86 THE FLIGHT OF BIRDS 
back, in the armpit, and fastens the wing to the 
bird’s side. al 
It is worth while noticing that though muscles 
springing from the body in the main control the 
movements of the whole wing, yet there is a good 
deal of local independence. ‘There are niceties of 
adjustment which depend on local muscles. Though - 
the triceps extends the upper arm, the fore-arm’ 
and the hand, yet the two united fingers, and with 
them the great feathers they carry, are not under 
its sway but depend upon special muscles to spread — 
them to the full and carry out minor movements. 
The little bastard-wing has also its own muscles— 
more muscles than one would expect to be at the 
service of so insignificant a piece of machinery. 
Structure of a Flight-Feather. 
For the bird flight without feathers is obviously 
an impossibility. If the scales of the bird’s reptilian 
ancestors had remained mere scales, the ancestors 
would have remained reptiles still, condemned to 
crawl the earth. The scale has been glorified till 
it is hardly recognisable. First comes the quill with 
the dried remains of the pulp—the pulp that was 
there when it was alive and growing—still visible 
within it. Above is the rachis, or shaft, grooved 
down its front face (see Pls. x1 and xm). From 
the shaft spring the barbs sloping towards the tip of 
the feather, from the barbs branch out the barbules 
or radii. From those of the barbules that are on 
the far side of the barb (the side farther from the 
base of the feather) spring the barbicels (diminutive 
of a diminutive !) that fasten barbule to barbule and 
