In proximal and distal regions of the femur, the linea aspera widens to form an additional posterior surface. At the distal end of the femur, this posterior surface forms the floor of the popliteal fossa, and its margins form the medial and lateral supracondylar lines. The medial supracondylar line terminates at a prominent tubercle (the adductor tubercle) on the superior aspect of the medial condyle of the distal end. Just lateral to the lower end of the medial supracondylar line is an elongate roughened area of bone for the proximal attachment of the medial head of the gastrocnemius muscle (Fig. 6.52).