Bone tissue. Darkfield illuminated light micrograph of a section through mature bone tissue, showing the concentric patterns of osteocyte cells within osteons. Osteons, or Haversian systems, are branching cylinders of concentric layers of bone matrix and their embedded cells (osteocytes). The centre of the osteon contains a Haversian canal, through which capillaries supply nutrients and provide for the addition to, or removal of, calcium from the tissue. The osteocytes have many long thin cytoplasmic extensions that permeate via narrow channels or canaliculi into the surrounding bone matrix tissue. Magnification: x30 when printed 10 centimetres wide.