174 Bird Comrades 



he opens his mandibles quite widely, sometimes almost 

 to the fullest possible extent. 



However, the expansion and contraction of the throat 

 orifice, no doubt, produce still more marked variations 

 in the tones of the vocalist; yet it must be borne in mind 

 that closed or partly closed mandibles will obstruct the 

 passage of the air from the throat, while open mandibles 

 will permit of a full passage of the air current, arid the 

 tones will vary accordingly. Besides, the roof of the 

 bird's mouth is grooved or convex, and therefore the char- 

 acter of the sounds will be somewhat dependent upon the 

 position and movement of the upper mandible. 



And then there is the bird's tongue, which is con- 

 stantly in motion while the musical rehearsal is going on. 

 Throughout its entire length it can be raised and lowered 

 at the bird's will, or be made to quiver and roll, and by 

 this means the air column forced up from the lungs is 

 manipulated in a wonderful way, producing in some cases 

 an almost unlimited variety of modulation. 



Within the bird's neck two elastic tubes run down 

 from the mouth into the chest. One of them is the gullet 

 or sesophagus, which is the channel through which the 

 bird's food descends into the crop and gizzard. The 

 other little cylinder lies in front of the gullet, and is called 

 the windpipe or trachea, and reaches down to the lungs, 

 which are the bellows furnishing the wind for the avian 

 pipe organ. As Dr. Coues says, the trachea is " com- 

 posed of a series of very numerous gristly or bony rings 

 connected together by an elastic membrane," and is sup- 



