VOICE AND SPEECH. 505 



or a strip of paper, parchment, or any other flexible substance, 

 be stretched between the fingers or otherwise, and a current of 

 air either from the mouth or a bellows be directed against one 

 of its edges, a clear musical sound will be produced, varying in 

 pitch according to the tension given it ; and, if a riband of thin 

 Indian rubber be employed, the sound will very much resemble 

 that of the voice, and be capable of an extensive range by varying 

 the tension. The itinerant exhibiters of Punch employ a silk 

 riband stretched between two arched pieces of tin, and, placing 

 this between the tongue and the palate, they without sounding the 

 voice pronounce all the articulations of speech by whispering, and 

 imitate the various inflexions of the voice by pressing more or 

 less on the thin sides, thus increasing or diminishing the tension of 

 the riband. Dr. Darwin was the first who appears to have re- 

 cognised the resemblance of this instrument to the ligaments of 

 the glottis. 



The vibrations of an elastic ligament set in motion by the air 

 being thus sufficient to account for the production of the voice, 

 we have only to examine the particular disposition of these 

 ligaments in the larynx, and the precise way in which the air acts 

 upon them. Each vocal ligament, stretched between the aryte- 

 noid and the thyroid, presents a sharp edge turned upwards and 

 inwards. Mr. Willis of Cambridge a has shown that, if a current 

 of air be made to pass between two stretched surfaces, they will 

 vibrate only when their free edges are parallel ; if they be turned 

 either outwards or inwards, the air will pass without producing 

 any sound. He hence infers that a certain position of the edges 

 of the ligaments is necessary for the air issuing from the lungs to 

 cause them to sound, and this vocalising position is determined 

 by the twisting motion of the arytenoid cartilages. 



" That every degree of motion in the glottis is directed by the 

 numerous muscles of the larynx is proved by the beautiful experi- 

 ment of tying or dividing the recurrent nerves, or the pneumono- 

 gastric b , and thus weakening or destroying the voice of animals." 



8 Of the Mechanism of the Larynx. Camb. Phil. Trans. 1832. 



b " Respecting this celebrated experiment, anciently made by Galen, consult 

 among others W. Courten, Philos. Trans. No. 335. 



Morgagni, Ep. Anatom. xii. No. 20. P. P. Molinelli, Comment. Institut. 

 Bonon. t. iii. 



J. Haighton, Memoirs of the Medical Society of London, t. iii." 



