The Biceps Femoris is a composite muscle. It originates from the ischial tuberosity (long head) and posterior aspect of the femur (short head). The muscle forms a common tendon which attaches to the head of the fibula. The tibial nerve innervates the long head of the biceps femoris. The common fibular nerve innervates the short head of the biceps femoris. The biceps femoris flexes and externally rotates the leg.