20 



The Bird 



the two principal divisions into which the flight-feathers 

 are divided: the primary feathers, or those growing on 

 the fingers and wrist-bones, and the secondaries which 

 sprout from the bone of the forearm. The several feathers 



Fig. 255. — Young Green Heron, showing various divisions of wing-feathers. 



supported by the thumb are also very distinctly shown. 

 When a wing is greatly elongated it is the secondary 

 feathers which are increased in number, the two extremes 

 being represented by the hummingbird and the albatross, 



