91 



malous figure, in consequence of a thick and short process which is sent off from 

 the ulnar side of its base, which gives it the appearance of being bent at a right 

 angle. By this form it acquires two distinct proximal articulations or points of 

 support : one at its base, or in the normal position, by which it joins that pro- 

 cess of the scaphoides which represents the trapezium ; the other on the before- 

 mentioned process, with its plane at right angles to the basal articulation and 

 abutting upon the proximal end of the adjoining metacarpal. An oblong sub- 

 angular eminence extends along the dorsal surface of the first metacarpal ; a 

 convex rough protuberance projects from the palmar aspect of its base, and is 

 divided from a smaller protuberance beyond it by a deep transverse groove. 

 The two articular surfaces at the proximal end of the bone are quite flat ; the 

 distal articular surface is a simple elliptical smooth convexity, occupying little 

 more than the ulnar half of the distal end of the bone ; two small smooth an- 

 gular surfaces at the lower end of the articulation indicate the sesamoid bones 

 at the palmar aspect of this joint of the thumb. 



The second metacarpal bone, besides being longer than the first, is proportion- 

 ally thicker and stronger, especially at its distal extremity, which is character- 

 ized by its large, vertically extended, trochlear articulation. The proximal end 

 of the bone is triangular, with the apex towards the palm, and obliquely trun- 

 cated to form the surface abutting upon the os magnum : the principal part of 

 the base is occupied by the surface, gently convex below, concave above, for 

 the trapezoides. On the radial side of the base is the subtriangular flat surface 

 against which the first metacarpal abuts ; the ulnar side of the bone is excavated 

 by a deep elliptical cavity for the reception of a corresponding convex process 

 of the middle metacarpal. The dorsal non-articular surface is transversely 

 quadrate, slightly concave, with the two proximal angles raised into tuberosities : 

 the palmar surface of the bone is rough and convex. The distal trochlea is 

 most extended from above downwards, is convex in this direction, with a strong 

 ridge produced, with a slight obliquity, from along the middle line, becoming 

 rather sharp at the lower end of the joint ; on each side of this rising the 

 trochlear surface is concave transversely, broadest on the radial side, and ter- 

 minating on each side by a sharp lateral ridge. The great vertical length of 

 this articular surface indicates the extent of motion of the claw in that direc- 

 tion, while its form equally demonstrates the strength of the joint and the close 



M 2 



