70 



HUMAN BIOLOGY 



extending and pushing, the left fore limb is flexing and 

 pulling; meanwhile the weight is swinging between the 

 left hind limb and the right fore limb, the pelvis is turned 



^"^^ 



r^l 



a^ 



N, 





yz,u^ 



WTO 



■#k: 



Fig. io. Primitive reptilian and primitive mammalian postures. 



A. Primitive reptile {Seymour'xa) of Permocarboniferous age. 



B. Primitive mammal (opossum), survivor of Cretaceous marsupial stock. 



(From Gregory, Proc. Amtr. Pbilos. Soc.) 



slightly toward the right, while the pectoral girdle is turning 

 in the opposite direction; both are also being rocked trans- 

 versely in opposite directions. 



