158 



ZOOLOGY. 



Fig. 114.* 



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, par- 

 takes seemingly of the quali- 

 ties of both kinds of instru- 

 ments. It has been proved 

 experimentally on the living 

 and dead larynx, that the 

 elastic cords (true ligaments 

 of the glottis) vibrate strongly 

 whilst the voice is being pro- 

 duced, and that the aperture 

 between them becomes much 

 contracted during the execu- 

 tion 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 musical 

 instruments is known to vary much, according as they are 

 constructed of wood, metal, or of other substances ; and cer- 

 tain modifications of the voice seem to be referable to a 

 hardening of the tissues composing the larynx, and especially 



* To show the rima of the glottis and the true vocal cords : d, epiglottis ; 

 c c, the two ary taenoid cartilages ; e e t true vocal cords ; between them is 

 the rima glottidis. 



