semitendinosus

noun

sem·​i·​ten·​di·​no·​sus ˌsem-ē-ˌten-də-ˈnō-səs 

plural semitendinosi -ˌsī 

: a fusiform muscle of the posterior and inner part of the thigh that arises from the ischial tuberosity along with the biceps femoris, that is inserted by a long round tendon which forms part of the inner hamstring into the inner surface of the upper part of the shaft of the tibia, and that acts to flex the leg and rotate it medially and to extend the thigh