In cross section, the shaft of the humerus is somewhat triangular with: anterior, lateral, and medial borders, and anterolateral, anteromedial, and posterior surfaces (Fig. 7.60).
The posterior surface of the humerus is marked on its superior aspect by a linear roughening for the attachment of the lateral head of the triceps brachii muscle, beginning just inferior to the surgical neck and passing diagonally across the bone to the deltoid tuberosity.