564. 



THE MAMMAIJA OF THE UINTA FORMATION. 



received the maximum pressure nud lateral straiu. At the same time, the eetal or 

 ulnar side of the upper row and ental or i-adial side of the second row received a 

 diminished pressure and strain by the reduction of the ulna and loss of the first digit 

 respectively.* At all events the scaphoid grew outwards and the unciform grew 

 inwards in all the Diplarthra ; they thrust the lunar and magnum apart over the 

 unciform and beneath the scaphoid respectively, in many cases without any actual or 

 relative increase in the size of these elements, as demonstrated by the extremely, 

 small size of both the magnum and lunar in the greatly displaced carpus of Triplo- 

 pus or Ilyracodoii. Thus what appears to be a rutation of the bones of the uppei- 



rhermcodiis 



//asiodon 



Den c/roh vf^hx 



DiAO. 8.— The displarpiiient of \\w. bones of Ihe manus in the Unsuleita, I. Phemicodus primii'i;m, from original 

 in the Cope collection. Coryphodon hamalus, after ]\Iarsh. Dendrohyrax arborcns, from orii;inal in the Princeton col- 

 lection. Macrauchenia palmhonica, adar Gcxxsns. Mastodon Americaniis from original in Princeton collection. The 

 oblique arrows indicate the direction of displacement. 



row upon the second row, is in reality the growth of the scaphoid and unciform to- 

 wards the median axis of the foot. This is cai-riod to its extreme in tlic tridactyl 

 Perissodactyla, in which the mesial borders of the uncifoi-m and scaphoid are almost 

 ill contact in the mesaxial line, i. e., in the line carried througli the middle toe. 



This explanation is still inadequate, because we find, first, that under cer- 

 tain conditions the lunar shows a marked tendency to expand, and secondly, 

 the mesial growth of the scaphoid and unciform ceases. 



* A convenient illiHU-a',ii)n of the elVccl of digital rodncliDU upon the c,iri).ds was rem irkcd liy Dr. Scolt in Hie 

 reduction of the scaphoid in llic inadaptively reduced Artiodactyla— the scaphoid resting upon the trapezoid and nio 

 trapezium supporting tlie fnnctionlcss second digit only. 



