HOW DOES THE BODY MOVE? 



369 



the body. Look at the bony skull which protects the 



brain, and notice how well it is fitted to do this. Observe 



in the accompanying diagram how the curved 



ribs are attached in back to the backbone 



and in front to the breastbone, thus forming 



a protection for the delicate lungs and other 



organs held in the cavity they surround. 



What Are Bones Made of? If you burn 

 one leg bone of a chicken in a hot fire, it can 

 be reduced to a little heap of white ashes, 

 largely lime. If the other leg bone is 

 placed for a few days in a 10 per cent solu- 

 tion of hydrochloric acid, the mineral 

 matter will be dissolved out so that the 

 bone can be tied into a knot. Thus we 

 see bone is made of animal matter as well 

 as mineral. The bones of young people 

 are growing and contain relatively more 

 animal matter than do the bones of older 

 people. A broken bone, therefore, is much 

 more serious in an older person. Do you 

 see why? Live bones are surrounded with 

 a delicate covering of living matter, through 

 which they absorb nourishment. Damage 

 to this part of the bone is serious because 

 it cuts off the food supply from the bone. 



Bones and Muscles. How we admire an athlete ! And 

 how most of us enjoy playing games or swimming or 

 hiking. Have you ever thought why the machine we call 

 the body can do these things so well ? Let us look at the 

 diagram on page 368. The skeleton in a general way 

 seems to have two purposes : one, protection ; the other, 

 to aid in movement. Move your own arm and you will 

 see that the long bones are jointed. Now compare with 

 the diagram and you will find the structures we call 

 H. & w. sci. i 25 



Does the skele- 

 ton give shape to 

 the body? What 

 other functions 

 has it ? 



