STANDING AND WALKING 427 



the pelvis on the hip-joint. Just try to l)aUincc an articulated 

 skeleton on its two feet and you will get some idea of the com- 

 plexity of the process. P^^ach foot has three points of contact 

 with the ground, viz. heel, base of hallux, and varying proportions 

 of the outer digits. Thus, the body is balanced on two tripods 

 (Fig, 52). These tripods can be placed in various positions 

 relative to one another so as to spread the area of support and keep 

 the plumb from the centre of gravity within it. With the feet in 

 the position adopted when one stands erect and at ease, one has got 

 to place the tibia? on the tripods so that the centre of gravity of 

 the parts superior to the ankle-joint lies as nearly as possible over 

 the axis of the joint. Having done this, we have, in a similar way 

 to balance the femur, and then the pelvis with vertebral column, 

 thoracic cage and arms. Finally, the head has to be placed on 

 the atlas. 



Bending. The further the vertical from the centre of gravity 

 moves from this " at ease " position, the greater is the difficulty of 

 maintaining equilibrium. More muscles are called into play and 

 they have to bear a greater load. Fatigue, which we have seen is 

 rapidly produced by continuous exertion, soon sets in. 



In bending forward the centre of gravity passes forward out of 

 the body and lies well in front of it. To counterbalance this, the 

 hips are thrust back and the body assumes a > position. If this 

 is not done, we would fall forward, as any one may find out if he 

 tries to pick from the floor a coin placed between his feet, protrusion 

 to the posterior being prevented by standing against a wall. This 

 function of the hip movement is apparent also when one tries to 

 stand on one foot. On shifting from both feet to one foot, the hips 

 shift towards that side on which the foot is being used, and com- 

 pensatory movements of the shoulders and other parts occur. If 

 one stands vertically upright, heels against a wall which prevents 

 the backward movement of the hip, it is just as impossible to stand 

 on one foot as it is to touch the toes without falling. 



Walking, The process of walking is a series of acts whereby a 

 state of unstable equilibrium is first produced, and then corrected 

 by altering the position of the underpropping area of the body. 

 It might be described as falling forward followed by recovery. It 

 has been extensively studied by Hill and others by means of the 

 ultra-rapid cinematograph camera producing the so-called " slow- 

 motion " pictures. These records show that, from the standing 

 position, natural walking is accomplished by leaning forward and 

 when the angle of slant assumes a critical value indirectly related 

 to the height of the walker's centre of gravity from the ground, one 

 foot is raised, swung forward, and its heel placed on the ground. 



