In early and late foetal life, bone is composed exclusively of trabecules of primary bone, also referred to as woven bone (black). The osteoblasts are shown as dots at the periphery of the superficial trabecules. Larger osteoclasts are shown on the endosteal surface. During childhood, concentric bone lamellae are formed in spaces present between trabecules of primary (woven) bone. This primary bone progressively disappears through the dissolving action of osteoclasts. In adults, compact bone is composed almost exclusively of lamellar bone, which is continually restructured by dissolution and replacement by osteon reconstruction as illustrated in figures 8.14 and 8.15.