semitendinosus /sem′iten′dinō″səs/ [L, semi + tendere, to stretch] , one of three posterior femoral muscles of the thigh, remarkable for the great length of the tendon of insertion. It is a fusiform muscle located in the posterior and medial part of the thigh, arising from the tuberosity of the ischium. It ends just distal to the middle of the thigh in a long round tendon that crosses the semimembranosus and curves around the medial condyle of the tibia and inserts into the medial surface of the tibia. It functions to flex the leg, to rotate it medially after flexion, and to extend the thigh. Compare biceps femoris, hamstring muscle, semimembranosus.
