LIMBS 



167 



In the carpus, at least seven elements are recognisable. In 

 the proximal row is an intermeclio-radiale and a centro-ulnare, 

 each of which consists of two parts in the embryo. In the distal 

 row there are also two elements, one of which (carpale 2 + 3) is 

 evidently primarily double : the other corresponds to carpale 4. 

 In early stages four distinct metacarpals can be seen, and these 



-Klaue 



Klaue 



B 



FIG. 133. CARPUS OF EMBRYO OF Sterna wilaoni. A, STAGK AT WHICH 

 OSSIFICATION BEGINS ; B, STAGE IMMEDIATELY T.EFORE HATCHING. (After 

 V. L. Leighton. ) 



r, distal carpals ; Ktaite, claw ; Had, radius ; rad, intermedio-radiale : Ufn, 

 ulna ; -tiln, centro-ulnare ; II V, metacarpals (in B, / V and V have become 

 fused). 



seem to correspond to the 2nd-5th rather than to the lst-4th : the 

 5th metacarpal soon fuses with the 4th (Fig, 133). 



The distal carpals become fused with the corresponding meta- 

 carpals, thus forming a carpomeiaearpus (Figs. 132, 133), and in 

 the adult only the two proximal elements remain separate as a 

 radiale and an ulnare. The three metacarpals themselves become 

 united proximally, and the second ('///) and third (IV) distally: 

 they only bear a limited number of phalanges at their free ends. 



Claws were present on the terminal phalanges of all three 

 digits in Archaeopteryx (Fig. 49). In certain recent adult Birds 

 (e.g, Chauna) the first digit (//) bears a claw, and more rarely 



