58 OSTEOLOGY 



that develop the osseous tissue by a process of cell 

 secretion. The genetic layer gives off bundles of fibers 

 which pierce the layers of bone at right angles and 

 bind them together. These are called Sharpey's fibers. 



Bone is classified as to its composition into cancellous 

 or spongy, compact or solid. 



Cancellous or Spongy Bone. This consists of spicules 

 forming a net-work similar to a sponge. These spicules 

 have a fibular structure, and between them are small 

 spaces called lacuna? (little lakes), which are filled 

 in the living state with osteoblasts. The cancellous 

 bone is found in the head of long bones, the centre 

 of flat bones, and around the medullary cavity. In 

 the centre of all long bones is a hollow cavity called 

 the medulla; it contains marrow. This medullary 

 cavity is lined with a fibrous layer of tissue called the 

 endosteum, which covers the net-work of spongy bone 

 surrounding the medullary canal. 



Compact or Solid Bone. This is the stronger of the 

 two varieties and forms the outer surface of the 

 long bones. It is arranged in layers called lamella?, 

 and can only be studied in section after preparation; 

 and when observed under the microscope it will present 

 a series of lamellae arranged around a central opening, 

 called the Haversian canal. These carry bloodvessels 

 in a longitudinal direction throughout the bone, 

 and communicate with each other. Between the 

 Haversian canals are lacunae lined with osteoblasts 

 they communicate with each other and the Haversian 

 canals by means of small canals called canaliculi. 

 Just beneath the periosteum the lamellae of bone are 

 derived from it. These layers have between them 

 lacunse with canaliculi connecting each other. The 

 most external lamella? present depressions termed 

 Howship's fovese or lacunas; these are filled with large 

 bone-destroying cells called osteoclasts. Haversian 

 canals are absent in the external lamellae beneath the 

 periosteum, but large canals are present, containing 

 blood from the periosteum Volkmann's canals. 



