THE MACHINERY OF FLIGHT 



71 



through a little tunnel formed by the three bones, 

 which meet at the shoulder -joint, and after passing 

 through the tunnel attaches to the upper side of the 

 humerus, near to its preaxial or front edge. Its 

 action is to erect the wing upon its pivot. Attaching 



Fig. 21. 



Humerus of right wing of Eagle. Actual length 6f inches. D : 



Flat area near the front margin of the under-surface, where the 



tendon from the Depressor muscle attaches. 



where it does, it must necessarily bring the wing 

 into the proper position for beginning the next stroke 

 with its front edge looking in the direction of flight. 



