Bone tissue, light micrograph. Unstained thick section of adult bone showing osteons in circular and elliptical profiles. Also known as Haversian systems, osteons are comprised of mineralized bone matrix organised into concentric shells surrounding a central vascular canal seen here as empty spaces. The cells of osteons are osteocytes seen as black nuclei with many fine cytoplasmic processes extending into the matrix. Up to several centimetres in length with branching and 250 micrometres in diameter, osteons give bone its strength and provide for exchange of calcium and phosphate between the bone matrix and blood vessels. Magnification: x85 when width printed at 10cm.