THE SKELETON 



67 



is obtained at the expense of flexibility. The pelvic arch (Figs. 30 

 and 34) is not only heavy and strong, but is very firmly fixed to 

 the axial skeleton, the sacrum and os innominatum becoming in 

 mature life practically one bone. The socket into which the head 





FIG. 31. FIG. 32. 



FIG. 31. The bones of the arm. a, humerus; 6, ulna; c, radius; d, the carpus; 

 e, the fifth metacarpil; /, the three phalanges of the fifth digit (little finger). 



FIG. 32. Bones oi the leg. a, femur; 6, tibia; c, fibula; d, tarsal bones; e, meta- 

 tarsal bones; /, phalanges; g, patella. 



of the femur fits is much deeper than that which receives the 

 head of the humerus, rendering the leg much less liable to dislo- 

 cation than the arm, but at the same time restricting its move- 

 ments much more. The foot also in becoming adapted to form a 



