Chap. 9 PROTECTION, SUPPORT, AND MOVEMENT SKELETONS 145 



receives abundant nourishment through a network of blood vessels and is the 

 region that provides for increase in diameter in growing animals. 



Arteries enter and veins leave the bones in an oblique direction and are 



/synovial fluid 



-Articular cartilage 



^Jblood vessel 



yrOMPACT BONE 



<MARROW CAVITY 



'articular ugament 



Fig. 9.9. Structure of a long bone. Periosteum is the growth area. (Courtesy, 

 Rand: Chordate Anatomy. Philadelphia, The Blakiston Company, 1950.) 



connected by capillaries within them. The abundance of blood vessels in bone 

 emphasizes the fact that its cells are living, that metabolism goes on within 

 them as elsewhere, and that in them food and oxygen are expended, and heat, 

 energy, and waste are produced. Bone cells constantly take up organic and 

 inorganic substances from the blood and release such substances into it. 



A. Normal bone 



B. Soaked in HCL 

 (hydrochloric acid) 



C. Burned until collagen 

 fibers removed 



Fig. 9.10. A, normal bone. B, bone with calcium dissolved out after which it 

 can be bent and twisted. C, bone burned until the organic matter, cells and fibers, 

 are destroyed after which it is brittle. In a baby one year old the proportion of 

 calcium to animal matter is about as 1:8; at eighty years it is commonly about 

 8:11. 



