300 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



riority in dimensions over the external elements (ulna 

 and fibula) in all the Diplarthra. The bones of the 

 inner side of the first carpal and tarsal rows have thus 

 transmitted an ever-increasing share of the impact, as 

 the radius and tibia have developed, and have grown 



Fig. 80. Fig. 81. 



Fig. 80. Rhinoceros unicornis carpus. Arrow ending in P, line of impact 

 in plantation; do. ending in A", line of strain in recover. 



Fig. 81. Equus caballus forefoot. Sc, scaphoid; L, lunar; Cu, cunei- 

 form; Tffz, trapezium and trapezoideo ; Un, unciform ; ing., magnum. 



with their growth at the expense of the external ele- 

 ments, the cuneiform in the carpus, and the calcaneum 

 in the tarsus, which have become very narrow elements 

 in the higher Diplarthra. As the pressure has been 

 obliquely from within outwards, the growth of the 

 proximal elements, the scaphoid and lunar in front, 



