Boyer diss 2009 1046..

epicondyle actually projects somewhat anteriorly, and the “anterior” surface of the distal
humerus faces somewhat laterally.
Function.—The humeral head, with its low but large tuberosities, suggests that the
shoulder was mobile. The large deltopectoral crest suggests the ability for powerful
adduction and extension of the humerus, as does the large, distally-positioned teres major
tuberosity (e.g., Gingerich, 1976). The flaring supinator crest provides ample area for
origins of the brachialis muscle anteriorly and the triceps posteriorly. The posterior arc
of the supinator crest gave the muscles that attached to it (extensor carpi radialis and
brachioradialis) a point of origination situated posterior to the brachial-antebrachial joint.
This would have given these muscles the mechanical capacity to “hyper-flex” the
forearm, beyond a position in which the arm and forearm axes were parallel (or fully
flexed). The deep supracapitular fossa is consistent with this capacity because it provides
a depression for the radial head to move into as the forearm is “hyper-flexed,” and allows
a more acute angle to be formed between the arm than if it were not present. The subspherical
shape of the capitulum suggests that the radius could rotate around its
proximodistal axis and contribute to supination and pronation of the hand. The capacity
for axial mobility in the forearm partly explains the pronounced medial epicondyle: the
large size and medial projection of the epicondyle increased the area of attachment and
leverage for the major pronators of the forearm that arose from it. The conical shape of
the ulna trochlea suggests that this joint was capable of flexion and extension only. The
relatively shallow olecranon fossa and posterior restriction of the capitulum suggest that
fully extended forearm postures were unstable or impossible. Lateral rotation of the
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