514 BRITISH FOSSIL REPTILES. 



the parts, and in the degree in which that surface is convex in the attached bone. The 

 two metacarpals were thus closely and ligamentously united, in a way and to an extent in 

 which I have not observed the homologous bones in any recent Crocodilian or Lacertian. 

 The anconal margin of the rough tract projects, ridge-like, along the proximal half of the 

 bone. The anconal surface of the shaft begins, at an inch and a quarter from the 

 proximal end, to be smooth, and is convex in both directions, but least so longitudinally. 

 The ulnar surface of the shaft is roughened, but in a less degree than the radial one ; the 

 distal articular surface, single at its anconal half, where it is feebly concave, feebly concave 

 transversely at its mid part, and much more convex in the opposite direction, has that 

 curvature continued upon two lateral portions toward the thenal aspect of the bone, 

 divided by an intervening channel. 



The distal articular surface also inclines slightly to the radial side, where it projects 

 beyond that surface of the shaft ; it does not extend beyond the ulnar surface. It thus 

 repeats the tendency to the bend radiad noticed in the second metacarpal, but here 

 limited to the distal end. 



The fourth metacarpal (PI. 48, iv, m) is 5 inches 6 lines in length ; it is more com- 

 pressed than the third, especially at the anconal part ; the ulnar surface sloping anconad to 

 meet the radial one, leaving the upper surface to be represented as a rounded border; thus, 

 the shaft is trihedral, not quadrilateral. The proximal articular surface is 2 inches ancono- 

 thenally by 1 inch 5 lines transversely. The chief part of tlie articular surface traverses 

 that end of the bone in its long axis, with a strong convexity transversely, which passes into 

 a flatter facet at the ulnar side ; this ridge-like disposition of the chief articular prominence 

 was probably wedged between the os magnum and uiiciforme. The ulnar flatter surface 

 would articulate with the latter bone ; in advance of this is a rougher tract, of small 

 extent, for ligamentous articulation with a fifth metacarpal. The radial side of the fourth 

 metacarpal is flattened and rough for junction ligamentously at its proximal part with the 

 contiguous metacarpal ; with an interval in the rest of the extent left by the concave 

 curve, which this surface describes lengthwise, and which interval was probably filled up 

 by looser ligamentous tissue. 



The distal articulation, 1 inch G lines across, and the same in the opposite direction 

 at the radial side, resembles in character that of the third metacarpal, but with an opposite 

 obliquity tending to direct the toe which it supported more ulnad. 



The corresponding metacarpal is preserved of tlie right fore-foot. 



To either the third or the fourth digit belongs a proximal phalanx, 2 inches 6 lines m 

 length, 1 inch 8 lines in transverse breadth of the proximal end, 1 inch 6 lines in the 

 same breadth of the distal end, which supports a well-defined, smooth, shallow trochlear 

 surface, 1 inch I line transversely by 10 lines ancono-thenally ; it closely resembles the 

 proximal phalanx of the second digit, but is rather narrower in proportion to its length, 

 and shows greater disparity of size between the two distal tuberosities on the thenal 

 surface. It may belong to the right paw. 



