234 



HABITS OF BIRDS. 



the conformation of the windpipe. In Bewick's swan 

 (Cygnus BewicMi, YARREL), in the adult state, the 

 windpipe, which is of equal diameter throughout., 

 enters the keel of the breast-bone, through which it 

 makes its way to the end, where, inclining upwards 

 and outwards, it passes into a cavity formed in the 

 body of the bone by the separation of the bony plates, 

 and producing a convex protuberance on the inner 

 surface of the breast-bone. In this cavity the wind- 

 pipe assumes a horizontal direction, and makes a 

 considerable curve, reaching within half an inch of 

 the posterior edge of the breast-bone. It then re- 

 turns to the keel, along the upper part of which it 

 passes to the exterior edge of the bone, over which 

 it is reflected so as to enter the body of the bird, and 

 become attached to the lungs. On the other hand, 

 in the wild or hooping swan (C. ferus), the wind- 

 pipe never assumes a horizontal direction, and does 

 not even penetrate within the keel to the extent of 

 one half of the breast-bone*. 



Trachea of C. Bewickii. 



* Trans, of the Nat. Hist. Society of Newcastle, for 1831, 

 and Zool. Journ. v. 258. 



