Bone ‒ Section

**Compact bone** is the denser and stronger of the two types of bone tissue. It is located beneath the periosteum and in the diaphyses of long bones, where it provides essential support and protection. The microscopic structural unit of compact bone is the osteon, or Haversian system, which is composed of concentric rings of calcified matrix called lamellae (singular: lamella). Running down the center of each osteon is the **central canal, or Haversian canal**, which contains blood vessels, nerves and lymphatic vessels. These vessels and nerves branch off at right angles through a perforating canal, also known as Volkmann's canals, to extend to the periosteum and endosteum. Like compact bone, **spongy bone**, also called cancellous bone, contains osteocytes housed in lacunae; however, these cells are not arranged in concentric circles. Instead, the lacunae and osteocytes are located in a lattice-like network of matrix spikes called trabeculae (singular: trabecula). Although the trabeculae may appear random, each forms along lines of stress to provide strength to the bone. The trabeculated network balances the dense, heavy compact bone by making bones lighter, allowing easier movement by the muscles. In addition, the spaces within some spongy bones contain red marrow, protected by the trabeculae, where hematopoiesis (blood cell formation) occurs. *LICENSES AND ATTRIBUTIONS CC licensed content, Shared previously, Donna Browne, Skeletal System Module 4: Bone Structure, Authored by: OpenStax College. License: CC BY: Attribution. License Terms: Download for free at http://cnx.org/contents/5Ofth9yh@2/Skeletal-System-Module-4--Bone*