Osteon

Osteons (also called Haversian system in honor of Clopton Havers ) are predominant structures found in some lamellar or compact bone. Osteons run parallel to the long axis of bones. In the center of the osteon is a central canal, sometimes called osteon or Haversian canal. The central canal is surrounded by concentric layers of matrix called lamellae. Collagen fibers in a lamellae run parallel to each other but the orientation of collagen fibers across separate lamellae is oblique. The fiber density is also lower at the border between adjacent lamellae, which accounts for the distinctive appearance of an osteon. Osteocytes are found between concentric lamellae and connected to each other and the central canal by cytoplasmic processes called canaliculi. This network permits the exchange of nutrients and metabolic waste. Osteons are separated from each other by cement lines. Collagen fibers and canaliculi do not cross cement lines. The space between separate osteons is occupied by interstitial lamellae, which were formed by pre-existing osteons that have since been reabsorbed. Osteons are connected to each other and the periosteum by oblique channels called Volkmann's canal.