282 Summer Studies of Birds and Books 



certain about some points in the nature and working of 

 the instrument. 



Figures 1 and 2 show the way in which the sound is 

 generated in the syrinx, or lower larynx, of the bird. 

 The air from the lungs is blown into the windpipe 

 through two bronchial tubes, which are seen in Fig. 1, 

 looking something like the two legs of a pair of riding 

 breeches. At the point of junction of these two 

 bronchi, and stretching right across the fork, is a small 

 bony bar ; and supported on this bar is a membrane, 

 rising into the trachea and called from its shape the 

 semilunar membrane, which appears to vibrate like the 

 free reed of an organ-pipe as the wind reaches it from 

 the two bronchi. The currents of air from the two 

 tubes catch this membrane on each side of it, and thus 

 keep it, if the bird exerts force in expelling the wind, 

 in a state of strong tension and vibration. In Fig. 1 

 this membrane, or reed as I may be allowed to call it, 

 has been exposed to view by cutting away the outer 

 side of the left bronchus and the part of the trachea 

 immediately above it. It seems to be generally agreed 

 that this reed is the essential sound-generator in the 

 instrument. 



But the extraordinary resonance of the voices of 

 most birds can hardly be accounted for by the vibration 

 of this membrane alone ; and there seem to be two pro- 

 visions for securing this resonance. 



1. The cavity in which the "reed" is situated is not 

 surrounded, like the upper part of the trachea, by com- 

 plete bony rings, over which an elastic membrane is 

 stretched ; but the two bronchi, as they approach each 

 other, are composed of bony half-rings on the outer side, 

 while their inner sides, i.e. those next to each other, 

 consist of free elastic (or tympanic) membranes unsup- 

 ported by any stiff material and therefore capable of 

 being stretched tight by the wind blown from the 



