The largest bone in the body, and only bone in the upper leg, is the femur. The femur’s head creates the ball-and-socket hip joint and the base of the femur connects to the knee. The major muscles in the upper leg are the hamstrings at the back of the thigh and the quadriceps in the front of the thigh.
The lower leg has two bones, the tibia, which meets the femur at the knee, and the fibula. The tibia supports most of the body weight and is an important part of both the knee and ankle joints. The lower leg contains many muscles to help raise the leg and to facilitate foot movements. The Achilles tendon connects the calf muscles to the heel bone and is used when walking, running, and jumping.