CHAPTER VI 



THE BONES OF OUR BODY ARE LIVING LEVERS. THE SKULL, 

 BESIDES CONTAINING THE BRAIN, SERVES AS A LEVER 

 OF THE FIRST ORDER 



In all the foregoing chapters we have been considering 

 only the muscular engines of the human machine, 

 counting them over and comparing their construction and 

 their mechanism with those of the internal-combustion 

 engine of a motor cycle. But of the levers or crank- 

 pins through which muscular engines exert their power 

 we have said nothing hitherto. Nor shall we get any 

 help by now spending time on the levers of a motor cycle. 

 We have already confessed that they are arranged in a 

 way which is quite different from that which we find in 

 the human machine (page 14). In the motor cycle all the 

 levers are of that complex kind which are called wheels, 

 and the joints at which these levers work are also circular, 

 for the joints of a motor cycle are the surfaces between 

 the axle and the bushes which have to be kept constantly 

 oiled. No, we freely admit that the systems of levers in 

 the human machine are quite unlike those of a motor 

 cycle. They are more simple, and it is easy to find in 

 our bodies examples of all the three orders of levers. The 

 joints at which bony levers meet and move on each other 

 are very different from those we find in motor cycles. In- 

 deed, I must confess they are not nearly so simple. And, 

 lastly, I must not forget to mention another difference. 

 These levers we are going to study are living — at least, 

 are so densely inhabited by myriads of minute bone 

 builders that we must speak of them as living. I want 



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