Like the tibia, the shaft of the fibula is triangular in cross section and has three borders and three surfaces for the attachment of muscles, intermuscular septa, and ligaments (Fig. 6.85). The interosseous border of the fibula faces and is attached to the interosseous border of the tibia by the interosseous membrane. Intermuscular septa attach to the anterior and posterior borders. Muscles attach to the three surfaces.