36 



THE INDIVIDUAL ORGANISM 



of the hand and arm of man, and especially the ability to grasp and 

 manipulate objects, have evidently had much to do with the develop- 

 ment of his mentality and attainment of the dominant position that he 

 now holds in the world. 



Fig. 3.6. The bones of the arm, showing the joints and movements involved in turning the 

 wrist. 



The pelvic girdle and the leg. The pelvic girdle has the form of a 

 large and irregularly symmetrical bony ring. It is made up of three pairs 

 of strongly fused bones — the ilium, or hipbone, the ischium (on which we 

 sit), and the pubis (in front). On each side of the pelvic girdle there is a 

 deep socket called the acetabulum, into which fits the rotatable ball-like 

 head of the femur or thighbone. The shape of the pelvis differs slightly 

 in the two sexes. That of the male is somewhat narrower, deeper, and 



