CHAPTER VII. 



SPECIAL MUSCULAR MECHANISMS. 



SEC. 1. THE VOICE. 



A BLAST of air, driven by a more or less prolonged expiratory 

 movement, throws into vibrations two elastic membranes the 

 chordce vocales. These impart their vibrations to the column of 

 air above them, and so give rise to the sound which we call the 

 voice. Since the sound is generated in the vocal cords, we may 

 speak of them and of those parts of the larynx which decidedly 

 affect their condition as constituting the essential vocal apparatus ; 

 while the chamber above the vocal cords, comprising the ventricles 

 of the larynx with the false vocal cords, the pharynx and the 

 cavity of the mouth, the latter varying much in form, constitute a 

 subsidiary apparatus of the nature of a resonance-tube, modifying 

 the sound originating in the vocal cords. In the voice, as in other 

 sounds, we distinguish : (1) Loudness. This depends on the 

 strength of the expiratory blast. (2) Pitch. This depends on the 

 length and tension of the vocal cords. Their length may be 

 regarded as constant, or varying only with age. It consequently 

 determines the range only of the voice, and not the particular note 

 given out at any one time. The shrill voice of the child is 

 determined by the shortness of the cords in infancy, and the 

 voices of a soprano, tenor and baritone are all dependent on the 

 respective lengths of their vocal cords. Their tension is on the 

 contrary variable; and the chief problems connected with the 

 voice refer to variations in the tension of the vocal cords. (3) 



