200 THE STRUCTURE AND LIFE OF BIRDS chap. 



a muscle that arises from the ribs. A little nearer the 

 bases of the quills there is another ligament which, 

 instead of being pierced by them, runs along the lower 

 side only. These two ligaments, according to M. 

 Edmond Alix, get confounded at the hand and elbow, 

 but in Pigeons I have found them running still separate 

 beside the hand. 



The above description may possibly have given the 

 impression that the bones and ligaments supplied 

 some motive power. This can only come from muscles. 

 The forearm is put into line with the humerus by 

 muscular effort, and the effort required is greater since 

 the hand is necessarily extended by the same move- 

 ment, and the extension of the hand requires more 

 force since it involves the stretching of the ligaments 

 in which the feathers are set. Thus, indirectly, the 

 hand and the great feathers are prepared for flight by 

 the action of the triceps muscle that extends the fore- 

 arm. This must not be supposed to mean that there 

 is no special muscle to extend the hand. There is 

 one for this purpose arising from the further end of 

 the humerus. And it must be remembered that the 

 radius cannot by its sliding movement bring the hand 

 absolutely into line with the forearm : the finishing 

 touch must be given by the muscle just mentioned. 



It is a marvellous piece of machinery which thus 

 spreads the wings. But what is perhaps the most 

 remarkable thing with regard to the secondaries — the 

 great feathers that spring from the forearm — has yet 

 to be mentioned. They are shifted in such a way 

 that they prevent the passage of air during the down 

 stroke, but let it pass during the up stroke. With this 



