Final answer:
The gracilis muscle inserts at the medial surface of the tibial shaft, aiding in adducting the femur at the hip and flexing the leg at the knee.
Step-by-step explanation:
The insertion site of the gracilis muscle is the tibia, specifically at the medial surface of the tibial shaft. It is one of the muscles in the medial compartment of the thigh that are responsible for adducting the femur at the hip. The gracilis muscle, which is a thin, strap-like muscle, also assists in flexing the leg at the knee. It is not associated with the femur, ilium, or the iliotibial (I.T.) band, but rather inserts onto the tibia, contributing to the movement of the lower leg.