[TA] deep hamstring muscle of posterior (flexor) compartment of thigh; origin, tuberosity of ischium; insertion, medial condyle of tibia and by membrane to tibial collateral ligament of knee joint, popliteal fascia, and via its reflected tendon of insertion (oblique popiteal ligament) lateral condyle of femur; action, flexes knee and rotates leg medially when knee is flexed; and contributes to the stability of extended knee by making capsule of knee joint tense; nerve supply, tibial. SYN: musculus semimembranosus [TA].