zoo THE STRUCTURE AND LIFE OF BIRDS cwap. 
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 
