Bones may be classified according to shape. This classification is of special interest to the X-ray specialist.

Long Bones

These are long, usually cylindrical, shafts with two expanded extremities. Long bones are radiographed lengthwise on the film. The humerus

Short Bones

These bones are short, usually cylindrical shafts, with two expanded extremities. They usually occur in groups, like the metacarpals of the hand. Generally, short bones are radiographed crosswise on the film.

Flat Bones

Flat bones consist of two plates of hard, bony substance with a layer of spongy, red marrow in between. In the adult, the red marrow is the normal site for the production of granulocytes (granular leukocytes) and erythrocytes. The scapula is an example of a flat bone.

Irregular Bones

These are bones whose size and shape are modified by their function and position. The vertebrae are examples of irregular bones.

Sesamoid Bones

Sesamoid bones are small bones embedded in tendons that pass over the joints. In addition to lessening friction, they modify pressure and help to protect ligaments and tendons. The patella (kneecap) of the knee joint  is an example of a sesamoid bone. Sesamoid bones are also situated within the palm of the hand and the plantar surface of the foot.

Supernumerary Bones

These are “extra” bones of the skeletal system, such as an extra vertebra or rib, plus most sesamoid bones.

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