SPEECH. 491 



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- 

 ment, we set the expiratory, mouth, and general vocalizing mus- 

 cles in readiness for the proper application of the air blast by a 

 voluntary act ; but the exact tuning of the vocal cords is accom- 

 plished in some measure reflexly by impulses corning from the 

 ear to a special coordinating centre, the education of which is 

 commonly in advance of the volition centres, and therefore can 

 only be controlled by the latter in persons specially educated to 

 music. Some persons who can sing a given note with promptness 

 and exactitude without any effort, would find much difficulty in 

 overcoming, by volition, the accuracy of this perfect reflex mech- 

 anism. In fact, a person with a good ear finds it difficult to sing 

 out of tune, even if he try. 



Though we feel that we have command over the pitch of our 

 sound-producing organ, we owe much to the aid of our sound- 

 appreciating organs and the nerve centres which they have in 

 connection with them. 



SPEECH. 



The variations in vocal sounds which give rise to speech are not 

 produced in the larynx, but in the throat, mouth, and nose. When 



