Long bones are "long": their length is superior to their width.

Section the bone of one of the arm: Long bone consist of a shaft (= diaphysis) and two expanded ends (= epiphysis, plural: epiphyses) that articulate with other bones.

- The diaphysis has a thick wall made of compact tissue surrounding a central cavity (= medullary cavity) containing yellow marrow (=fat).

- The epiphyses are covered by a thin layer of compact tissue. Their interior contains spongy bones and red marrow. On its outer surface, the articular portion of the epiphysis is coated with hyaline cartilage.

- Between epiphysis and diaphysis, there is the epiphyseal line. This is a left over of the epiphyseal plate, a thin plate of hyaline cartilage separating the epiphyses from the diaphysis. The epiphyseal plate exists only in young growing long bones and aloows them to grow in length.

The long bone is entirely covered by the periosteum except where the articular cartilage coats the epiphysis.

The endosteum covers the surface of the medullary cavity, the trabeculae of the spongy bone tissue and covers the wall of the various canals that pass through the compact bone.