The interosseous membrane serves as the floor of the anterior compartment of the leg (Fig. 16-13). This is a closed space; the boundaries are the anterior fascia of the leg in front, the interosseous membrane behind, the fibula laterally, and the tibia medially. This space as well as the lateral compartment permits little, if any, expansion of the structures contained within, whereas the posterior compartment is a loosely contained space with a relaxed and redundant fascia. The tight fascial investment of the muscles contained in the anterior and lateral compartments helps to prevent undue swelling of the muscles during exercise and thereby facilitates venous return.