The semimembranosus muscle is one of the hamstring muscles. It flexes the lower leg at the knee joint and rotates it in. It consists of a fleshy muscle belly with a tendon at each end. The muscle fibres originate from the tuberosity of the ischium and extend downward from the knee to insert in the middle of the outer condyle of the femur (upper leg bone) and the medial condyle of the tibia (lower leg bone). It is innervated by the tibial nerve and supplied by the profunda femoris. The tendon of the semimembranosus muscle, along with the semitendinosus and gracilis, form the inner hamstring. Research Semimembranosus Muscle