vil FLIGHT 201 
view each is connected by a little triangle of tendon 
with a muscle,! 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 antérieur, see p. 412 in App. Loc, des Orseaux, 
