VOICE AND SPEECH 



579 



in Shape. By their bases they articulate at some distance from the 

 middle line with convex articular surfaces situated in the upper margin 

 of the plate of the cricoid cartilage. The anterior angle of the base is 

 the vocal process, while the external angle is the muscular process 

 of the arytenoid. The crico-arytenoid 

 joints permit of two kinds of move- 

 ments of the arytenoid cartilages, viz. : 



(1) Kotation on their base around 

 their vertical long axis ; so that the 

 anterior vocal process is rotated out- 

 wards and the muscular process back- 

 wards and inwards or conversely. 



(2) Sliding movements of the whole 

 arytenoid cartilage either outwards or 

 inwards, so that their inner margins 

 may be drawn apart or approximated. 



The larynx is covered internally by 

 a mucous membrane continuous with 

 that of the trachea. It is lined with 

 ciliated epithelium, except over the 

 vocal cords, where the epithelium is 

 stratified. The two vocal cords, or 

 thyro- arytenoid ligaments, consist of 

 elastic fibres which run from the middle 

 of the inner angle of the thyroid carti- 

 lage to be inserted into the anterior 

 angle of the arytenoid cartilages. Their 

 length in man is about 15 mm., in 

 woman about 11 mm. The cleft be- 

 tween them is known as the glottis, or 

 rima glottidis. 



Two ridges of mucous membrane 

 above and parallel to the vocal 

 cords are the false vocal cords (Fig. 251). Between the true and 

 the false vocal cords on each side is a recess known as the ven- 

 tricle of Morgagni. This ventricle permits the free vibration of 

 the vocal cords. The false cords take no part in phonation, but 

 help to keep the true cords moistened by the secretion of the 

 numerous mucous glands with which they are provided. The posi- 

 tion and tension of the vocal cords is determined by the action of the 

 various intrinsic muscles of the larynx. The part taken by the various 

 muscles in each movement cannot be directly ascertained. We can 

 in most cases only study the direction of the fibres, and judge, from 

 this direction and consequent isolated action of the muscles, the part 



FIG. 251. Anterior half of the 

 larynx, seen from behind. The 

 section on the right side is 

 somewhat in front of the left 

 side. 



e, epiglottis ; e', cushion of 

 epiglottis ; t, thyroid cartilage ; 

 s, s', ventricle of larynx ; h, great 

 cornu of hyoid bone ; t a, thyro- 

 arytenoid muscle ; v I, vocal 

 cords. Above the ventricles are 

 the false vocal cords, r, first ring 

 of trachea. (A. THOMSON.) 



