WEALDEN DINOSAURS. 511 



the radius ; the concavity was adapted to part of the distal end of the nhia, but leaving 

 the ulnar end of the distal convexity of that bone (PI. 46, fig. 1, /c) for probable adaptation 

 to an OS pisiforme. The distal surface of the unciforme shows the concavity for an os 

 magnum, and a well-defined flatter surface for a small unciforme. 



The metacarpal of the pollex (PI. 4S, I, m) is 4 inches in length ; 2 inches 5 lines 

 across the broadest part of the proximal end ; 2 inches across the corresponding part of 

 the distal articulation. Both these dimensions are in the direction of the transverse 

 breadth of the paw, the bone being subdepressed. The proximal articulation is a shallow, 

 circular cavity continued radially upon a rough, angular production of that end of the 

 bone. The opposite side of the articulation is produced into a broader roughened surface 

 for syndesmotic union with the base of the next metacarpal. 



The anconal sui'face of the bone (shown in PI. Ill), for an inch or more in advance of 

 the distal end, is roughened by longitudinal grooves and ridges : the surface then continues 

 smoothly to the distal convexity ; but shows, on each side near that surface, evidence of 

 the powerful lateral ligaments connecting this metacarpal with the first phalanx. 



On the radial side is a rough oval pit, an inch in long diameter, with the proximal 

 border prominent and forming an angle in the radial outline of the bone. There is a 

 similar projection on tlie ulnar side, but it forms the proximal end of a triangular 

 tuberosity. 



The thenal surface of the bone is more or less rough, and is divided by a low medial 

 prominence into two facets. 



The distal articulation is of an oval shape, convex in a greater degree than the 

 proximal articulation is concave; it is 2 inches across transversely, IJ inch in the opposite 

 direction, or from the anconal to the thenal surface. The plane of both proximal and 

 distal articular surfaces is not quite transverse to the axis of the bone, but rather oblique 

 from the ulnar forward to the radial end. The least transverse diameter, at the middle of 

 the shaft of this metacarpal, is 1 inch 8 lines. 



The metacarpal of the pollex of both right and left fore-feet has been obtained. 



The first phalanx of the pollex (PI. 46, 1) is broader and more depressed, in proportion 

 to its length than is the metacarpal which supports it. Its proximal concavity is smaller 

 and more shallow than the convexity to which it is adapted, though this appearance may 

 be in some degree due to the abrasion of the margins. That part which is preserved 

 equally bespeaks the strength of the ligamentous attachment with the metacarpal ; it is 

 most produced on the radial side of the bone {a), as if ossification had extended there 

 along the lateral ligament toward the metacarpal. The opposite or ulnar roughened sur- 

 face is broader, more tuberous, but less produced. 



The anconal surface of the bone is less regularly convex transversely than in the 

 metacarpal ; the mid part being raised so as to divide it from the surface on each side, 

 which is flatter transversely and shghtly concave lengthwise. 



The smooth surface on the radial side is continued along a notch at the radial border 



2d 



