80 THE FLIGHT OF BIRDS 
take place. The rigidity there is more easily 
brought about owigg to the fact that of the two 
small rows of wrist-bones the further one has been 
fused with the hand-bones. When the fore-arm 
is brought into line with the upper arm, the hand 
also falls almost into line and is held tight in that 
position by ligaments. As soon as the wing is 
flexed at the elbow, it bends also at the wrist— 
bends backward, that is, towards where digit 5 
Fie. 23. 
Skeleton of wing of Adjutant (from the elbow). D 1, 2, 3: 
Digits 1, 2, 3. MC 1, 2, 3: Metacarpals 1, 2, 3. R: Radius. 
RC: Radial carpal. Ul: Ulna. UC: Ulnar carpal. The 
marks left by the little pockets in which the secondary feathers 
are planted can be seen on the ulna. 
would be if it existed—and then at the latter joint 
much freer upward movement also is possible. And 
so the wing is rigid when rigidity is wanted, and 
pliant when pliancy is in demand (see fig. 23). 
