Light microscopy of a thick (approx. 50 m) unstained section of mature bone. The circular and elliptical structures are osteons (also called Haversian systems) consisting of osteocytes embedded in concentric rings of bone matrix. Each osteon is like a cylinder, often branched and usually oriented parallel to the greatest forces placed upon a particular location within a bone. In the centre of osteons is a tunnel-type space or canal with blood vessels; canals pass between osteons where they are called Volmann's canals. These are in continuity with external blood vessels supplying the bone. Magnification x35 when printed at 10cm.