3io 



HUMAN PHYSIOLOGY 



female, makes the voice deeper. The tension of the cords 

 may be varied by the action of the crico- thyroid muscle. 



The power of varying the pitch of the voice differs greatly 

 in different people. The average difference between the 

 lowest and the highest note which the ordinary individual 

 can produce is about two octaves. 



The quality of the sound depends upon the overtones 

 which are made prominent by resonance in the pharynx, 

 nose, and mouth. By varying the shape and size of these 

 cavities and more especially of the mouth, the quality of 

 sound may be considerably varied. 



Singing Voice. This is often classified by its average pitch 



A i u 



FIG. 143. Changes in the Shape of the Mouth in Sounding the Vowels A, 7, U. 



and by its quality into bass and tenor in males, and contralto 

 and soprano in females. 



The true or chest voice is produced by a blast of air from 

 the chest setting the cords into vibration, but the falsetto 

 voice, which is generally higher in pitch than the true 

 voice, is probably produced by vibrations of the edges of 

 the cords. 



Articulate Speech. Spoken language is produced by 

 varying the resonating chambers of the pharynx, nose, and 

 mouth, and thus modifying the sounds produced in the 

 larynx. Whispered speech is produced by setting in vibra- 

 tion in the resonating chambers a stream of air which has 

 not been allowed to act upon the vocal cords. 



In articulate speech two classes of sounds may be dis- 



