BONES 163 



By sitting, standing^ and walking erect, we can make 

 our backbones straight and our chests full. A soldier is 

 straight because he has had to keep his back straight until 

 it grew so. 



SUMMARY 



I.. Two hundred bones form a strong frame for the body. 

 Some are long and some are flat. 



2. Bones are made of living cells, in which lime is mixed 



to give them stiffness. 



3. The union of two bones is a joint. Some, as those of 



the head, cannot be moved. They allow the bones 

 to spring a little instead of breaking, when they are 

 hit or pressed. 



4. The bones of the spine can move a little, for they are 



joined together by pads like rubber cushions. 



5. In the arms and legs the bones fit together by means 



of rounded surfaces. They are covered with car- 

 tilage and are held in place by loose ligaments. 



6. Joints are oiled by a fluid like the white of an egg, 



called the synovial fluid. 



7. Most joints move back and forth like a hinge. The 



shoulder and hip can be moved in any direction. 



8. The cells of a broken bone soon fill in the gap with 



the new cells, and then deposit lime in the new 

 part. This heals the bone. 



9. In sprains, and when bones are out of joint, the liga- 



ments are torn and require a long time to heal. 

 10. When the body keeps an improper position for days 

 at a time, it will grow into that position. 



