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 bone ...
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 quadrupeds, ...
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 th ...
. This is a common tendon origin with the
semitendinosus muscle
The semitendinosus () is a long superficial muscle in the 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.
Structure
The semitendinosus, r ...
, 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 lower ...
.
*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 asper ...
, between the
adductor magnus Adductor may refer to:
* One of the anatomical terms of motion
* Adductor muscle (disambiguation)
* Adductor canal
The adductor canal, also known as the subsartorial canal or Hunter’s canal, is an aponeurotic tunnel in the middle third of the th ...
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 l ...
extending up almost as high as the insertion of the
gluteus maximus
The gluteus maximus is the main extensor muscle of the hip. It is the largest and outermost of the three gluteal muscles and makes up a large part of the shape and appearance of each side of the hips. It is the single largest muscle in the human ...
, 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 means having a spindle-like shape that is wide in the middle and tapers at both ends. It is similar to the lemon-shape, but often implies a focal broadening of a structure that continues from one or both ends, such as an aneurysm on a b ...
belly, which passes obliquely downward and lateralward across the
sciatic nerve to end in an
aponeurosis
An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join musc ...
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 is ...
. 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
The lateral collateral ligament (LCL, long external lateral ligament or fibular collateral ligament) is a ligament located on the lateral (outer) side of the knee, and thus belongs to the extrinsic knee ligaments and posterolateral corner of the k ...
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 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
The inferior third of the medial border of the humerus is raised into a slight ridge, the medial supracondylar ridge (or medial supracondylar line), which becomes very prominent below; it presents an anterior lip for the origins of the Brachiali ...
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 normal ...
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 a ...
, 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 branches ...
.
Function
Both heads of the biceps femoris perform knee flexion.[Origin, insertion and nerve supply of the muscle](_blank)
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.
See also
Additional images
File:Gray235.png, Right hip bone. External surface.
File:Gray258.png, Bones of the right leg. Anterior surface.
File:Thigh cross section.svg, Cross-section through the middle of the thigh.
File:Gray1240.png, Muscles of the gluteal and posterior femoral regions.
File:Gray551.png, The popliteal, posterior tibial, and peroneal arteries.
File:Gray832.png, Nerves of the right lower extremity Posterior view.
File:Gray1239.png, Back of left lower extremity.
File:Slide1i.JPG, Biceps femoris
References
Further reading
*
*
*
External links
UWash
- long head
UWash
- short head
*
*
{{Authority control
Knee flexors
Thigh muscles
Posterior compartment of thigh
Muscles of the lower limb
Hamstring