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. t 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 morphnlogists 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. 



t In the embryos of some birds, traces of a fourth finger liave been found. 



