The biceps femoris is a long muscle lying on the lateral border of posterior aspect of human thigh. Thus, it belongs to the posterior group of thigh muscles, together with the semitendinosus and semimembranosus muscle. It has two heads, a long and a short head, which fuse together to form a single common belly.
The long head of the biceps femoris muscle arises from the ischial tuberosity by a narrow, flat tendon. The short head originates from the lateral lip of linea aspera of the distal half of femur. Then the two heads get together to become a strong muscle belly, which stretches down along the posterior lateral border of thigh, parallel and next to the semitendinosus muscle. The distal portion of the biceps femoris becomes a long narrow tendon, which curves around the lateral epicondyle of femur to be inserted into the head of fibula.
However, some bands of its distal tendon runs almost horizontally to be inserted into the edge of superior articular surface of the tibia. The lower bursa of the biceps femoris muscle is lodged between its tendon and the lateral ligament of the knee.
Action/Function
It extends the thigh at the hip-joint. It also flexes the leg at the knee-joint, rotating it laterally.
Innervation
The long head of the biceps femoris in innervated by branches of the tibial and sciatic nerve (S1, S2). The short head receives branches from the common peroneal nerve (L4, L5, S1).
Blood Supply
It receives oxygenated blood from the medial circumflex femoral, perforating, and popliteal artery.
Above, a schematic picture of posterior side of right thigh, showing the biceps femoris muscle. You can observe that its proximal (upper) portion is covered by the gluteus maximus.