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 



Fifi. 8. 



Pig. 9, 



ta„l'J--. 



Fig. 10. 



Fio. 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. 



