CHAPTER III 

 BONES, JOINTS AND LIGAMENTS 



Purpose of the skeleton. The purpose of a skeleton 

 is to maintain the shape of the body in spite of its weight 

 and the pull of its muscles. To serve this purpose, the 

 bones must be rigid, strong and light. Their strength 

 and rigidity they owe to the material of which they are 

 made. Their lightness in proportion to their strength 

 is due to the fact that they are hollow. 1 



Composition of bone. Bones contain about sixteen 

 per cent of. an animal substance called collagen, which 



incellated bone Periosteum of shaft 

 'Epiphyseal line 

 iphysis 

 Articular cartilage 



FIG. 20. Longitudinal section of long bone (tibia), showing structure. 



when boiled becomes gelatine; thirty-four per cent of 

 earthy matter, chiefly salts of lime ; and the remaining 

 fifty per cent, water. To the collagen, the bone owes 

 its toughness ; to the salts of lime, its rigidity and hard- 

 ness. Although bone without moisture might possess the 

 advantage of increased lightness in proportion to its 



1 Hollow stems, like hollow bones, are found throughout nature, 

 as in grass, grains, reeds and bamboo. In manufactures, man has 

 imitated this, as in the bicycle frame, which combines great 

 strength and lightness. 



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