vn FLIGHT 201 



view each is connected by a little triangle of tendon 

 with a muscle, 1 which arises from the upper-arm bone 

 at the end further from the body and attaches its 

 other extremity to one of the wristbones and also to 

 one of the metacarpals further on. Working un- 

 opposed, it bends the wrist. When the wing extends, 

 its resistance tightens up the wrist-joint and helps it 

 to bear the strain of flight. When the wing is bent, it 

 lies in a slightly curved form. It is straightened out 

 when the wing straightens, and this, combined with the 

 sloping of the feathers outwards from their bases, as 

 they spread, stretches the little tendons that arise from 

 it and are fastened to the feathers. These little tendons 

 slope outwards, away from the shoulder, and passing 

 under the quills fasten to their further side (fig. 54). 

 When tightened, they rotate the feathers so that the 

 near side of the vane is pressed hard against the off 

 side of the one that overlaps it, thus preventing the 

 passage of air. During the up stroke the tendons 

 relax and the feathers are no longer pressed tight 

 together, so that the air can now pass through them. 



It is worth remarking that though the Triceps 

 controls the wings from the elbow joint to the hand, 

 yet that the two united fingers and all the feathers 

 upon them are not under its sway, but depend upon 

 their own muscles to extend them, lower them and 

 raise them — small movements the importance of which 

 it is so difficult to estimate. The bastard wing also is 

 moved by its own muscles. 



The wing-area is greatly increased by two mem- 



1 The muscle is called flexor carpi ulnaris by M. Alix ; the 

 cubital anteneur, see p. 412 in App. Loc. des Qiseaux, 



