The biceps femoris () is a muscle of the

thigh In anatomy, the thigh is the area between the hip (pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of bone tissu ...

located to the posterior, or back. As its name implies, it consists of two heads; the long head is considered part of the

hamstring A hamstring () is any one of the three posterior thigh muscles in human anatomy between the hip and the knee: from medial to lateral, the semimembranosus, semitendinosus and biceps femoris. Etymology The word " ham" is derived from the Old ...

muscle group, while the short head is sometimes excluded from this characterization, as it only causes knee flexion (but not hip extension) and is activated by a separate nerve (the peroneal, as opposed to the tibial branch of the

sciatic nerve The sciatic nerve, also called the ischiadic nerve, is a large nerve in humans and other vertebrate animals. It is the largest branch of the sacral plexus and runs alongside the hip joint and down the right lower limb. It is the longest and widest ...

Structure

It has two heads of origin: *the ''long head'' arises from the lower and inner impression on the posterior part of the

tuberosity of the ischium The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, or as a pair the sitting bones, is a large posterior (anatomy), posterior bone, bony protuberance on the superior r ...

. This is a common tendon origin with the

semitendinosus muscle The semitendinosus () is a long superficial muscle in the Posterior compartment of thigh, back of the thigh. It is so named because it has a very long tendon of insertion. It lies posteromedially in the thigh, superficial to the semimembranosus. ...

, and from the lower part of the

sacrotuberous ligament The sacrotuberous ligament (great or posterior sacrosciatic ligament) is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends. Structure It runs from the sacrum (the lowe ...

. *the ''short head'', arises from the lateral lip of the

linea aspera The linea aspera () is a ridge of roughened surface on the posterior surface of the shaft of the femur. It is the site of attachments of muscles and the intermuscular septum. Its margins diverge above and below. The linea aspera is a prominent ...

, between the

adductor magnus The adductor magnus is a large triangular muscle, situated on the medial side of the thigh. It consists of two parts. The portion which arises from the ischiopubic ramus (a small part of the inferior ramus of the pubis, and the inferior ramu ...

and vastus lateralis extending up almost as high as the insertion of the gluteus maximus, from the lateral prolongation of the linea aspera to within 5 cm. of the lateral condyle; and from the lateral intermuscular septum. The two muscle heads joint together distally and unite in an intricate fashion. The fibers of the long head form a

fusiform Fusiform (from Latin ''fusus'' ‘spindle’) means having a spindle (textiles), spindle-like shape that is wide in the middle and tapers at both ends. It is similar to the lemon (geometry), lemon-shape, but often implies a focal broadening of a ...

belly, which passes obliquely downward and lateralward across the

to end in an

aponeurosis An aponeurosis (; : aponeuroses) is a flattened tendon by which muscle attaches to bone or fascia. Aponeuroses exhibit an ordered arrangement of collagen fibres, thus attaining high tensile strength in a particular direction while being vulnerable ...

which covers the posterior surface of the muscle and receives the fibers of the short head. Inferiorly, the aponeurosis condenses to form a tendon which predominantly inserts onto the lateral side of the head of the fibula. There is a second small insertional attachment by a small tendon slip into the lateral condyle of the

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

. At its insertion the tendon divides into two portions, which embrace the fibular collateral ligament of the

knee-joint In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...

. Together, this joining of tendons is commonly referred to as the ''conjoined tendon'' of the knee. From the posterior border of the tendon a thin expansion is given off to the fascia of the leg. The tendon of insertion of this muscle forms the lateral hamstring; the common fibular (peroneal) nerve descends along its medial border.

Variations

The short head may be absent; additional heads may arise from the ischial tuberosity, the linea aspera, the medial supracondylar ridge of the femur, or from various other parts. The tendon of insertion may be attached to the Iliotibial band and to retinacular fibers of the lateral joint capsule.''The Adult Knee, vol. 1'', ed. Callaghan
p. 70
/ref> A slip may pass to the gastrocnemius.

Innervation

It is a composite muscle as the short head of the biceps femoris develops in the flexor compartment of the thigh and is thus innervated by common fibular branch of the

(L5, S1), while the long head is innervated by the tibial branch of the sciatic nerve (L5, S1).

Blood supply

The muscle's vascular supply is derived from the

anastomoses An anastomosis (, : anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf#Veins, leaf veins, or streams. Such a connection may be ...

of several arteries: the perforating branches of the profunda femoris artery, the inferior gluteal artery, and the popliteal artery.

Function

Both heads of the biceps femoris perform knee flexion.Origin, insertion and nerve supply of the muscle
at Loyola University Chicago Stritch School of Medicine Since the long head originates in the pelvis it is involved in hip extension. The long head of the biceps femoris is a weaker knee flexor when the hip is extended (because of active insufficiency). For the same reason the long head is a weaker hip extender when the knee is flexed. When the knee is semi-flexed, the biceps femoris in consequence of its oblique direction rotates the leg slightly outward.

Clinical significance

Avulsion of the biceps femoris tendon is common in sports that require explosive bending of the knee as seen in sprinting.

References

External links

UWash
- long head
UWash
- short head * * {{Authority control Knee flexors Thigh muscles Posterior compartment of thigh Muscles of the lower limb Hamstring