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-like 
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 
saying, 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 
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