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Boyer diss 2009 1046..

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notch and radial facet on the lateral side, there is not such a pronounced depression as on<br />

the opposite side. However, there is a sharp, faint groove caused by a narrow lip that<br />

protrudes from the posterior surface of the ulna. Farther distally, the lateral aspect of the<br />

shaft obtains a more distinctive, yet still shallow, depression. Toward the distal end of the<br />

bone the shaft develops two diverging dorsal ridges. The lateral one approaches the distal<br />

radial facet, while the other passes medial to it before meeting up with a surface that is<br />

contiguous with the radial facet and the carpal facet more distally. The more lateral of<br />

the two ridges appears to be the interosseous crest, while the medial one probably<br />

represents the medial edge of the area of origination for the pronator quadratus muscle<br />

(George, 1977).<br />

The distal end is marked by a dorsodistally-facing, convex facet for the distal<br />

radius and the lunate (see below). Distal to this, the styloid process sports a convex,<br />

dorsodistomedially facing facet for the triquetrum and pisiform of the proximal carpal<br />

row.<br />

Function.—The ulnar trochlea complements the morphology of the radius and<br />

humerus in the rather flat form and lateral orientation of its radial facet, which would<br />

have permitted the head of the radius to rotate on it. A dorsally projecting olecranon<br />

process suggests habitually flexed forearms and may even have limited the capacity for<br />

full extension, depending on the undistorted size of the olecranon process (Szalay et al.,<br />

1975). The only notable muscle scars are the groove on the medial surface of the<br />

proximal end, which likely provided a large area for insertion of the flexor carpi ulnaris<br />

muscle (George, 1977) and the ridge denoting the edge of the attachment for what was<br />

probably a well-developed pronator quadratus muscle (George, 1977). The presence of a<br />

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