We may suppose then, though I do not speak with any certainty on so difficult a question, that the bird's instrument consists primarily of a vibrating reed, placed in a sound-chamber which is itself capable of vibration, and which is provided with an apparatus for increasing or decreasing the force of the wind brought to bear upon the reed. Fig. 3 needs no elaborate explanation. It is meant to illustrate the muscular apparatus which is attached both to the sound- chamber (syrinx) and to the wind- pipe (trachea), and which enables the bird to produce a great variety of notes by stretching and relaxing these, as I have explained on p. 127. The reader who is curious enough to examine these carefully, with the aid of Mr. Py craft's explanations and of the books I have mentioned above, will not fail to understand that they play the part of the fingers of a performer on a wind- instrument, by increasing and lessening the length of the pipe through which the musical sound is forced after being generated as described above. At the top of Fig. 1 Mr. Pycraf t has diagrammatically illustrated the way in which this is effected by drawing four tracheal rings in a state of relaxation and resting on each other, while below are two others separated by the tension of the elastic membrane covering them, which tension is the result of the action of the muscles shown in Fig. 3. It does not seem probable that the upper larynx, at the end of the windpipe next to the mouth and bill, has any effect on the musical sound, " otherwise than by dividing or articulating the notes after they have been formed in the lower larynx" (Sir E. Owen, quoted by Mr. Shufeldt in Myology of the Raven, pp.
44-47).
Printed by R. & R. Clark, Edinburgh.
