Light micrograph of a unstained ground section of an adult long bone viewed in cross-section. The outer bone tissue is circumferential lamellae of multiple layers of bone matrix penetrated by blood vessels (small black circles). These vascular channels (Haversian canals) are also seen centrally in the bulk of the bone where circular osteons (Haversian systems) are seen. Some osteons are noted to be linked by branches of the Haversian canals. Parts of the innermost bone surface show longitudinal bone matrix lamellae and one vascular channel communicates with the empty core of the bone which in life contains bone marrow. Magnification: x1.6 when width printed at 10cm.