. Animal physiology. Physiology, Comparative; Physiology, Comparative. LARYNX OF BIRDS. 511 voices are louder than the roaring of lions, being distinctly audi- ble at the distance of two miles; and3 when a number are con- gregrated together, the effect is terrific. 685. In Birds, the situation of the vocal organ is very- different. The trachea opens into the Pharyux, as in Reptiles, by a mere slit; the borders of which have no other movement, than that of approaching one another, so as to close the aperture when necessary. But at the lower extremity of the trachea, just where it subdivides int
. Animal physiology. Physiology, Comparative; Physiology, Comparative. LARYNX OF BIRDS. 511 voices are louder than the roaring of lions, being distinctly audi- ble at the distance of two miles; and3 when a number are con- gregrated together, the effect is terrific. 685. In Birds, the situation of the vocal organ is very- different. The trachea opens into the Pharyux, as in Reptiles, by a mere slit; the borders of which have no other movement, than that of approaching one another, so as to close the aperture when necessary. But at the lower extremity of the trachea, just where it subdivides into the bronchial tubes, there is a sort of larynx or vocal organ, which is of very complex construction, especially in the singing-birds. The external surface of this larynx is represented in Fig. 249; its muscles, m, m, being left in their places on one side, and removed on the other. At 11, is seen the trachea ; at the lower extremity of which, t\ is a sort of bony drum, I, divided at its lower part by a parti- tion of the same material 0, Fig. 250), which is surmounted by a semi- t lunar membrane (c, Fig. 250). This drum com- municates below with the h> two bronchial tubes, I b\ b each of which has its own glottis and vocal cords; the c ;nnAW i:« ^f «.„.* ~f *1 • Fig. 249.—Larynx of a Rook. inner lip or one of these is seen at a (Fig. 250) ; and at me is shown a drum-like membrane, forming the inner wall of the bronchial tube, which probably increases the resonance of the voice. These parts are acted on by several muscles, the number of which varies according to the compass and flexibility of the voice in the different species; being very considerable in the most esteemed of the singing- birds, and being reduced to a small amount in those which have no vocal powers. In some, indeed, they are altogether absent ; and the state of the glottis can be influenced only by those muscles which raise and lower the whole trachea. 686. The vocal sounds produced by the action o
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