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 
Humerus of right wing of Eagle. Actual length 63 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. 
