THE VOICE. 825 



tensor, and therefore the most important, muscle of the larynx, has a sepa- 

 rate and distinct nervous supply. According to some authors the aryte- 

 noideus posticus also receives its nervous supply from this nerve ; but this 

 is denied by others. 



The inferior laryngeal or recurrent branch supplies all the other muscles. 

 When this nerve is divided the voice is lost, since the approximation and 

 parallelism of the vocal cords can no longer be effected. When in a living 

 animal both recurrent nerves are divided, the glottis is seen to become im- 

 mobile and partially dilated, the vocal cords assuming the position in which 

 they are found in the body after death, and which may be considered as the 

 condition of equilibrium between the dilating and constricting muscles. 

 During forcible inspiration the glottis passes from this condition in the 

 direction of more complete dilatation ; during forcible expiration, the change 

 is one of constriction. When the peripheral portion of one recurrent nerve 

 is stimulated, the vocal cord of the same side is approximated to the middle 

 line ; when both nerves are stimulated, the vocal cords are brought together 

 and the glottis is narrowed. Though the nerve is distributed to both dilating 

 and constricting muscles, the latter overcome the former when the nerve is 

 artificially stimulated. In the complete closure of the glottis, which is so 

 important a part of the act of coughing (p. 403), the group of muscles 

 which we have spoken of as constituting a sphincter is thrown into forcible 

 contractions by the recurrent laryngeal nerve. 



765. Though fundamentally a voluntary act, the utterance of a given 

 note is not affected by the direct passage of simple volitional impulses down 

 to the laryngeal muscles. So complex and coordinate a movement as that 

 of sounding even a simple and natural note requires a coordinating nervous 

 mechanism in which, as in other complex muscular actions, afferent impulses 

 play an important part. Auditory sensations, if not as important for an 

 accurate management of the voice as are visual sensations for the movements 

 of the eye, are yet of prime importance. This is recognized when we say 

 that such and such a one whose power over his laryngeal muscles is imperfect 

 " has no ear." 



A person may speak or sing in two kinds of voice. In the one the 

 sounds are full and strong, and the resonance chamber which is supplied by 

 the trachea, bronchi, and indeed by the whole chest, is thrown into power- 

 ful and palpable vibrations ; hence this voice is spoken of as the chest- 

 voice. The other kind of voice, called the falsetto, is thin and poor, deals 

 chiefly with high notes, and is not accompanied by the same conspicuous 

 vibrations of the chest. Much controversy has taken place as to the exact 

 manner in which these two voices are respectively produced. The prevailing 

 opinion teaches that in the chest-voice the vocal cords are somewhat thick, 

 their substance being thrust inward toward the median line by the contrac- 

 tion of the thyro-arytenoidei externi muscles, and the opening between them, 

 sometimes so narrow as to be almost linear, extends along their whole length. 

 In the falsetto voice, on the other hand, the vocal cords are said to be thin 

 and membranous, and the note to be given forth by a vibration, not of the 

 whole width of the cords, as in the chest-voice, but of the extreme edges 

 only, the lateral parts, though not absolutely at rest, vibrating with a differ- 

 ent rhythm. Though the whole larynx in the falsetto voice is stretched in 

 the antero-posterior direction, and the vocal cords correspondingly elongated, 

 the rima vocalis does not extend along their whole length ; at their posterior 

 part the cords are in contact, and indeed, according to some authors, the 

 high falsetto notes are produced by a sort of " stopping " of the cords. The 

 sense of effort which accompanies the falsetto voice indicates that the changes 

 in the larynx which bring it about are effected by some special muscular 



