Compact bone consists of closely packed osteons or Haversian systems. The osteon consists of a central canal called the osteonic (Haversian) canal, which is surrounded by concentric rings (lamellae) of matrix.
Between the rings of matrix, the bone cells (osteocytes) are located in spaces called lacunae. Small channels (canaliculi) radiate from the lacunae to the osteonic (haversian) canal to provide passageways through the hard matrix. In compact bone, the Haversian systems are packed tightly together to form what appears to be a solid mass.
The osteonic canals or the Haversian system contain blood vessels that are parallel to the long axis of the bone. These blood vessels interconnect, by way of perforating canals, with vessels on the surface of the bone.
Spongy (cancellous) bone is lighter and less dense than compact bone. Spongy bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow.
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