There are three long muscles in the posterior compartment of the thigh: biceps femoris, semitendinosus, and semimembranosus (Table 6.5)—and they are collectively known as the hamstrings (Fig. 6.63). All except the short head of the biceps femoris cross both the hip and knee joints. As a group, the hamstrings flex the leg at the knee joint and extend the thigh at the hip joint. They are also rotators at both joints.