Editing Bone (section)

===Cortex===
[[File:Illu compact spongy bone.jpg|thumb|Cross-section details of a long bone]]

The hard outer layer of bones is composed of '''cortical bone''', which is also called '''compact bone''' as it is much denser than cancellous bone. It forms the hard exterior (cortex) of bones. The cortical bone gives bone its smooth, white, and solid appearance, and accounts for 80% of the total bone mass of an adult [[human skeleton]].<ref>{{Cite web|title=Structure of Bone|publisher=CK12-Foundation|url=https://flexbooks.ck12.org/cbook/ck-12-college-human-biology-flexbook-2.0/section/13.4/primary/lesson/structure-of-bone-chumbio|website=flexbooks.ck12.org|access-date=2020-05-28}}</ref> It facilitates bone's main functions—to support the whole body, to protect organs, to provide [[lever]]s for movement, and to store and release chemical elements, mainly calcium. It consists of multiple microscopic columns, each called an [[osteon]] or Haversian system. Each column is multiple layers of [[osteoblast]]s and [[osteocyte]]s around a central canal called the [[Haversian canal|osteonic canal]]. [[Volkmann's canal]]s at right angles connect the osteons together. The columns are metabolically active, and as bone is reabsorbed and created the nature and location of the cells within the osteon will change. Cortical bone is covered by a [[periosteum]] on its outer surface, and an [[endosteum]] on its inner surface. The endosteum is the boundary between the cortical bone and the cancellous bone.{{sfn|Young|2006|p=192}} The primary anatomical and functional unit of cortical bone is the [[osteon]].