01.09.2014 Views

Boyer diss 2009 1046..

Boyer diss 2009 1046..

Boyer diss 2009 1046..

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

mobility at the trapezoid-trapezium-scaphoid joints, meaning MC I could have moved<br />

quite extensively relative to the other metacarpals. This is similar to the mobility in many<br />

euprimate pollices (Napier, 1961). It differs in detail, however, in that hand types defined<br />

by Napier (1961) as “opposable,” obtain their mobility at the carpometacarpal joint, not<br />

at an intercarpal joint(s). The carpometacarpal joint of the first digit in P. cookei does not<br />

appear highly mobile due to the very close fit between the opposing facets of MC I and<br />

the trapezium.<br />

Trapezoid<br />

Description.—The right and left trapezoids are preserved (Fig. 4.11B, 12). Like<br />

the trapezium, it is the only example of this bone known for any plesiadapiform. The<br />

distal articular facet is rectangular in distal view and measures 4.13 mm by 2.15 mm. Its<br />

surface area is 8.2 mm 2 . It is gently saddle-shaped, with a concave dorsoventral profile<br />

and convex radioulnar profile. In radial or ulnar view it is true to its name-sake in having<br />

a trapezoidal outline, with a narrower proximal end than distal end. The radial surface<br />

articulates with the trapezium. This surface is also saddle-shaped with a concave<br />

dorsoventral profile and a convex proximodistal profile. The ulnar surface for articulation<br />

with either the capitate or the centrale (or both?) is helical at its distal end, such that<br />

toward its dorsal margin it forms an obtuse angle with the second metacarpal facet, while<br />

ventrally this facet is at an acute angle to the metacarpal facet. The proximodistal length<br />

of the bone is 2.4 mm. Only the dorsal surface of the trapezoid is largely non-articular.<br />

Function.—The saddle-shaped facets for the trapezium and MC II suggest that<br />

both of these bones were mobile with respect to the trapezoid.<br />

305

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!