94 The Bird 
wing-tip around and make flight impossible. So but 
two of these small bones are free in our chicken’s wrist, 
although in the small chick several more (six in all) are 
separate. 
If we double back our fourth and fifth fingers and 
imagine that they have disappeared, extend our other 
three fingers and then suppose that all our wrist-bones, 
save two, have fused with the three long bones leading 
to the base of our thumb, index and middle fingers,* we 
will have an idea of the condition of our chicken’s wing, 
and indeed there is very little difference between this and 
the wings of all other birds.—| We have two separate 
bones in our thumb, and three in each of the next two 
fingers, and the bird has the same number, except in 
its third finger, in which there is but one. The principal 
value of this comparison is to show us that the bird, 
even in its most characteristic and specialized organ,— 
the wing, is not physically so unlike ourselves as we 
might at first glance suppose. When a bird folds its 
wing against its body, the joints are bent sharply, and 
the Z, formed by the elbow and the wrist, almost closes 
up. We can place our arm and hand in much the same 
position. 
If we move our arms slowly up and down, little by 
little greatly increasing the speed, we will realize how 
much greater strength and rigidity the whirring wings 
* Some morphologists homologize the fingers of a bird’s wing with the 
second, third, and fourth digits of a pentadactyl hand. The question is still 
a mooted one. 
+ In the embryos of some birds, traces of a fourth finger have been found. 
