II SKELETONS OF BIRD AND REPTILE II 
the bird’s skeleton, and may be regarded as a most 
marked characteristic. The bone formed by the fusion 
of the farther row of carpals with the metacarpals 
forms a broad slab on which rest many of the most 
powerful feathers of the wing. Its compound nature 
is described by its name of Carpo-metacarpus, or 
wrist-hand bone (CM fig. 2). Of the five metacarpals 
only three remain, and these three are fused together 
at their bases. Farther on they separate and can be 
easily distinguished. The first is only a slight pro- 
jection from which the thumb! springs, the second is 
long, strong, and nearly straight, the third after de- 
scribing a curve fuses again with the second at its 
farther end. The very short thumb consists of two 
phalanges only, the last being very small. It fre- 
quently has attached to it a claw suggestive of 
reptilian ancestry. The second and third digits are 
far away at the ends of their long metacarpals, 
attached firmly one to the other so that neither can 
move separately. The second is formed of three 
phalanges, of which the first is broad and plate-like, 
the last very minute ; the third digit is insignificant, 
with only a single phalanx. In digits I and II the 
final phalanx is often missing. The two united 
fingers have some slight power of movement, which 
many birds turn to account; but in no part of 
the hand is there what can in any ordinary sense 
be called a joint. The wrist-joint, also, has much 
changed its character. It allows the hand to move 
freely towards the place where the fifth digit (or 
1 am taking it for granted for the vresent that this digit 
corresponds to our thumb. See p. 42. 
