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 fibers extend downward from the knee to the middle of the outer condyle of the femur (upper leg bone). The tendon of the semimembranosus muscle, along with the semitendinosus and gracilis, form the inner hamstring.
