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Boyer diss 2009 1046..

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Metacarpal II description.—MC II of set 1 (Figs. 4.14B, 15) is represented by the<br />

complete left side element and a fragment of the proximal end of the right side. The left<br />

side has a straight shaft that becomes progressively mediolaterally wider from its<br />

proximal end to its distal end. This is especially noticeable just beyond the proximal<br />

articular surface, because the girth of the shaft increases abruptly here. The proximal<br />

articular surface for the trapezoid slopes so that its ulnar edge projects farther proximally<br />

than its radial edge. The articular surface for the trapezoid also faces slightly dorsally<br />

relative to the metacarpal shaft orientation. The trapezoid facet is saddle-shaped and has<br />

a surface area of 7.7 mm 2 . The ulnar side of the proximal end facet is separated into<br />

ventral and dorsal regions. Both regions probably articulated with both MC III (distally)<br />

and the capitate (proximally). The strip of articular surface connecting the dorsal and<br />

ventral facets articulated with the capitate. The radial side of the proximal end appears to<br />

be devoid of articular facets. Both the radial and ulnar sides of the proximal end are flat<br />

without any substantial convexity or concavity. In ventral view, the distal end has three<br />

prominent keels: two lateral and one median. The radial side of the distal end profile<br />

slopes away from its distal apex more gradually than the ulnar side. In dorsal and lateral<br />

view, it can be seen that the distal articular surface extends onto the dorsal side of the<br />

element and is hemispherically convex. This hemispherical articular surface is laterally<br />

flanked by deep pits (for collateral ligaments). The proximolateral margins of the pits are<br />

formed by large tuberosities.<br />

MC II of set 2 (Fig. 4.16A) is similar to MC II of set 1, just described, but they<br />

clearly come from two different individuals (both are left side elements) and two<br />

different species. Major differences that distinguish the two include the following: (1)<br />

310

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