PART IV 

 VOICE AND SPEECH 



THE development of the analytical powers of the auditory apparatus 

 is so closely connected with that of the faculty of speech that we may 

 conveniently deal with the latter at this point rather than relegate it to 

 a chapter on special muscular mechanisms. We may first consider the 

 mechanism of production of voice, which man shares with many other 

 animals, before discussing the mechanism of the wholly human faculty 

 of speech. 



Voice is produced in the larynx, a modified portion of the wind-pipe, 

 by the vibrations of two elastic bands, the vocal cords, which are set into 

 action by an expiratory current of air from the lungs. In many respects 

 the larynx resembles a reed instrument, in which a current of air is caused to 

 vibrate by the vibrations of an elastic tongue. Whereas however the period 

 of the vibrations in such an instrument, and therefore the note, is deter- 

 mined by the length of the tube which is attached to the reed and by the 

 lengths of the reeds themselves, in the larynx the note produced by the blast 

 of air is modified partly by alterations in the tension of the vocal cord, and 

 partly by varying the strength of the blast of air. 



ANATOMICAL MECHANISM OF THE LARYNX. The essential framework 

 of the larynx is formed by four cartilages, viz. the cricoid, the thyroid, and the two 

 arytenoid cartilages. The cricoid cartilage, which lies immediately over the upper- 

 most ring of the trachea, is shaped like a signet ring, the small narrow part being 

 directed forwards and the broad plate backwards. The thyroid cartilage consists of 

 two parts or alse, joined together in front and forming the prominence known as Adam's 

 apple ; behind, it presents four processes or cornua, the superior of which are attached 

 by ligaments to the hyoid bone, while the inferior cornua articulate with the postero- 

 lateral portion of the cricoid cartilage. By means of this articulation very free move- 

 ment is permitted between the two cartilages, the general direction of movement being 

 one of rotation of the cricoid cartilage on the thyroid, round a horizontal axis directly 

 through the two articular surfaces between the two cartilages, while movements of the 

 thyroid upon the cricoid are also possible in the upward, downward, forward, and back- 

 ward directions. The two arytenoid cartilages are pyramidal 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 movements of the 

 arytenoid cartilages, vix. : 



(1) Rotation on their base around their vertical long axis, so that the anterior 

 vocal process is rotated outwards and the muscular process backwards 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. 



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