Final answer:
The biceps femoris is the only muscle in the hamstring group that inserts on the lateral part of the tibia, with its two heads allowing for knee flexion and lateral leg rotation.
Step-by-step explanation:
The hamstring group in the posterior compartment of the thigh includes three muscles: biceps femoris, semitendinosus, and semimembranosus.
These muscles primarily serve to flex the knee and extend the hip. Among them, it is the biceps femoris that is unique in its insertion onto the lateral part of the tibia, distinguishing it from the other hamstring muscles that insert medially on the tibia.
The biceps femoris has a long head, which originates from the ischial tuberosity, and a short head, which originates from the femur. Both heads converge to insert onto the head of the fibula and the lateral aspect of the tibia. This lateral insertion allows the biceps femoris not only to flex the knee but also to assist in the lateral rotation of the leg when the knee is bent.