Light microscope section through human compact bone tissue. Compact bone or cortical bone forms the hard external layer of the bone that surrounds the medullary cavity and provides protection and strength to bones. Compact bone tissue consists of units called osteons or Haversian systems. The Haversian canal (osteonic canal) consists of the bone's blood vessels and nerve fibres. Osteons in compact bone tissue are aligned in the same direction along lines of stress and help the bone resist bending of fracturing