OSTEOLOGY OF BIRDS 



299 



being enormously enlarged and welded together into a great bony 

 and membranous box, of wholly irregular, unsymmetrical contour. 

 Such a structure, represented in figure 29, is termed a tracheal tym- 

 panum or labyrinth. It is not a part of the voice organ proper, but 

 may act as a reverberatory chamber to increase the volume of the 

 sound, without however modulating it. Being chiefly developed in 

 the male, it is a kind of secondary sexual organ." 



In examining specimens of N e 1 1 i o n Caroline n sis, I 

 find the lower larynx to be gradually enlarged and funnel shaped, 

 being semidivided by an anteroposteriorly disposed plate of bone. 

 To the left side of this tracheal bifurcation, and communicating with 



Fig. 29 



a b 



Fig. 29 a, an inch of trachea, contracted to the utmost, the rings looking like 

 alternating half rings; b, the same, stretched to 2 inches, the rings evidently complete, 

 with intervening membrane [From Coues's after Macgillivray] 



Fig. 30 1, 2, left-hand, two tracheal rings, separate, as in figure 29 b; 2. 1, right- 

 hand, the same put together, as in figure 29, a. [From Coues's after Macgillivray] 



it below there arises a small osseous enlargement. It projects up- 

 wards alongside the bifurcation, and is perfectly rounded and 

 smooth, being without any opening above or at the sides. Inferiorly, 

 as I have just said, it possesses a common opening with the bifurca- 

 tion of the lower larynx. Its walls are thin and of uniform thick- 

 ness, the organ being very smooth and completely hollow within. 

 Such an appendage would admirably fulfil the function of a small 

 reverberatory chamber. This arrangement is practically repeated in 

 Dafila acuta, though the chamber is somewhat larger, but 

 only in proportion to the increased size of this species. In A i x 

 s p o n s a it is also much the same, but here the laryngeal enlarge- 

 ment is very globular in form, the opening communicating with 



