This light micrograph shows a cross section of compact bone, magnified 540 times. This type of bone is dense and hard. It makes up the walls of the skeleton's long bones - the thigh bone, or femur, for example. Compact bone consists of numerous cylinders, each composed of concentric layers of bone around a central canal, which carries blood vessels, lymph vessels and nerves. The cross section also reveals black spots, which are spaces containing the cells that maintain the bony matrix.