The biceps femoris (also biceps femoris muscle, latin: musculus biceps femoris) is a two-headed muscle of the thigh located in the posterior region of the thigh.
The long head of the biceps femoris originates from the back part of the ischial tuberosity (on the superior ramus of the ischium), while the short head of the biceps femoris arises from the lateral lip of the linea aspera (on the posterior surface of the shaft of the femur).
Both heads of the biceps femoris insert onto the head of the fibula.
The functions of the biceps femoris are flexion and external rotation of the knee. The fibers of the long head of the biceps femoris also aid in extension of the thigh.