Coloured scanning electron micrograph (SEM) of an osteocyte (brown) in compact, or cortical, bone. Compact bone forms a bone's dense outer layer. Osteocytes, cells involved in bone remodelling, are found in small spaces known as lacunae. Cortical bone accounts for 80 per cent of the total bone mass of an adult human skeleton. The picture was created as part of a cooperation with Quintessenz Publishing. Magnification: x3,000 when printed at 15cm wide.