In compact bone, the concentric rings of matrix laid down around a central canal form a structure called

Explanation

A Haversian system, or osteon, is the cylindrical unit of compact bone: rings of hard matrix around a canal carrying a blood vessel and a nerve, with osteocytes trapped in small spaces called lacunae between the rings. The lacuna is therefore part of the system rather than the system itself. The periosteum is the fibrous sheath on the outside of the bone.