226 



PHYSIOLOGY FOR DENTAL STUDENTS. 



produce a sound of the ordinary pitch and loudness, while in 

 loud shouting much greater pressures are necessary. 



The sound of the voice, like any other sound, may vary in 

 pitch, loudness and quality. The range of pitch of the voice is 

 generally about two octaves, the pitch itself being determined 

 primarily by the lengths of the cords. This accounts for the 

 high-pitched voice of children, in whom the cords are short, and 

 the low pitch of the voice in men, in whom they are long. In 



-rf 



Fig. 34. Position of the glottis 

 preliminary to the utterance of 

 sound, rs, true vocal cord ; ar, ary- 

 tenoid cartilage ; b, pad of the epi- 

 glottis. (From Stewart's Physi- 

 ology. ) 



ar. 



Fig. 35. Position of open glottis. 

 1, tongue ; e, epiglottis ; ae, ary-epi- 

 glottidean fold ; c, cartilage of Wris- 

 berg ; ar, arytenoid cartilage ; o, 

 glottis ; v, ventricle of Morgagni ; 

 ti, true vocal cord ; is, false vocal 

 cord. (From Stewart's Physiology.) 



singing, three registers can be distinguished, the head, middle 

 and chest' registers. The deeper notes of the singer come from 

 the chest register, and are produced by the vibrations of the en- 

 tire cords, whereas in the upper registers only the inner edge of 

 the cords vibrate. 



The intensity or loudness of a vocal sound depends upon the 

 amplitude of the vibrations of the vocal cords, and this is pro- 

 portional to the strength of the expiratory blast. The pitch of 

 a note rises and falls somewhat with the intensity of the pres- 

 sure of the air, and, for this reason high notes are usually loud 

 notes. The quality of the voice, like that of a musical instru- 

 ment, depends on the overtones, or harmonics, that it produces. 

 For example, when a stretched string is made to vibrate, it not 

 only vibrates as a whole, but portions of it vibrates independent- 

 ly and gives off separate tones which are known as overtones. 



