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 Archeopteryx, 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 
G 
