320 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 
Fra. 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, 
