NERVOUS MECHANISM OF VOICE. 493 



a different quality, which are called head notes, since their pro- 

 duction is not accompanied by any vibration of the chest wall. 

 The physical contrivance by means of which this falsetto voice is 

 brought about is not very clearly made out. The following are 

 the more probable views: (1) It has been suggested that in 

 falsetto only the hin edges of the cords vibrate, the internal 

 thyro-arytenoid muscles keeping the base of the cord fixed; while 

 with chest tones a greater surface of the cord is brought into 

 play. (2) The cords are said to be wider apart in falsetto than 

 in chest notes, and hence the trachea, etc., ceases to act as a reso- 

 nator. (3) Or the cords may be arranged so that only one part 

 of them, the anterior, can vibrate, and thus they act as shortened 

 cords, a " stop " being placed on the point where the vibrations 

 cease, by the internal thyro-arytenoid muscle. 



The production of a falsetto voice is distinctly voluntary, and 

 is probably dependent upon some muscular action in immediate 

 relation to the cords, for it is always associated with a sensation 

 of muscular exertion in the larynx as well as with changes that 

 take place in the conformation of the mouth and other resonating 

 tubes. 



NERVOUS MECHANISM OF VOICE. 



The nervous mechanism by means of which vocal sounds are 

 produced is among the most completely coordinated actions that 

 regulate muscular movements. 



Like respiration, vocalization at first seems a simple voluntary 

 act, sounds of various kinds being produced at the command of 

 the will of the individual. No doubt the respiratory muscles, 

 which work the bellows of the voice organ, are under the control 

 of the will so long as the respiration is not interfered with. The 

 mouth and throat muscles which shape the resonating tube are 

 also voluntary. But the intrinsic muscles of the larynx are only 

 voluntary in a certain sense, while in another they are distinctly 

 involuntary, as may be seen in spasm of the larynx ; for they 

 are, in part at least, controlled by impulses which arise at the 

 organ of hearing and pass to some coordinating centre which 

 arranges the finer muscular movements necessary to produce a 

 certain note. When we sing any note struck on a musical instru- 



