THE VOICE 



225 



and so relaxes the vocal cords. When the crico-thyroid muscles contract, 

 they cause the cricoid cartilage to rotate in such a manner as to tilt the 

 arytenoid cartilages backward, and so to put the cords on the stretch. Other 

 muscles are so arranged that they pull asunder the edges of the arytenoid 

 cartilages to which the cords are attached and thus open the glottis ; while 

 others, acting in the opposite direction, tend to bring the cords close to and 

 parallel with each other. 



The pitch of a note depends on the number of vibrations per 

 second : the more rapid the rate of vibration, the higher the pitch. 

 For example, 128 vibrations per second will 

 produce the bass C ; 256, the tenor C ; 

 512, the treble C; and 1,024, the octave 

 above ; and so on. If we stretch a wire 

 or string, we can make it vibrate by pluck- 

 ing it ; and by either shortening the string 

 or by increasing the stretching force, we in- 

 crease the rate of vibration, and so heighten 

 the pitch of the note produced. The rate 

 of vibration also depends on the thickness 

 of the string ; the thicker the string, the 

 less the rate of vibration. The more the 

 vocal cords are stretched, the higher the 

 pitch of the note given out. 



We may imitate the production of sound by the 

 larynx as follows : Take a glass tube, about f of 

 an inch in diameter, and grind one end down to 

 an angle of 45 on two opposite sides (see fig. 

 218). Now stretch over these ground edges two 

 thin strips of elastic band, leaving only a narrow- 

 space between, and secure by tying round with 

 thread. By blowing a current of air between these 

 stretched bands they are made to vibrate, thus 

 producing a sound ; and by altering the length 

 of the tube, and changing the stretching force of 

 the elastic bands, we can vary the pitch of the 

 note. 



g. 2 1 8. Illustrating 

 the manner of pro- 

 ducing a Musical 

 Sound by sending a 

 current of air between 

 two stretched Elastic 

 Bands. 



The quality of the note depends on 

 various conditions, among which may be 

 mentioned the shape of the mouth, the 

 position of the tongue, the communica- 

 tion or non-communication between the pharynx and the nasal 

 cavities, the position of the larynx, &c. 



In young persons the larynx of the male is constructed exactly like that of 

 the female ; but on reaching a certain age the larynx of the male rapidly 

 increases in size, becoming more prominent in the front of the throat. The 

 enlargement of the larynx causes a corresponding increase in the length of the 

 vocal cords ; hence the change in the pitch of the voice. 



Q 



