Biceps femoris muscle

The biceps femoris (Latin for " two-headed muscle of the femur " on German as the " hamstrings " or " hamstring " ) is an skeletal muscle with two muscle heads.

In the even-toed ungulates of the muscle to the gluteus superficialis muscle is fused to the gluteobiceps. In the four-footed mammals a minor tendon of the biceps femoris ( calcaneus tendon, Tendo accessory ) radiates into the Achilles tendon.

Function

The long head acts both on the hip joint as well as on the knee joint as well as the other two muscles of the hamstrings muscles, Mm. semitendinosus and semimembranosus. In the hip joint it causes extension and external rotation of the knee joint flexion. The short head only affects the knee joint. Thus both muscles flex the knee joint and can rotate the lower leg outward at the knee flexed.

In the four-footed mammals, the effect of the biceps femoris muscle is even more complex. In addition to the extension and abduction of the hip joint it acts in the attached leg ( " support leg " ) on the extension of the knee with (because of the lower leg is fixed on the ground), the lifted leg ( "Hang leg " ) to act as knee flexors. Due to its calcaneal tendon of the muscle also acts as extensors of the ankle.

The involvement of the biceps femoris muscle (and the other two muscles of the hamstrings muscles, Mm. Semitendinosus and semimembranosus ) on the extension of the knee joint, however, is well known to the people under the concept of Lombard 's paradox.

Varieties

Sometimes the short head is missing. The external rotation in the flexed knee joint must then be executed by the caput longum alone.