Compact bone. Light micrograph of a cross-section through a femur, the long bone of the upper leg. The shaft of the femur is made of compact bone, a dense form of bone in which the bone units (lamellae) are tightly organised. Some, known as circumferential lamellae, form layers on the outer and inner surfaces of the bone. However, most of the lamellae are arranged in units called osteons or Haversian systems (circular), which have a central cavity containing blood vessels. The spaces between the osteons are filled with interstitial lamellae. Magnification: x23 when printed 10cm wide.