The fibula is a long, thin bone that attaches next to and slightly below the tibia (shinbone). It carries only a little amount of body weight. The fibula provides lateral support for the lower leg and works as a tie rod to extend the ankle's range of motion, particularly lateral and medial foot rotation. The fibula is also important in determining the shape of the calf and heel. The bone has a relatively smooth surface except for several rugosities (little hills) on its upper side by which it fits into the head of the tibia. The human fibula is about 15 centimeters long. It lies behind the knee on the inner side of the leg. It forms a hook with which it attaches to two other bones in the lower leg, the talus and calcaneus. Its main function is to provide stability and balance to the ankle. The fibula is not included in the arm bone series because it does not meet the requirements to be classified as an arm bone. It does not reach far down the leg to touch the floor or even come close. Rather, it stays within the ankle region all the way up until it meets the heel bone (calcaneus). Furthermore, the fibula doesn't have a shoulder joint connection. It connects directly with the hip bone (ilium). Finally, the term "fibula" refers exclusively to the bone itself.