The biceps femoris () is a muscle of the

thigh In human 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 ...

located to the posterior, or back. As its name implies, it has two parts, one of which (the long head) forms part of the

hamstring In human anatomy, a hamstring () is any one of the three posterior thigh muscles in between the hip and the knee (from medial to lateral: semimembranosus, semitendinosus and biceps femoris). The hamstrings are susceptible to injury. In quadrupe ...

s muscle group.

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 swelling posteriorly on the superior ramus of the ischium. It marks ...

. This is a common tendon origin with the semitendinosus muscle, and from the lower part of the sacrotuberous ligament. *the ''short head'', arises from the lateral lip of the

linea aspera The linea aspera ( la, rough line) 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 ...

, between the

adductor magnus Adductor may refer to: * One of the anatomical terms of motion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminolo ...

and

vastus lateralis The vastus lateralis (), also called the vastus externus, is the largest and most powerful part of the quadriceps femoris, a muscle in the thigh. Together with other muscles of the quadriceps group, it serves to extend the knee joint, moving the ...

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 belly, which passes obliquely downward and lateralward across the sciatic nerve to end in an aponeurosis 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 The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity i ...

. There is a second small insertional attachment by a small tendon slip into the lateral condyle of the

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

. 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 h ...

. 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 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 swelling posteriorly on the superior ramus of the ischium. It marks th ...

, 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 The iliotibial tract or iliotibial band (ITB; also known as Maissiat's band or the IT band) is a longitudinal fibrous reinforcement of the fascia lata. The action of the muscles associated with the ITB (tensor fasciae latae and some fibers of glu ...

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 The gastrocnemius muscle (plural ''gastrocnemii'') is a superficial two-headed muscle that is in the back part of the lower leg of humans. It runs from its two heads just above the knee to the heel, a three joint muscle (knee, ankle and subtalar ...

Innervation

It is a

composite muscle Composite or hybrid muscles are those muscles which have more than one set of fibers but perform the same function and are usually supplied by different nerves for different set of fibers. Examples * Brachialis: Musculocutaneous nerve is motor an ...

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 sciatic nerve (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 (, plural 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, or streams. Such a connection may be norm ...

of several arteries: the perforating branches of the

profunda femoris artery The deep artery of the thigh, (profunda femoris artery or deep femoral artery) is a large branch of the femoral artery. It travels more deeply (posteriorly) than the rest of the femoral artery. Structure The deep artery of the thigh branches of ...

, the

inferior gluteal artery The inferior gluteal artery (sciatic artery), the smaller of the two terminal branches of the anterior trunk of the internal iliac artery, is distributed chiefly to the buttock and back of the thigh. It passes down on the sacral plexus of nerves ...

, and the

popliteal artery The popliteal artery is a deeply placed continuation of the femoral artery opening in the distal portion of the adductor magnus muscle. It courses through the popliteal fossa and ends at the lower border of the popliteus muscle, where it branche ...

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