Compact bone, from human femur, transverse sections showing cross sections and arrangement of osteons and Haversian canals. Bone is made up of two types of tissue: the compact bone forms a shell around the spongy cancellous bone that makes up the marrow space in the centre. Compact bone provides strength and rigidity and is solid in appearance. It is composed of a layered matrix of organic substances and inorganic salts that form around an intricate network of vasculature called Haversian canals (named after British physician Clopton Havers), shown in this image in red. The Haversian canals surround blood vessels and nerve cells throughout the bone and together with the layers of compact bone, the canals form units called osteons. The tiny black spaces shown in this image are due to the loss of osteocyte cells (living bone cells) that have disappeared during processing leaving the holes within the bone. Air is often trapped inside these holes during specimen preparation, giving the cavities a dark appearance because of optical refraction.
