MECHANISM OF THE VOICE. 149 



Lastly, superiorly the upper aperture of the larynx (which 

 must not be confounded with the rima glottidis) is protected 

 by a nbro-cartilage, of a triangular shape, called epiglottis, 

 by means of which, during deglutition, the larynx is still 

 further protected from the accidental passage of food or drink 

 into the air tubes, the effect of which accident, unless 

 instantly relieved, is suffocation. 



299. Mechanism of the Voice. In the ordinary state 

 the air passes and repasses the larynx, and no sound is heard ; 

 but when the muscles of the larynx contract so as to modify 

 the vocal cords as to tension, and to affect the diameter of the 

 rima glottidis, sounds are immediately produced. The cele- 

 brated Galen divided in a living animal the nerves proceeding 

 to the larynx, and first showed the phenomenon to depend on 

 muscular action influenced by the nerves. By cutting the 

 true vocal cords the voice is destroyed altogether. 



300. Most physiologists are disposed to think that the 

 voice is solely produced by the vibrations of the true vocal 

 cords acting in the manner of the reed of the hautboy ; this 

 would make of the human organ of voice a wind instrument. 

 Others speak of it as if it more resembled the violin, or was 

 a stringed instrument. The human voice, which surpasses 

 all musical instruments, partakes seemingly of the qualities 

 of both kinds of instruments. It has been proved experi- 

 mentally on the living and dead larynx, that the elastic cords 

 (true ligaments of the glottis) vibrate strongly whilst the 

 voice is being produced, and that the aperture between them 

 becomes much contracted during the execution of acute or 

 shrill sounds ; they may even be made to touch for a large 

 part of their course. They differ also in length in man and 

 woman, and in children. 



301. The intensity of the voice depends partly on the 

 force with which the air is expelled from the lungs, partly on 

 the size of various parts of the larynx, partly on the facility 

 with which its various parts vibrate. In some mammals, 

 large cells exist, communicating with the larynx, and it is to 

 these cells that the strength of the voice is attributed. This 

 structure is met with in the ass, and more especially in the 

 apes of America, called howlers. 



302. The timbre (quality) of the voice seems to depend 

 partly on the physical properties of the ligaments of the 

 glottis and walls of the larynx, partly on those of the air- 

 tube following the larynx. The quality, for example, of 



