. 1 to 4, thyroid cartilage; 1, vertical ridge 

 or pomum Adami; 2, right ala; 3, superior, and 4, inferior cornu of the right side; 5, 6, cricoid carti- 

 lage; 5, inside of the posterior part; 6, anterior narrow part of the ring; 7, arytenoid cartilages. X %. 



FIG. 297. Lateral view of exterior of the larynx. 8, thyroid cartilage; 9, cricoid cartilage; 10, 

 crico-thyroid muscle; 11, crico-thyroid ligament; 12, first rings of trachea. (Willis.) 



cricoid cartilage (Fig. 296, 5, 6), on the other hand, is a complete ring; 

 the back part of the ring being much broader than the front. On the 

 top of this broad portion of the cricoid are the arytenoid cartilages (Fig. 

 298 a) the connection between the cricoid below and arytenoid cartilages 

 above being a joint with synovial membrane and ligaments, the latter 

 permitting tolerably free motion between them. But although the 

 arytenoid cartilages can move on the cricoid, they of course accompany 

 the latter in all their movements, just as the head may nod or turn on 



