This muscle lies on the inner and back part of the radius or forearm, with which it is in contact.

Origin - From the inner surface of the internal condyle of the humerus-or upper-arm bone.

Insertion. - The tendon of insertion commencing some distance above the knee passes over a groove on the lower extremity of the radius, and is there surrounded by a synovial membrane; continuing downwards, it becomes inserted into the head of the inner small metacarpal bone.

Action. - To flex the knee-joint.