PART II: MOTION, COORDINATION, 

 AND SENSATION 



CHAPTER XIV 

 THE SKELETON 



ONE necessary means of establishing proper relations 

 between the body and its surroundings is motion^ Not 

 only can the body move itself from place to place, but it 

 is able to move surrounding objects as well. In the pro- 

 duction of motion three important systems are employed 

 the muscular system, the nervous system, and a system 

 of mechanical devices which are found mainly in the 

 skeleton. The muscular system supplies the energy for 

 operating the mechanical devices, while the nervous system 

 controls the movements. 2 Although the skeleton serves 

 other purposes, such as giving shape to the body and pro- 

 tecting certain organs, its main use is that of an aid in the 

 production of motion. 



1 Review " Main Physiological Problems," page 21. 



2 In the production of motion in the body, as well as in the production of any 

 kind of purposeful motion outside of the body, three conditions must be fulfilled. 

 There is required, in the first place, a mechanical device or machine which is so 

 constructed as to produce a certain kind of motion. In the second place, energy 

 is needed to operate this device. And, finally, there must be some controlling 

 force, by means of which the motion is made to accomplish definite results. The 

 driving of a horse hitched to a wagon will illustrate these conditions. The wagon 

 is the mechanical device, the horse furnishes the energy, and the driver supplies 

 the controlling force. In this, as in most cases, the machinery, the source of 

 energy, and the controlling force are disconnected except when at work; butin the 

 body all three occur together in the same structure. 



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