THE MACHINERY OF FLIGHT 81 



It is essential, too, that there should be a large 

 expanse of bone, a firm foothold for the great flight- 

 feathers. The lizard, or lizard-like reptile, from which 

 birds are undoubtedly descended, had a very wobbly 

 hand. Even the Archaeopteryx, the most ancient 

 of birds, though it was beyond doubt a true bird and 

 not a bird-like lizard, had three long fingers which 

 show no sign of becoming fused together. With 

 birds as we know them, things are very different. 

 The three surviving metacarpals, or hand-bones, 

 enlarged by the fusing with them of the further 

 row of carpals or wrist -bones, are themselves fused 

 together, the two of the three that are the most 

 important fused both at the near and further ends. 

 Of the three surviving digits two are fused ; the 

 little thumb, that supports the bastard- wing, remains 

 independent and insignificant ; and the result of 

 all the fusing is that a broad, firm platform is 

 provided for the feathers. Thus we see that the 

 scaffolding of the wing when extended is remarkably 

 rigid in spite of its lightness ; its wide expanse of 

 feathers is remarkably elastic, and is planted on a 

 broad, firm base. 



The Spreading of the Wing. 



The machinery by which the wing is spread is well 

 worth study. The rapidity with which it does its 

 work is wonderful, and the accomplished result is 

 most beautiful. When the triceps muscle straightens 

 the wing at the elbow- joint, it is straightened also 

 at the wrist, not absolutely but nearly ; there are 

 special muscles for giving the finishing touch. Of 

 the two bones in the fore-arm the front one (the 



