86 THE FLIGHT OF BIRDS 



back, in the armpit, and fastens the wing to the 

 bird's side. 



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 Pis. xi and xn). 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 



