vii FLIGHT 257 



shifting the centre of gravity, none are, I believe, except 

 in quite exceptional birds, efficacious, and I doubt 

 whether any bird makes much use of them. The 

 problem, then, remains : when the body is suspended 

 from the wings and the centre of gravity lies at a point 

 farther back, how is a nearly horizontal position 

 maintained ? Mold up a bird, that has just been shot, 

 by the wings, and the hinder part of the body will drop 

 till the incline from the tail to the head (with the partial 

 exception explained on p. 227) is a very steep one. 

 This it is, no doubt, that has caused ornithologists to 

 look for some means by which the bird could at 

 pleasure move the centre of gravity forwards. The 

 true explanation is that during horizontal flight the 

 body is maintained in its position, with only a slight 

 upward incline, not by balance, but by muscular effort. 

 If you watch a Pigeon's movements and see how 

 instantaneously, without a motion of head or legs, he 

 changes the inclination of his body, you can hardly 

 doubt that it is the work of muscles. 1 The muscle 

 called the Latissimus Dorsi, which I have described 

 in connection with respiration, arises from the verte- 

 brae and attaches to the humerus (L. D. fig. 56). 

 During the downstroke it contracts, hauls upon the 

 wings, and thus raises the hinder quarters. The 

 enormous strength of the Great Pectorals prevents all 

 possibility of the wings yielding when thus pulled by 

 the Latissimus. The body must rise, since the wings 

 will not give. And, thus, indirectly, in addition to their 

 other work, the Great Pectorals help to bring the body 

 to the horizontal. When the wing rotates beyond a 

 1 See Bronn's Thicr-Reich, vol. u Aves," p. 229. 



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