64 



ARBOREAL MAN 



manent twist, such as is seen to perfection in the capsule 

 of the human hip-joint (see Fig. 22), and the muscles 

 (e.g., the M. rectus femoris) dispose themselves to the 

 best mechanical advantage for performing the move- 

 ments of the joint. 



FIG. 22. THE HUMAN HIP-JOINT FROM BEHIND, TO SHOW 

 TWISTING OF THE FIBRES OF THE CAPSULE OF THE JOINT. 



When the leg has become rotated backwards, and the 

 muscles and joints have adapted themselves to this 

 change, there still has to be an elaboration of the support- 

 ing mechanism in this new position. These forces are 

 all in action during arboreal life, but they gain an added 

 importance in the habitual orthograde posture of Man. 



