34 



THE VOYAGE OF H.M.S. CHALLENGER. 



small size and does not exceed half the length of the second, to the upper half of the radial 

 border of which it is anchylosed. Its original separation as a distinct cartilage has been 

 proved by the observations of Gervais and Alix ^ on the wing of Eudyptes chrysocoine, 

 and indications of its original independence are visible even in the adult, in the presence 

 of an oblique groove, which is more pronounced on the outer than on the inner surface 

 of the metacarpal mass. This groove extends from the upper end of the metacarpus 

 obliquely downwards and forwards to the radial border of the bone which it meets 

 about the middle of its length. 



The second or middle metacarpal bone increases in breadth from its upper to its lower 

 end. Its radial border is anchylosed to the whole length of the first metacarpal, while its 

 ulnar border is immovably fused at its upper and lower extremities with those of the 

 third metacarpal bone. The shafts of these bones are separated by an elongated fissure. 

 The surfaces of the second metacarpal bone are flat and smooth. Its upper extremity is 

 provided with a convex articular surface, which articulates with the two carpal bones as 

 well as with the distal extremity of the ulna. The lower end possesses a slightly concave 

 articular surface adapted to the upper extremity of the first radial phalanx. 



The third metacarpal bone is slightly longer than the second, but is much more 

 slender. It is nearly cylindrical in form, and is fused at its extremities with the second 

 metacarpal. Its upper extremity articulates with the ulnar carpal bone, while its lower 

 possesses an oblique facet for articulation with the first ulnar phalanx. 



The metacarpus of different species varies only in size. Its dimensions are given 

 below in inches. 



