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U.S. NATIONAL MUSEUM BULLETIN 2 73 



Figure 42. — a, By the action of the erector spinae the vertebral column and the pelvis are 

 transformed into a rigid column that tends to tilt forward due to its own weight and those 

 of the skull and enlarged neck structure. The insertion of the erector spinae on the iliac 

 crest extends this effect down to the iliofemoral joint on whose transverse axis the tilting 

 would take place, b, The gluteus medius pulls the ilium and therefore the trunk back. 



