431 



CHAPTER XXXI. 



VOICE. HOW PRODUCED. ITS EXISTENCE IN THE ANIMAL KINGDOM. 



THE HUMAN LARYNX. ITS CARTILAGES. THEIR ARTICULATIONS 



AND LIGAMENTS. CHORDS VOCALES. MUCOUS MEMBRANE. 



MUSCLES, EXTRINSIC AND INTRINSIC. ACTION OF THE LARYNGEAL 



MUSCLES. NERVES. ACTION OP THE LARYNX. THEORY OF VOCAL- 

 IZATION. CHEST VOICE. FALSETTO VOICE. SINGING. INFLU- 

 ENCE OF THE NERVES ON VOICE. SPEECH. 



THE high development of man's intellect, as compared with that 

 of the lower animals, would be of comparatively little advantage 

 without his peculiar endowment of speech. To this power, an 

 essential subsidiary is that of producing vocal sounds or voice; 

 which, however, he enjoys in common with a large number of the 

 lower classes. 



The phenomena of voice are produced by a very beautiful and 

 simple mechanical contrivance, the larynx, which is placed at the 

 top of the trachea, to take advantage, as an exciting force, of the 

 air emitted from the lungs during expiration. The air thus 

 expelled creates vibrations in certain tense and elastic membranes 

 (chorda vocales), the boundaries of a chink which is the orifice 

 at once of entrance and of exit for the supply of air to the lungs. 

 These vibrations generate voice. 



That the larynx is the organ of voice, is proved by the following 

 very obvious facts : first, the least alteration in the condition of 

 the mucous membrane covering the vocal chords, is invariably 

 accompanied by a change in the tone of the voice, e.g. hoarseness ; 

 secondly, ulcerative disease eating through one or both of these 

 vocal chords, destroys or greatly impairs the voice ; thirdly, opening 

 the trachea below the vocal chords, so as to divert the current of 

 air in expiration from the larynx, will destroy voice ; and fourthly, 

 section of the inferior laryngeal nerves, by which the influence of the 

 will is brought to bear on its muscles, and so the tension of the 

 vocal chords is regulated, destroys the voice ; lastly, by experiment 

 on the dead larynx, sounds may be produced resembling those of 



