The shaft of a long bone is called the diaphysis. The narrow shaft transitions into regions called metaphyses, which terminate in broad, substantial areas of bone called epiphyses. These epiphyses form joints with other bones.
The shaft is made up of compact bone that is covered with a strong membrane called the periosteum. Down the center of the shaft is a hollow that contains bone marrow.
Long bones facilitate skeletal mobility and include the femur, fibula, tibia, ulna, radius and humerus. The phalanges and clavicles are also classified as long bones, even though they are smaller in comparison to the limbs.