584 PHYSIOLOGY 



register, and the head register. The deeper notes of any individual 

 voice are always produced in the chest register. Observation of the 

 vocal cords shows that when producing such notes the glottis forms 

 an elongated slit, all the muscles which close the glottis and increase 

 the tension of the cords being in action. The vocal cords are relatively 

 thick and broad and can be seen to vibrate over their whole extent. 

 When singing with the head voice the vibrations of the cord are 

 apparently confined to their inner margins ; the aperture of the 

 glottis is wider in front than behind, so that more air escapes during 

 phonation by this method than in the production of the chest voice. 



In order to change the pitch of the note the following means are 

 probably employed in the larynx : 



(1) Alteration in the tension of the vocal cords. 



(2) Alteration in the length of the part of the vocal cords which 

 is free to vibrate, which can be accomplished by the approximation 

 of the arytenoid cartilages to one another, or by their approximation 

 to the thyroid cartilage. 



(3) The alteration in the shape of the vocal cords, which is deter- 

 mined by the activity of the different portions of the internal thyro- 

 arytenoid muscles. 



(4) The varying pressure of the blast of air passing through the 

 glottis. 



The loudness of the tone produced is practically proportional 

 to the force of the blast of air employed. The quality or timbre 

 of the voice depends not so much on the vocal cords as on the accessory 

 resonating apparatus, represented by the trachea and chest and by 

 the cavity of the mouth. The greater part of the education involved 

 in voice training is directed to the modification of the shape of the 

 mouth cavity, so as to secure the greatest possible fulness, i.e. richness 

 in overtones, of the tone produced in the larynx. 



THE MECHANISM OF SPEECH 



The sounds employed in speech, viz. vowels and consonants, are 

 produced by modifying the laryngeal tones by changes in the shape of 

 the mouth and nasal cavities. In whispering speech there is no 

 phonation at all, but the sound is produced by the issue of a blast of 

 air through a narrow opening between the lips, between the tongue and 

 soft palate, or between the tongue and the teeth. 



The vowel sounds are continuous, whereas the consonants art- 

 produced by interruptions, more or less complete, of the outflowing 

 air in different situations. The vowel sounds, u, o. a, e, i (pronounced 

 oo. oh, ah, eh, ee), are tones, i.e. are produced by a regular series of 

 vibrations. These tones take their origin in the mouth cavity, as 

 can be shown easily by the fact that we can whisper these sounds 



