II. THE SWALLOW. Si 



bird's hand ; of which I rudely sketch the 

 contour of the bones at a. The innermost 

 fan, :b, is carried by the bird's fore-arm, from 

 wrist to elbow, b. 



The 'Strong humerus, c, corresponding to 

 our arm from shoulder to elbow, has command 

 of the whole instrument. No feathers are 

 attached to this bone ; but covering and pro- 

 tecting ones are set in the skin of it, completely 

 filling, when the active wing is open, the space 

 between it and the body. But the plumes of 

 the two great fans, A and B, are set into the 

 bones; in Fig. 8, farther on, are shown the 

 projecting knobs on the main arm bone, set 

 for the reception of the quills, which make it 

 look like the club of Hercules. The connection 

 of the still more powerful quills of the outer 

 fan with the bones of the hand is quite be- 

 yond all my poor anatomical perceptions, and, 

 happily for me, also beyond needs of artistic 

 investigation. 



73. The feathers of the fan A are called the 



primaries. Those of the fan B, secondaries. 



Effective actions of flight, whether for support 



or forward motion, are, I believe, all executed 



with the primaries, every one of which may be 



F 



