Chap, xxxiii.] THE PRODUCTION OF VOICE. 449 



tension of the cords, and so elevate the pitch, while 

 the action of the thyro-arytenoid muscles will have 

 a reverse effect by pulling up the thyroid cartilage, 

 and lessening the tension of the cords. In the pro- 

 duction of tones of very high pitch, doubtless the 

 overlapping of the posterior parts of the cords by the 

 action of the lateral crico-arytenoid muscles, aided by 

 the arytenoid muscles, will have some effect by limit- 

 ing the vibrations to a smaller part of the cords. 

 While pitch is regulated in such ways, loudness is 

 affected by the greater or less degree of force of the 

 outgoing current producing movements of greater 

 or less amplitude. All this, however, as it appears, 

 is bat a small and elementary part of the production 

 of voice. The larynx above the cords, the pharynx, 

 and the cavities of the nose and mouth play a very 

 important part in the process. They act the part of 

 resonators, and reinforce the sound of one or other of 

 -the overtones produced by the vibrations of the cords. 

 Now these resonating passages and cavities are not 

 of a fixed shape or size, but can be altered in various 

 ways, so as to be capable of resounding now to one 

 note, now to another. Helmholtz remarks that they 

 admit " of much variety of form, so that many more 

 qualities of tone can be thus produced than in any 

 instrument of artificial construction." Thus the form 

 of the air passages above the cords will determine the 

 quality of sound, not only for separate individuals, 

 but also for the same individual at different times. 

 The important part played by these resonating pas- 

 sages is shown by Helmholtz's elaborate investigations 

 on the production of vowel sounds. The different 

 vowels may be produced when the vocal cords are 

 vibrating the same number of times per second, that 

 is, when they are sounding the same fundamental 

 note, and with the same intensity. The only differ- 

 ence necessary is in the form of the mouth, so that for 



D D 7 



