260 



ANIMAL MECHANICS. 



of gravity alternately behind' and in front of it, we shall gradually 

 reach the plumb-line and carry the runner balanced on the lever. It is 

 quite easy to determine this to within 3 cm. By arranging a plumb- 

 line to fall through this point, as in Fig. 146, we can determine by 

 photography the relation between the centre of gravity and the centres 

 of rotation of the joints previously determined. 



Braune and Fischer, as we have seen, give as the Normal-stcllung 

 that erect posture in which all the axes of rotation of the joints 

 lie in the same frontal plane. In this position the centre of gravity 

 of the body is found by them to fall in the same plane. This we 



failed to verify, though the deviation from the plane 

 is not a great one. In the case of a well-built 

 soldier (Fig. 148), the centre of gravity was 1*5 cms. 

 in front of it. While in the individual of normal 

 build there is not that strict relationship between 

 the position of the centre of gravity and the joints 

 which Braune and Fischer maintain, it is certain 

 that in many abnormal figures, and with women 

 in pregnancy, the centre of gravity must lie well 

 away from the plane containing these joints when 

 they are placed in what is called the Normal- 



stellwig. 

 The 

 assumed 

 without 



Fig. 146. — The posture is 

 arranged that the dots 

 indicating the centres 

 of rotation of the 

 principal joints fall in 

 the same vertical plane, 

 which is indicated by 



erect position. — The brothers Weber 

 that the erect position was maintained 

 or nearly without muscular exertion. 

 They found reasons for believing that every part 

 of the body might be sustained by the tension of 

 ligaments. As long as the centre of rotation of 

 the knee is in front of the line between hip and 

 ankle-joint, the body weight pressing on the hip- 

 joint will cause the leg to be bent at the knee. But 

 if extension of the knee be carried so far that the 

 centre of rotation falls behind the line mentioned, 

 the body weight will only tend to produce over- 

 extension, and the knee will be kept rigid by its 



dividual slightly 

 front of that plane. 



the vertical line. The powerful check ligaments. In the same way the 

 SStVaSX body may easily bend forward on the hip-joints if 

 centre of gravity of the its centre of gravity plumbs before these joints, 

 body falls in this in- but if it plumbs behind, the pelvis and spine can 

 111 only rotate backwards until the check ligaments of 

 the hip come into play. The head was believed by 

 Weber to be exactly balanced on the atlas in its normal position. Thus 

 the whole body would be sustained in the erect position without inter- 

 vention of muscles, provided it were poised in equilibrium on the 

 ankle-joints. 



Now, according to the brothers Weber, the centre of gravity plumbs 

 behind the hip, in front of the knee, and above the ankle-joint, when 

 the body is standing in the position of greatest ease. For this reason 

 muscular effort is only required to establish and retain the position 

 described. Meyer agrees in the main with the Webers, except that he 

 states that the centre plumbs in front of the ankle-joint, thus calling 

 upon the extended calf muscles to contribute towards the support of the 

 body. Meyer, moreover, places the centre of gravity of the head 



