206 



ANATIDJJ. 



tached to the lungs in the usual manner. This is the state 

 of development in the oldest bird I have met with. The 

 degree next in order, or younger, differs in having the 

 horizontal loop of the trachea confined to one side only of 

 the cavity in the sternum, both sides of which cavity are 

 at this time formed, but 4he loop of the tube is not yet 

 sufficiently elongated to occupy the whole space ; and the 

 third in order, that on the right of the three representa- 

 tions shown below, from a still younger bird, possesses only 

 the vertical insertion of the fold of the trachea ; yet in this 

 specimen the cavity in the posterior portion of the sternum 

 already exists to a considerable extent. 



These are the peculiarities of structure which belong to 

 the tube and the sternum. The bronchiae are very short ; 

 but the flexible part intervening between the bone of di- 

 varication and the bronchial rings is considerable, pro- 

 ducing an effect to be hereafter noticed ; this elongated, 



