The tibia is categorized as a long bone and is as such composed of a diaphysis and two epiphyses. The diaphysis is the midsection of the tibia, also known as the shaft or body. While the epiphyses are the two rounded extremities of the bone; an upper (also known as superior or proximal) closest to the thigh and a lower (also known as inferior or distal) closest to the foot. The tibia is most contracted in the lower third and the distal extremity is smaller than the proximal.