SOUND PRODUCTION AND SPEECH 



741 



This optical method employed for determining the rate of vibration is 

 that of the stroboscope. Lesions of the vocal cords or of the neuro- 

 muscular mechanism which prevent their vibration cause loss of voice. 

 The height of a tone in such a two-lipped reed pipe as the larynx 

 depends on the length, thickness, and tension, of the cords, and to a 

 certain degree on the strength of the air-blast. 



FIG. 451. EXAMINATION OF THE LARYNX BY THE LARYNGOSCOPE. 



The shorter and more strongly stretched the membrane, the higher 

 is the tone; women and children have a smaller larynx and shorter 

 cords, and hence high-pitched voices. At puberty there is a rapid 

 increase in growth, and the breaking of the voice is due to the want 



Soft 

 Palate 



FIG. 452. To ILLUSTRATE THE MANNER IN WHICH A VIEW OF THE INTERIOR OF THE 



LARYNX is OBTAINED. 



of co-ordination between the innervation and the muscular mechanism 

 which has so rapidly increased in strength. The new apparatus has 

 to be practised by the growing lad. 



The structure of the larynx has been evolved to allow the ready 

 alteration of the length and tension of the cords. Four cartilages 



