Compact bones have many layers that contain soft materials, such as tissues and cells, and hard outer shells. Compact bones are found in all parts of the body, including the limbs, spinal cord and skull. These bones are found in all four types of bones: long bones, short bones, flat bones and irregular bones.
Compact bones come in many lengths, sizes and shapes but share a basic composition. In the form of long bones, they have elongated, bell-shaped knobs at the end of each bone and a center region that connects the two end points. In the form of short bones, they are long and straight, much like a needle, and lack the swollen ends found on long bones. Compact flat bones look much like the blade of a knife: thin and smooth. Lastly, these bones occur as irregular bones such as sesamoid bones, which are circles of bones surrounded by tendons. Compact bones consist of soft center regions filled with tissues, cells (called osteoblasts), arteries and nerves. As suppliers and transporters of nutrients and materials, they serve as the central locations of life and activity within bones, much like cities do for humans. Surrounding these bones is a thin membrane called periosteum, which is made of dense connective tissue filled with collagenous fibers and a variety of cells.