Semimembranosus

Summary

Origins

• Superolateral facet of the ischial tuberosity on the pelvis

Insertions

• Posterior medial condyle of the tibia
• Reflected expansion to the popliteus fascia and oblique popliteal ligament

Actions

• Extends the hip
• Flexes the knee
• Medially rotates the leg when the knee is flexed
• Tenses the oblique popliteal ligament

The semimembranosus sits beneath the slender semitendinosus. It is a broad hamstring that rises from the ischial tuberosity of the pelvis. Its upper fibers blend with the nearby biceps femoris tendon before sweeping toward the back of the knee.

Near the knee the muscle splits into several slips. One anchors on the back and inner edge of the tibia. Another reflects across the joint to reinforce the oblique popliteal ligament. A thin expansion reaches the medial meniscus. Together they let the muscle extend the hip, bend the knee, and turn the tibia inward when the knee is flexed.

Because it helps frame the medial wall of the popliteal fossa, the semitendinosus that drapes over it casts a soft ridge that marks the hollow behind the knee. Follow this sheet-like belly when you draw seated figures or athletes pushing off the planted leg.

References

• Wikipedia