190 THE HUMAN MACHINE 



where muscles might be attached. In each case seek a place for 

 attachment for the other end of the muscle. 



Conclusion. — 1. Write a statement giving "three general uses of 

 the human skeleton. Take a special bone or bones to illustrate 

 each use. 



2. Compare the skeleton with the figure on page 268, Civic 

 Biology. Make a drawing to identify the principal bones. 



Problem, 167 : To find the relation of muscles to tones in the 

 human body. 



Method. — Using the diagrams in your Civic Biology, page 269, 

 work out the different classes of levers. 



Observations. — • In the human body which class of lever is 

 represented when we raise a weight in the hand ? What kind of 

 lever do we use when we rise on the toes? What kind of lever 

 do we use when we nod the head? 



Conclusion. — 1. Prove that three classes of levers are present 

 in the human body. 



2. Find another example of each kind of lever in the human 

 body. 



Problem 168 : To study the joints of the human body. 



Materials. — Human skeleton. 



Method. — Study the following joints in the human skeleton: 

 arm at shoulder, knee, head on neck bones, bones of spinal 

 column. Move them in each case. 



Observations. — Is the joint hinge-like, ball and socket, gUding, 

 or rotary ? 



Conclusion. — 1. How many different kinds of joints can you 

 find in a skeleton? 



2. What are their specific uses? 



Problem 169: To get a preliminary survey of the internal 

 structure of the human body. 



Materials. — Manikin and charts showing organs of the human 

 body. 



Observations. — If we compare the human body to a machine, 

 then the bones and muscles are the framework. Within the body, 



