This image shows several of the major muscles on the dorsal surface of the frog thigh. The gluteus muscle (1), which originates on the ilium and inserts on the femur, rotates the thigh. The piriformis (2) is a small muscle located near the opening of the cloaca. The muscle originates on the urostyle, inserts on the femur and functions to extend and rotate the thigh. As the name indicates, the triceps femoris (3) is divided into three parts that originate and insert on different skeletal elements. All function, however, to flex the thigh and extend the shank. The semimembranosus (4), which originates on the ischium and pubis and inserts on the tibiofibula, extends the thigh and flexes the shank. The biceps femoris (5) found between the triceps femoris and semimembranosus originates on the ilium and inserts on the tibiofibula and femur. The biceps femoris extends and adducts the thigh and flexes the shank. Also shown on the image are the two major muscles of dorsal surface of the frog shank, the gastrocnemius (6) and peroneus (7).