SECTION V 

 VOICE AND SPEECH 



THE development of the analytical powers of the auditory appara- 

 tus 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 

 deal first with 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 determined by the length of 

 the tube which is attached to the reed, in the larynx the note pro- 

 duced 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 uppermost ring of the trachea, is 

 shaped like a signet ring, the small narrow part being directly forwards 

 and the broad plate backwards. The thyroid cartilage consists of 

 two parts or alae, 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 backward directions. The two arytenoid cartilages are pyramidal 



578 



