The bones of the skeleton are designed for specific functions and come in four types:

1. Long bones made up of a hollow cylindrical shaft of compact (solid and dense) bone with cancellous (spongy) bone at the ends, e.g. the femur.

2. Short bones made up of small cube-shaped blocks of cancellous bone covered in a thin layer of compact bone, e.g. the carpels of the hand.

3. Flat bones are thin structures made up of two layers of compact bone with cancellous bone in between, e.g. the ribs and cranium.

4. Irregular bones are bones that do not fit into any other classifications, e.g. some bones of the cranium, the vertebrae, and the patella. In terms of structure they are like short bones.

Long, short, flat and irregular bones are all formed of the two main types of osseous tissue, cancellous (spongy) and compact (dense) bone. Cancellous bone is formed from trabeculae or 'small beams' that link together forming a network. This matrix structure has spaces in it that are filled with bone marrow. Compact bone is quite the opposite to this and is made of a hard, dense tissue that has a smooth exterior.