288 Summer Studies of Birds and Books 



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. 



