IO 



THE STRUCTURE AND LIFE OF BIRDS chap. 



strain is put upon them. The Radius is a very 

 slender bone, the Ulna much thicker, with small but 

 well-marked projections at the points where the great 

 feathers grow. Of the nearer row of carpal bones 

 there are only two (RC and UC), whereas there are 

 three found in the lizard ; in the bird the small inter- 

 mediate one has disappeared, and also the central bone 



Fig. 4.— Hand of (a) Haiteria Lizard; {b) Chick, 

 ci, near row of carpals; C2. farther row of carpals ; ce, central bones — there 

 are often two ; d i, 2, 3, 4, 5, digits ; mc, metacarpals ; p, pisiform bone, originally a 

 tendon ; r, radius ; u, ulna. 



beyond it. Of the more distant row there is not a 

 sign in the mature bird, but, if we examine the skeleton 

 of an embryo, it may be made out. In a young chick- 

 there are still two free bones to represent it (C 2, fig. 4). 

 In the adult these have been fused with the Meta- 

 carpals beyond. The tendency to fusion, or, as it is 

 technically called, ankylosis, is found in many parts of 



