330 Mr Willis on the 



equal extent to that of the human voice cannot be obtained from 

 edges of leather, but this scale is much greater in India rubber than 

 in leather, and the elasticity of them both is so greatly inferior to 

 that of the vocal ligaments, that we may readily infer that the 

 great scale of the latter is due to its greater elastic powers. To 

 obtain various notes from the glottis, therefore, it is only necessary 

 to vary its longitudinal tension after its ligaments have been placed 

 in the proper position. 



As, however, during breathing the air passes freely in and out 

 of the lungs through the identical apparatus by which the notes 

 are produced, the passage we have been considering, or glottis, 

 must be capable of assuming the form of a large and free aper- 

 ture ; since it is certain, from the freedom with which the air is 

 inhaled and exhaled, that it is not compelled to pass through so 

 small a slit as the glottis appears to be during vocalisation. 



The passage is also capable of being shut so close by its own 

 small muscles that all the exertions of the powerful abdominal 

 muscles acting upon the diaphragm to compress the lungs and 

 condense the air in the trachea are not capable of forcing it 

 open . 



The production of a musical note takes place instantaneously, 

 at the pleasure of the individual. The breath has been previously 

 traversing the passage in silence, and at our will some change is 

 immediately made in the larynx, which produces the note, and 

 this certainly depends upon something more than the mere closing 

 of the passage, because we can make the aperture of the passage 

 pass through all degrees of contraction up to absolute closing 

 during the expiration of the breath without producing any sound, 

 except the usual rushing noise of a forcible current of air passing- 

 through a narrow aperture. 



