360 APPLIED PHYSIOLOGY 



645. Microscopic appearance. Bone is composed of 

 branching connective tissue cells and fibers, which are 

 arranged in circles around minute tunnels called Haversian 

 canals. Each Haversian canal contains arteries, veins, 

 and nerves. Lime is mixed with the cells and canals like 

 starch among the fibers of linen, and imparts to them their 



a 



Thin slice of bone (x 200). 

 a bone cells. b Haversian canal, containing blood tubes and nerves. 



hardness and rigidity. Lime forms about two thirds of 

 the bone by weight. 



646. The periosteum carries arteries and nerves which 

 enter minute openings in the bone. During childhood, or 

 when a bone is diseased, the cells of its inner layer are 

 very active in reproducing themselves and in forming new 

 bone. Bone stripped of its periosteum is apt to die, 

 but when the bone dies the periosteum usually remains 

 alive and soon reproduces new bone. The periosteum 

 also affords an attachment for muscles. 



647. Cartilage. The bones of very young animals 

 contain little or no lime, but are soft and pliable. In this 



