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Semimembranosus muscle
Muscles of the gluteal and posterior femoral regions. Semimembranosus labeled at bottom left.
Semimembranosus labeled at bottom right.
Latin	musculus semimembranosus
Gray's	subject #128 479
Origin:	Ischial tuberosity
Insertion:	Medial surface of tibia
Artery:	profunda femoris, gluteal artery
Nerve:	sciatic nerve
Action:	Hip extension, Knee flexion
Antagonist:	Quadriceps muscle
Dorlands/Elsevier	m_22/12550673

The semimembranosus is a muscle in the back of the thigh. It is the most medial of the three hamstring muscles.

Contents 1 Structure 2 Innervation 3 Actions 4 Variations 5 Additional images 6 See also 7 External links

The semimembranosus, so called from its membranous tendon of origin, is situated at the back and medial side of the thigh.

It arises by a thick tendon from the upper and outer impression on the tuberosity of the ischium, above and lateral to the biceps femoris and semitendinosus.

The tendon of origin expands into an aponeurosis, which covers the upper part of the anterior surface of the muscle; from this aponeurosis muscular fibers arise, and converge to another aponeurosis which covers the lower part of the posterior surface of the muscle and contracts into the tendon of insertion.

It is inserted mainly into the horizontal groove on the posterior medial aspect of the medial condyle of the tibia.

The tendon of insertion gives off certain fibrous expansions: one, of considerable size, passes upward and lateralward to be inserted into the back part of the lateral condyle of the femur, forming part of the oblique popliteal ligament of the knee-joint; a second is continued downward to the fascia which covers the Popliteus muscle; while a few fibers join the tibial collateral ligament of the joint and the fascia of the leg.

The muscle overlaps the upper part of the popliteal vessels.

The semimembranosus is innervated by the tibial part of the sciatic nerve.

The semimembranosus helps to extend (straighten) the hip joint and flex (bend) the knee joint. It also helps medially rotate the knee.

It may be reduced or absent, or double, arising mainly from the sacrotuberous ligament and giving a slip to the femur or adductor magnus.

Right hip bone. External surface.

Bones of the right leg. Posterior surface.

The popliteal, posterior tibial, and peroneal arteries.

Back of left lower extremity.

• Semitendinosus
• Biceps femoris

• LUC semm
• SUNY Labs 14:st-0408
• SUNY Figs 14:01-07 - "Muscles (hamstrings) of the posterior compartment of the thigh."
• SUNY Figs 14:02-06 - "Muscles that form the superficial boundaries of the popliteal fossa."
• Anatomy at Dartmouth knee/surface/surface4
• PTCentral

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.

v • d • e List of muscles of lower limbs
ILIAC REGION/ILIOPSOAS	psoas major/psoas minor - iliacus
BUTTOCKS	gluteals: (maximus, medius, minimus) - tensor fasciae latae lateral rotator group: piriformis - obturator externus/obturator internus - inferior gemellus/superior gemellus - quadratus femoris
THIGH	anterior compartment: sartorius - quadriceps (rectus femoris, vastus lateralis, vastus intermedius, vastus medialis) - articularis genu posterior compartment/hamstring: biceps femoris - semitendinosus, semimembranosus medial compartment/adductor: gracilis - pectineus - adductor brevis - adductor longus - adductor magnus
LEG	anterior compartment: tibialis anterior - extensor hallucis longus - extensor digitorum longus - fibularis tertius posterior compartment: superficial - calf/triceps surae (gastrocnemius, soleus) - plantaris - deep - popliteus - tarsal tunnel (flexor hallucis longus, flexor digitorum longus, tibialis posterior) lateral compartment: fibularis muscles (longus, brevis)
FOOT	dorsal - extensor digitorum brevis - extensor hallucis brevis plantar - 1st layer (abductor hallucis, flexor digitorum brevis, abductor digiti minimi) - 2nd layer (quadratus plantae, lumbrical muscle) - 3rd layer (flexor hallucis brevis, adductor hallucis - flexor digiti minimi brevis) - 4th layer (dorsal interossei, plantar interossei)