ii SKELETONS OF BIRD AND REPTILE u 



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 1 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 I am taking it for granted for the nresent that this digit 

 corresponds to our thumb. See p. 42. 



