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XXVII. On the Physiology of the Human Voice. By John Bishop, Esq., F.R.S. 
Received April 30, — Read June 11, 1846. 
THE human voice is susceptible of several modifications, such as timbre, or quality, 
intensity, and pitch ; including those successive transitions of tone from one pitch to 
another which constitute melody. The organs of voice comprise the thorax with the 
muscles of respiration, the lungs, trachea, larynx, pharynx, mouth, tongue, nasal 
cavities, nerves, and blood-vessels. Of these, the thorax and lungs may be considered 
an air-chest or bellows, the trachea a portevent or air-pipe, and the glottis a com- 
plex reed. The trachea varies in length and diameter with the age and sex of indi- 
viduals, until they arrive at the adult period of life. By its structure the trachea is 
endowed with elasticity, together with the power of longitudinal extension and re- 
laxation, and of increasing or diminishing in diameter : the acoustic effect of these 
properties will presently be investigated. 
The sum of the diameters of the two bronchi is greater than that of the trachea ; 
by which adaptation the latter is more readily supplied with air during the vocaliza- 
tion of the breath. In all Mammalia, Birds, and Reptiles, the axes of the bronchi 
are inclined to that of the trachea at a greater or less angle. With reference to the 
voice, the larynx is the most important organ in the whole apparatus. The mouth, 
fauces, tongue, and nasal organs are not necessary to the production of voice; never- 
theless they exercise a considerable effect on its quality, and are indispensable for the 
production of articulate language. The thorax is sufficiently capacious to contain as 
much air after a full inspiration as will sustain the glottis in a state of vibration, 
when the tone is of moderate intensity, during the space of fifteen seconds, which will 
enable a person to pronounce in rapid succession from thirty to forty monosyllables 
at one expiration*. 
The phenomena of the voice of animals must at a very early period have afforded 
to physiologists proof of the susceptibility of membranous structures to enter into 
a state of vibration ; and it is now generally known that membranes, whether twisted 
into a cord like the string of a violin, or in the form of a parallelogram stretched in 
one direction as the vocal ligaments, or in that of discs stretched all round as the 
head of a drum, are all capable of producing musical sounds when properly excited. 
The theory of the vibratory movements of stretched membranous surfaces has 
occupied the attention of many of the most celebrated mathematicians, such as 
* Having already described in the Cyclopaedia of Anatomy and Physiology the minute anatomy of the larynx, 
the author considers it unnecessary to encumber this paper with details of that nature. 
