Note the following features in this cancellous bone: the bony trabeculae, osteocytes in the trabeculae (arrowhead), osteoblasts (tip of arrow) on all surfaces of the trabeculae, the connective tissue filling the spaces, and the centrally located blood vessels (base of arrow). The connective tissue space is gradually filled in by the addition of new layers of bone to the inside of the trabeculae. However, the CENTRALLY LOCATED BLOOD VESSELS REMAINS. The structural unit of bone thus formed is termed an OSTEON or HAVERSIAN SYSTEM. The central canal is lined by endosteum containing blood vessels (and nerves) is called the OSTEONAL (HAVERSIAN) CANAL. The circular layers of bone around the canal are termed OSTEONAL (HAVERSIAN) LAMELLAE. The lamellae contain embedded osteocytes which are also arranged in a circular fashion around the canal. The embedded osteocytes receive their nutrition by tissue fluid leaving the central vessel and diffusing through canaliculi to each and every osteocyte.
The bar is upon the periosteum whereas the tip of the arrow is at endosteum.
