Biceps femoris muscle

Biceps femoris
Biceps femoris
	Lateral aspect of right leg. Biceps femoris muscle long head labeled
	Same picture with the visible part of the short head beneath the long head labeled
Details
Origin	tuberosity of the ischium, linea aspera, femur
Insertion	the head of the fibula which articulates with the back of the lateral tibial condyle
Artery	inferior gluteal artery, perforating arteries, popliteal artery
Nerve	long head: tibial nerve; short head: common peroneal nerve
Actions	flexes knee joint, laterally rotates knee joint (when knee is flexed), extends hip joint (long head only)
Antagonist	Quadriceps muscle
Identifiers
Latin	musculus biceps femoris
TA98	A04.7.02.032
TA2	2638
FMA	22356
	Anatomical terms of muscle [edit on Wikidata]

The biceps femoris is a muscle of the posterior (the back) thigh. As its name implies, it has two parts, one of which (the long head) forms part of the hamstrings muscle group.

Anatomy

Origin and insertion

It has two heads of origin;

one, the long head, arises from the lower and inner impression on the back part of the tuberosity of the ischium, by a tendon common to it and the semitendinosus, and from the lower part of the sacrotuberous ligament;^[1]
the other, the short head, arises from the lateral lip of the linea aspera, between the adductor magnus 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.^[1]

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; this aponeurosis becomes gradually contracted into a tendon, which is inserted into the lateral side of the head of the fibula, and by a small slip into the lateral condyle of the tibia.^[1]

At its insertion the tendon divides into two portions, which embrace the fibular collateral ligament of the knee-joint.^[1]

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.^[1]

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.^[1]

A slip may pass to the gastrocnemius.^[1]

Action

Both heads of the biceps femoris perform knee flexion.^[2]

Since the long head originates in the pelvis it is also involved in hip extension.^[2] 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.

Innervation

The short head of the biceps femoris develops in the flexor compartment of the thigh and is thus innervated by common peroneal branch of the sciatic nerve (L5, S2), while the long head is innervated by the tibial branch of the sciatic nerve (L5, S2).^[3]