This image shows the major muscles of the ventral surface of the frog thigh. The sartorius (1) is a long, strap-shaped muscle that covers the anterior surface of the thigh. It originates on the pubis, inserts on the tibiofibula and acts to flex the thigh and shank. The sartorius (2) of the right leg is shown with its distal end cut and deflected to make it more visible. The adductor longus (3), which originates on the pubis and inserts on the femur, is a thin, strap-shaped muscle beneath the sartorius. Note: This muscle of the right leg has also been cut at its distal end and deflected to make it more visible. As the name implies, the adductor longus functions to adduct the thigh. The adductor magnus (4), which also adducts the thigh, is a large muscle seen as a triangle near the groin when the sartorius is in place. The muscle originates on the ischium and pubis and inserts on the femur. The semitendinosus (5) is a deep muscle with two heads that lies under and between the gracilis major and adductor magnus. The muscle originates on the ischium, inserts on the tibiofibula. The semitendinosus extends and adducts the thigh and flexes the knee. The gracilis major (6) is a large muscle that partly covers adductor magnus. It originates on the pubis, inserts on the tibiofibula and acts to extend the thigh and flex the shank.