PROBLEMS OF MODERN SCIENCE 



hinder part of the bone where it is opposed to the 

 ground. This set of bars is disposed exactly in 

 the direction of the lines of pressure to which the 

 heel-bone is subject when the body is in the 

 standing position. The second set of bars curves 

 upwards towards the back of the bone, and crosses 

 the pressure-bars at right angles. This second set 

 of bars obviously ties the pressure-bars together and 

 prevents their spreading or buckling. 



Fastened to the hinder part of the heel is a great 

 cord, easily recognisable and felt in one's own leg 

 as it extends downwards from the calf to the heel. 

 By means of this cord the calf-muscles are enabled 

 to pull upon the heel-bone and raise it from the 

 ground, as happens when standing upon the toes 

 and at every step in walking. The calf-muscles 

 are one of the most powerful muscular combinations 

 found in the body, and can exert an enormous 

 pull. This is readily understood when it is con- 

 sidered how easily the heel can be raised from the 

 ground even when one is standing on one leg. 

 Under these circumstances the calf-muscles of one 

 leg can lift nearly the whole weight of the body 

 with the greatest facility. As a consequence the 

 heel-bone is subject to an enormous strain when the 

 calf-muscles set to work and pull upon it. It is 

 enabled to withstand this strain owing to the disposi- 

 tion of the slender curving bars of the lattice-work, 

 which will be found to impinge upon the back 

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