• 53 



In the Mylodon, the radius is not only thicker in proportion to its length, but is more 

 extensively and deeply impressed by the muscles of the fore-arm, especially on the back 

 part of the bone. The tuberosity for the insertion of the biceps is further from the 

 proximal joint, and augments the power of the muscle in the same degree : the proximal 

 articular cavity is of an oval form. 



Carpus. — The carpus (Plate XXI. s — u) consists of seven bones, four in the proximal 

 and three in the distal row. 



Scapho-trapezium. — The first of the proximal row (ib. s) includes the bone (ib. t\ 

 answering to the first of the distal row in Man and most Mammals, and is consequently 

 a 'scapho-trapezium' (s, t)*, as it is also in the Sloths, the Mylodon and Scelido- 

 therium. It is of an irregular triangular shape, with its base applied to the 'lunare' 

 (ib. I), and with the apex somewhat twisted. It presents a broad convex articular 

 surface (ib. s) for the outer half of the concavity of the radius ; and this surface is con- 

 tinuous with a crescentic one of about one inch in breadth, which covers the proximal 

 part of the side of the bone next the os lunare. The palmar or anterior horn of the 

 crescent is continuous with an oval flat articular surface joining the os magnum (ib. g) : 

 the opposite or dorsal horn is separated by a rough tract from a convex subquadrate 

 surface which also articulates with the os magnum. On the outer side of this surface, 

 and, like it, on the fore-part of the bone, is a surface concave in one direction and convex 

 in the opposite direction, for articulation with the small trapezoides (ib. z). External 

 to this, the fore-part of the produced and twisted apex of the bone, which represents the 

 trapezium, articulates with the stunted metacarpal of the pollex (ib. m i), chiefly by 

 ligament, but also by a small elliptical flat surface which seems to have been covered 

 with articular cartilage. Between the two facets for the os magnum the bone is deeply 

 excavated and has been perforated by blood-vessels. 



Lunare. — The 'os lunare' (Plate XXI. I) offers, as in Man, some rude resemblance 

 to a crescent ; its proximal surface, very convex from before backward and rather convex 

 from side to side, is wholly covered by the smooth articular surface which plays upon 

 the ulnar half of the terminal cavity of the radius ; and this surface is continued upon 

 the radial side of the bone to form there the crescentic tract, adapted to the similarly- 

 shaped tract on the scaphoid. The inner horn of this tract is continuous with the surface, 

 convex at the fore-part, then deeply concave from before backwards, for the os magnum 

 (ib. g) : this articular surface is continuous with a similarly deeply excavated and irre- 

 gular one on the ulnar half of the fore-part of the bone, which is subdivided into three 

 facets, the middle one for the os cuneiforme, the two smaller ones for two parts of the 

 os unciforme. 



Cuneiforme. — The ' os cuneiforme ' (ib. c), which is the smallest of the three proximal 

 carpals, presents at its radial side a triangular convex surface for articulation with the 



• This is the bone called 'cuneiforme' in Cuvieb's chapter on the Megatherium, and which is marked r 

 in the copy of Dr. Pander's figure of the Madrid skeleton introduced into plate 217, fig. 3, of the edition of 

 the ' Ossemens Fossiles,' 8vo, 1835, here cited. 



