MOTIONS OF THE SKELETON. 39' 



CHAPTER IX. 



OBSERVATIONS ON THE MOTIONS OF THE SKELETON. 



The falling down of the body during life, when muscular 

 action is suspended, as well as the examination of the artificial 

 skeleton, evince that this machine is not constructed to preserve 

 the erect position of itself; but that, when unsupported, it bends 

 at the joints, and invariably falls forward. 



It is retained in the erect position by the action of muscles : 

 and that the muscles should produce this effect, it is necessary 

 that they should have a fixed basis to act from. 



This basis is the feet, and they are fixed to the ground by 

 the weight of the body. 



To keep the body from falling, it is necessary that the centre 

 of gravity should be immediately over the centre of the common 

 basis. 



All our movements, both in walking, standing, and rising 

 from our seats, are regulated by this principle ; and whenever 

 we move our body, so that the centre of gravity is changed, 

 we must change the position of the feet, that the centre of the 

 basis may be directly under it. 



If this proposition were not almost self-evident, it might be 

 illustrated by several very easy experiments. 



If a person stand against a wall with his heels and the back 

 parts of his legs and thighs in contact with it, and, in this situa- 

 tion, attempts to stoop forward, he will fall upon his face ; there 

 Is no power in his muscles, or in any other part of the body, 

 when thus circumstanced, to prevent it ; but a small movement 

 forward of one foot, will enable him to stoop with ease by 

 tiltering the basis of the body. 



When we sit in such a position that we cannot bring the 

 Centre of gravity over the feet, the lower limbs are divested of 

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