The biceps femoris muscle of the leg derives its name from having two heads of origin, long and short.
The long head arises from the medial facet on the ischial tuberosity in continuity with the tendon of origin of semitendinosus. The long head passes inferiorly to join the short head. By virtue of this origin alone, biceps femoris qualifies as a hamstring muscle.
The short head originates from the lateral lip of the middle third of the linea aspera and the lateral supracondylar line of the femur. Initially it is aponeurotic.
Upon union of the two heads, biceps femoris passes inferolaterally across the knee to insert into:
- the head of the fibula around the styloid process; the tendon envelopes the fibular collateral ligament
- the fibular collateral ligament
- lateral tibial condyle
Biceps femoris has several actions:
- long head alone: extension of the hip joint
- both heads:
- flexion of knee joint
- lateral rotation of lower leg at knee joint
The nerve supply of biceps femoris reflects the fact that the short head develops in the flexor compartment of the thigh - it is innervated by the common peroneal branch of the sciatic nerve (L5, S1). The long head is innervated by the tibial branch of the sciatic nerve (L5, S1).
The vascular supply is derived from the anastomoses of a number of arteries:
- perforating branches of profunda femoris
- inferior gluteal artery
- popliteal artery