On the voice of birds / [Philip Bury Duncan].

  • Duncan, Philip Bury, 1772-1863.
Date:
Between 1830 and 1839?]
Catalogue details

Licence: Public Domain Mark

Credit: On the voice of birds / [Philip Bury Duncan]. Source: Wellcome Collection.

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    living animal, shows at the moment when it cries, that its voice is formed by the vibrations of the vocal chords. The following appears to be the most probable explanation of the successive process of the human voice. The air driven from the lungs passes first through a pretty large canal. This canal soon grows nar¬ rower, and the air is compelled to pass through a narrow slit, the two sides of which are vibrating plates, and which, like the plates of a reed, alter¬ nately permit and prevent the passage of air, and determine by these alternations sonorous undula¬ tions in the current of the air which is contained. The ligaments of the glottis acquire the power of vibrating like reeds, only in proportion to the con¬ traction of the thyro-arytenoid muscles, and conse¬ quently when these muscles are not contracted, there will be no voice. Experiments on animals completely accord with this doctrine. If the recur¬ rent nerves attached to these muscles be cut, the voice is entirely lost; if only one be cut, the voice is but half lost. The intensity of the voice depends, like that of all other sounds, upon the vibrations of the vocal chords; for the more forcibly the air is driven from the chest, the greater is the extent of their vibra¬ tions, and the longer these chords are, (that is, the larger the larynx,) the more vigorous will be the vibrations. A vigorous person, whose chest and larynx are large, is in the most advantageous condition for in¬ tensity of voice. If this person falls sick, and loses