OF THE HUMAN VOICE. 
553 
readily thrown into vibrations by the current of air, the sound is emitted by it alone, 
but it the blast is such that it throws them both into motion, they may both vibrate 
together, and by reciprocation produce a simple sound intermediate between the 
fundamental note of the two vibrating separately ; they may also emit two distinct 
sounds, or the blast being modified, the two sounds may be produced in succession. 
From these researches it appears, that membranous laminas, stretched in imitation 
of the thyro-arytenoid ligaments, will not only vibrate readily, but produce a range 
of musical tones. It has been remarked that sounds are most readily produced when 
the two laminas are stretched in the same plane, and that a smaller volume of air is 
required the nearer the edges of the laminas approach each other, and a still smaller 
one when their edges actually touch. De Kempelen states, that to produce sound, 
the edges of the glottis must be approximated to within T \th, or at least -j^th of an 
inch. These experiments upon artificial vibrating tongues perfectly agree with those the 
author has made on the larynxes of animals. Owing to the nature of the articulation 
of the thyroid with the cricoid cartilage, and the manner in which the crico-thyroid 
muscles act, an equal tension of both the thyro-arytenoid ligaments is simultaneously 
secured, supposing the arytenoid cartilages to be at the same time in corresponding 
positions, which is a necessary condition for the production of a synchronous vibratory 
motion in the two lips of the glottis. 
If the larynx of an animal is dissected out, and the vocal cords are stretched, they 
will vibrate like a piece of caoutchouc or leather in a current of air. In conducting 
these experiments, it is necessary to secure the same conditions as those which are 
required in the laminas above-mentioned ; for instance, the inner edges of the glottis 
must be turned towards each other till they are in the same plane and parallel to one 
another, before they will produce any sound ; hence we infer, that when the tension 
of the arytenoid ligaments takes place in the living animal, they turn upon their axes 
till their planes (which in the state of relaxation are inclined to the axis of the vocal 
tube) become perpendicular to it, and as the edges of the glottis approximate, and its 
chink is nearly or entirely closed up, they acquire the true vibrating position. The 
production of the most simple tones of voice requires the associated actions of a most 
extensive range of organs, and it is calculated that in the ordinary modulation of the 
voice, more than one hundred muscles are brought into action at the same time. 
The lungs having been first supplied with air by the muscles of inspiration, and the 
air in the chest and trachea having’ subsequently been condensed by the muscles of 
expiration, a portion of the edges of the glottis yields to its pressure, and is curved 
upwards, so as to form an angle with the axis of the vocal tube, leaving between them 
a narrow aperture through which the air escapes. The tension and elasticity of 
the vocal ligaments tend to restore them to the plane of the vibrating position; the 
air having been rarefied below the glottis during their elevation, becomes condensed 
on their depression, and the necessary force is again accumulated to re-elevate the 
vocal ligaments. An oscillating movement, consisting of a partial opening and closing 
MDCCCXLVI. 4 C 
