RAVEN. 



273 



influence both the diameter and the length of the bronchi, 

 and the absurdity of the vulgar belief that to enable a bird 

 to "speak" the slitting of its tongue is necessary ought 



FIG. 9. 



FIG. 10. 



FIG. 11. 



hereby to be manifest. The principle on which the vocal 

 organs in Birds are framed is that which prevails in wind- 

 instruments generally; the notes in the ascending scale being 

 produced by a corresponding contraction of the diameter or 

 the length of the tube, and vice versa. 



