54 



lunare; and at its fore-part an irregular concavo-convex oblong surface for the unci- 

 forme (ib. «). Its proximal surface is tuberous and rough for ligamentous attachment 

 to the ulna, except where the smooth articular surface for the os pisiforme is situated : 

 this surface is in great part convex. 



In the Mylodon the os cuneiforme is the largest of the carpal bones. 



Pisiforme. — The os pisiforme (Plate XXI. p) is conical with an obtuse apex, having 

 on its base the articular surface for the os cuneiforme, and with the rest of its exterior 

 surface more or less irregular, for implantation of a tendon and ligaments. 



Trapezoides. — The homologue of the trapezium being connate with the scaphoid, and 

 noticed in the description of that compound bone, the trapezoides (ib. z) is the first 

 independent carpal bone of the distal row. It is the least of the carpal series, and is a 

 relatively smaller and flatter bone than in the Mylodon: the proximal or scaphoidal 

 surface is convex transversely, concave from behind forward, and plays in a correspond- 

 ing concavo-convex surface in the scaphoid. The distal surface is almost wholly convex: 

 both surfaces are joined by a small articular facet on the radial side of the bone, which 

 is adapted to a corresponding facet in the small metacarpal bone of the thumb ; and by 

 a more extended articular surface on the ulnar side of the bone for junction with the os 

 magnum. 



Magnum. — This bone, arbitrarily so termed, comes next after the trapezoides and 

 pisiforme, in the order of size, being much inferior to the other carpals. It is almost 

 wholly covered by smooth articular surfaces. The small non-articular rough surface (ib. g) 

 exposed upon the back of the wrist is of a transversely extended hexagonal figure, with 

 the outer and inner sides the shortest. The surface for the lunare is concave anteriorly, 

 but very convex in the greater part of its extent. It is continuous at its radial border, 

 with the two surfaces, one concave, the other flat, for the scaphoides ; and at its ulnar 

 border with the flat surface for the unciforme. The concave scaphoidal surface is con- 

 tinuous with the surface for the trapezoides, which is much narrower than is the same 

 surface in the Mylodon, the scaphoidal surface being broader than in the Mylodon. 

 The largest articular surface is that for the base of the great middle metacarpal, which 

 is slightly convex except at its fore-part, which is produced into a cone. 



Unciforme. — Of all the carpals the os unciforme (ib. u) differs most in form from that 

 of the Mylodon ; it is a thick transversely extended bone, the free tuberous surface on 

 the back of the wrist being hexagonal, with the two inner and the two outer sides very 

 short : one of the outer sides is formed by a protuberance separating the articular sur- 

 faces for the os cuneiforme and fifth metacarpal, which meet at an acute angle in the 

 Mylodon. 



The proximal oblong concavo-convex surface for the cuneiforme is continuous, at the 

 radial side of the bone, with the surfaces for the lunare and os magnum ; and the latter 

 with the broad surface along the distal part of the base which is obscurely divided into 

 three facets, the middle and largest for the base of the fourth metacarpal, the next in 

 size for the outer facet or the base of the third metacarpal, and the outermost and 



