336 



THE HUMAN MOTOR 



The two German savants, above mentioned, investigated f 1 ) 

 by photographic means, this question of 

 the centre of gravity of the various members 

 of the human body. The subject of their 

 experiments weighed 58-4 kg. The results 

 of their analysis were as follows : 



In the " easy attitude " (Bequeme 

 Haltung) the centre of gravity of the head 

 lies 5 mm. in front of the atlanto-occipital 

 joint. The head is therefore somewhat 

 out of balance longitudinally, and, to a 

 slight degree, laterally. This explains the 

 functions of the muscles of the neck in 

 maintaining equilibrium, and also the well- 

 known fact that the head falls forward on 

 the chest during sleep. The trunk may 

 be considered as a mass capable of move- 

 ment around a transverse axis passing 

 through the hip joints. It carries the two 

 arms which hang vertically. 



The common centre of gravity of the 

 trunk, arms, and head combined (vide 

 20) was found to lie at 18 cm. above the 

 axis of the hips, and 8-6 mm. in advance 

 of the frontal plane. For the whole bust 

 the moment of rotation M = P X -0086. 



The weight P totals 36-82 kg. of which 

 the separate items are as follows : 



Fio. 236.' 



Head 



Trunk 



Arm 



WEIGHT IN 

 KG. 



4-140 



25-060 



3-810 



3-810 



PERCENTAGE OF 



TOTAL WEIGHT 



OF BODY. 



7-1 

 42-92 



6-52 



6-52 



63-06% 



(of which 3-14% is 

 the forearm.) 



Bust (total)... 36-820 



The bust is retained in an erect position by the muscles of the 

 back and the abdomen. Its weight (63% of that of the whole 

 body) is transmitted to the hips. As its centre of gravity lies in 

 front of the axis of the hips the weight tends to thrust back the 

 thighs at their lower extremities (B in fig. 236). These latter 

 transmit the pressure to the knee-joints. These joints stiffen them- 



(*) Braune and Fischer (Abhandl . . . vol. xv., No. 7, pp. 631 and 635). 



