THE MACHINERY OF FLIGHT 75 



than is the Elevator, but not so much as the De- 

 pressor. In most birds that I have examined, I have 

 found that the leg muscles show less ridging and 

 granulation even than the Elevator. But the 

 Moorhen makes great use of his legs. He is both a 

 swimmer and a runner. When not swimming he is 

 generally walking on the grass beside his pond or 

 stream, busied with the search for worms. 



Before I leave the subject of quality of muscle I 

 must point out that the inferiority of the pale to the 

 red has been noticed also in thoroughbred horses. 

 Mr. J. B. Robertson, in his very interesting paper 

 on the Principles of Heredity applied to the Racehorse 

 (p. 22), writes : "The pale fibres greatly predominate 

 in the tissues of a pure sprinter, and the red fibres 

 in those of a stayer." 



The big muscles, the work of which I have 

 described, are all massed upon the sternum. Even 

 the muscles which bend or straighten the wing at 

 the elbow spring not from the humerus or upper- 

 arm bone, but from the top of the coracoid and the 

 anterior end of the shoulder-blade respectively. I 

 once cut off the wing of a domestic Pigeon as close 

 as possible to the body and found that it scaled just 

 under £ oz. The bird weighed 13i oz. Thus the 

 two wings together accounted for just under one- 

 eighth of the whole. It is wonderful that such 

 strength can be combined with such lightness. And 

 not only is the wing, as a whole, light ; what weight 

 it has belongs almost entirely to the bones and muscles 

 of the near part. This Pigeon's wing balanced, 

 when rested on a wire 2J inches from its base 

 and 10 inches from its tip. The great primary 



