the Albatross, Gull, or Heron, there is a third series of long, 

 almost " quill-like " feathers running from the elbow to the 

 body, thus closing up what would otherwise be a gap between 

 the wing surface and the body, rendering flight impossible. 



The most important muscles of the wing are those which 

 have to provide the power for the down-stroke of the wing. 

 And these are the " pectoral " or " breast-muscles " — ^which 

 form such dainty meat in a roast fowl. Owing to their great 

 bulk the breast-bone itself would be insufficient to afford them 

 attachment. This is furnished by the development of a deep, 

 median keel, so that the breast-bone of a bird, such as a 

 pigeon, bears a fanciful resemblance, when seen in profile, to 

 the hull of a ship — unusually shallow — with a very deep keel. 

 The front end of the breast-bone supports two slender rods 

 of bone, and these in their turn support the long, sword-Uke 

 blade-bone, and the " merry-thought." 



The general appearance of this frame-work for the support 

 of the wing and its muscles can be seen in the adjoining 

 illustrations. But it must be remembered that in their 

 relative sizes and disposition these various parts present a 

 very considerable range of differences. That these differences 

 are correlated with different forms of flight goes without 

 sajdng, but, be it noted, no one, as yet, has attempted to 

 discover in what way they are related. Some of the readers 

 of this book may, perhaps, be tempted to try and solve the 



