This image shows a model of compact bone, which contains functional units called osteons (Haversian systems). Haversian canals that run parallel to the long axis of the bone are joined together and connected with the bone marrow and periosteum by transverse Volkmann's canals. The periosteum (which is richly supplied with nerve fibers, blood vessels and lymphatic vessels) is a double layered membrane that covers the outer surface of the bone. The inner layer of the periosteum is made up of undifferentiated osteogenic cells, which can give rise to osteoblasts that form new bone, or they may become fibroblasts that lay down new connective tissue cells that form the fibrous outer layer of the periosteum. The periosteum is secured to the underlying bone by
collagenous Sharpey´s fibers that extend from the fibrous layer into the bone matrix. In addition to the concentric lamellae found within each Haversian system, interstitial lamellae may appear between the systems. In long bones circumferential lamellae extend completely around the outer surface and inner surface of the bone.