THE ANATOMY OF BIRD-SONG. 113 



and at exactly the proper intervals for 

 the purpose in view. 



The so-called vocal cords in the syrinx 

 of a blue-bird (Sialia sialis) are less than 

 the twentieth of an inch in greatest ex- 

 tent. Indeed the free membrane of the 

 septum is scarcely discoverable with the 

 naked eye, and yet - the fife-notes of that 

 beautiful bird may be heard far across 

 the summer fields, sweet, clear, mellow 

 as the softest quaver of the flute d' amour, all 

 owing, as the great anatomists would have 

 it, to the vibrations of those deep-set infini- 

 tesimal membranous margins ! 



The chief stumbling-block of all the investi- 

 gators has been that they have taken it for 

 granted that birds have voices like those of 

 the mammals, and that consequently each 

 singer must have a set of vibrating vocal 

 cords somewhere in his breathing tube ; when 

 in fact the avian musician's syrinx has no 

 more need for vocal cords than had the 

 famous syrinx or Pan-pipe of the ancient 

 god. 



Let us again consider the act of whistling. 

 Note the fact that you can run the gamut 

 without perceptible change of the size or shape 

 of the mouth orifice, the sounds being graded 

 by controlling the size of the air column be- 

 hind the orifice. Now, the bird in whistling 

 controls both the size of the orifice and the 

 extent of the air columns above and below 

 the glottis. This gives him a range .and pow- 

 er of expression not to be approached by the 

 human whistler. He can open wide his 

 mouth and whistle, as does the quail, with 

 almost deafening shrillness and penetration, 

 or, closing his bill until a mere slit is seen be- 

 tween the mandibles, he can blow a dreamy 

 hautbois note, slender and refined as ever 



