CHAPTER XXXII 

 THE SKELETON AND THE MUSCLES 



The skeleton has for its general function the support 

 and protection of the organs of the body. If we were to 

 be deprived of our framework of bones we should collapse 

 at once into an inert and flabby mass of flesh. What 

 gives the bones the rigidity necessary for their functions 

 is the presence of mineral constituents consisting chiefly 

 of phosphate and carbonate of lime. These substances 

 may be dissolved out of bone by means of nitric acid 

 leaving a tough, gristly counterpart which may be 

 readily bent or even tied in a knot. On the other hand, 

 when bones are burned the tough animal matter is con- 

 sumed, leaving only the mineral salts with which it was 

 impregnated. 



A part of our skeleton is formed of tough animal matter 

 called cartilage which has but a . very small quantity of 

 mineral salts. Cartilage occurs when bones are growing 

 and where flexibility is required, as at the ends of the ribs. 

 At the joints the bones are bound together by very tough 

 and inelastic bands of connective tissue called ligaments. 

 In many cases the bones are joined so as to permit freedom 

 of movement in one or more directions. We have the so- 

 called hinge joints at the knee, and elbow, permitting a 

 back and forth motion, and ball-and-socket joints at the 

 hip and shoulder, enabling the limb to move in any direc- 

 tion. Movable joints are enclosed in a synovial membrane 

 whose secretion, the synovial fluid, serves to lubricate the 

 surfaces of the united bones. Many of the long bones like 



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