Chap. 7 TISSUES 117 



These salts are largely calcium phosphate and calcium carbonate. Two types 

 of structure are found in most bones, compact bone and latticed or spongy 



Fig. 7.10. The intervetebral disk or cushion be- 

 tween the vertebrae mainly composed of white 

 fibrous cartilage. A human vertebra seen from 

 above with part of the intervertebral disk adhering 

 to it. The outer side of the vertebra is down; in 

 life the hole contains the nerve cord. 1, rings of 

 fibers arranged in layers; 2, a small central body 

 of cartilage (nucleus pulposus). (Courtesy, 2"^'"' •5^ 

 Elements of Anatomy, ed. 11. New York, Long- 

 mans, Green & Co., 1915.) 



bone. The Haversian system is the unit of bony structure (Fig. 7.12). Its odd 

 name comes from that of Clapton Havers, an English anatomist, who de- 

 scribed the system in the 17th century. The unit is an irregularly cylindrical 

 structure with a central or Haversian canal containing nerves and blood 



Fig. 7.11. Bone cells in a thin section of human thigh bone (femur) with bone 

 cells and their processes highly magnified; the naturally colorless nuclei have been 

 deeply stained. The bone cell lies in a minute cavity (lacuna) with its living 

 processes extending into extremely fine canals (canaliculi) which branch out in all 

 directions through the intercellular substance often connecting with those of other 

 cells. Materials pass through these to and from the cells, ultimately to blood ves- 

 sels. (Courtesy, Nonidez and Windle: Textbook of Histology, ed. 2. New York, 

 McGraw-Hill Book Co., Inc., 1953.) 



