Also called vastus internus, the vastus medialis is a long muscle located in the medial part of the thigh. It is one of the four muscles which make up the quadriceps femoris. The vastus medialis arises from a continuous line of attachment on the femur, which begins on the front and middle side on the intertrochanteric line of the femur, the linea aspera, the medial supracondylar line, the tendons of the adductor longus and the adductor magnus, and the medial intermuscular septum. The vastus medialis runs down to the lower anterior aspect of the thigh and inserts by an aponeurosis under the patella as part of the quadriceps femoris tendon and onto the medial condyle of the femur. An expansion of the aponeurosis passes to the capsule of the knee joint. The muscle functions in combination with other parts of the quadriceps femoris to extend the leg.