84 THE FLIGHT OF BIRDS 



the wing is bent the muscle lies in a slightly curved 

 form — we notice it when we are getting the meat 

 from between the two long bones of a chicken's 

 wing. It is straightened out when the wing 

 straightens, and this, combined with the outward 

 slope assumed by the feathers as they spread, 

 stretches the little tendons that arise from it and 

 are fastened to the feathers. The tendons slope 

 outward, away from the shoulder, and attach to 

 the under-side of the quills, or rather to the 

 fibrous tissue with which the quills are surrounded. 

 M. Alix (in his Appareil locomoteur des Oiseaux) makes 

 some of them at any rate attach to the further edge 

 of the lower face of the quills, and gives them the 

 credit for rotating the feathers during the down- 

 stroke, so that they press against one another and 

 make the wing impervious to air. But when I have 

 scraped these little tendons away in the wing of a 

 freshly-killed Pigeon I have found that, when I 

 extended the wing, the feathers still took their 

 proper position. The extending of the wing causes a 

 stretching of all the important stays — the ligaments, 

 the sheet of fibrous tissue, and these tendons — and 

 the ligaments may claim the largest share of the 

 credit for the spreading and marshalling of the 

 feathers. During the up-stroke the secondaries 

 are firmly tethered, but are no longer marshalled 

 for action. There are interspaces as there are 

 between the leaves of a folded fan that has seen 

 much service. The feathers being now no longer 

 pressed tight together, the air can pass between 

 them. When, however, the bird is flying fast and 

 the wings are lifted, not so much by muscles 



