TlIK MAMMALIA OP THE UIN'TA FORMATION. 535 



Prol)oscidia.* The distal row of carpals was probably much broader than the prox- 

 imal, and the metapodials, as in the pes, were without any lateral facets. 



General Modification of the Fee^. 



The {irimitive structure, as Cope has shown, is ai)proximatcly preserved in the 

 plantigrade Jli/rax, showin<^ that all the secondary articulations in various un<^ulates 

 were adaptations to digitigradisni. There are four stages in the foot elevation : 

 First, the plantigrade, already described; then the s e m i p 1 a n t i g r ade, 

 seen in the feet of the Proboscidia and Dinocerata, with short slanting metapodials 

 well raised proximally. Kutiraej'er has proposed ''digitiplantigrade " for the reduced 

 types with elongate vertical metapodials in which the phalanges rest fully upon the 

 ground {Ccmtelus). As this condition is practically analogous to that in one division 

 of the Carnivora, it may be more simply described as d i g i t i g r a d e. There arc of 

 course many steps between this condition and the u n g u 1 i gr a d e foot, in which 

 the terminal phalanges alone rest upon the ground (^Eipim^). 



The universal result of elevation of the wrist and ankle joints was displace- 

 m c n t in some form, from the serial ordei', adapting the foot bones to the new inci- 

 dence of impacts and strains. Then came reduction of one of the lower leg bones 

 and of the lateral digits. With one exception, seen in the proboscidian manus, the 

 departure from the serial tyi)e was upon a single principle : First,t the ii and in 

 metacarpals and metatarsals a c q u i r e d late r a 1 s u j) [) o i- 1 i n g 

 facets upon the second row of p o d i a 1 elements, usually u})on 

 the outer side. Second, the bones of the upi)er row of carpals and 

 tarsals formed articulations with the more octal eleniuiits of 

 the second row. 



Til the general modilications of the Maxl'S it is important to note that nu-s. ir 

 and III invariably accjuired supporting facets upon the octal side with tiie magnum 

 and unciform respectively. Excej^ting in the scmiplantigrade orders the reduction 

 of the first digit was very lapid, it being already absent or functionlcss in the 

 Eocene Diplarthra. The extension of the lunar was the next step in displacement ; 

 spreading upon the trapezoid in the Proboscidia, or upon (lie unciform, by its own 

 giowth or that of the unciform beneath it, in all other ungulates. This is inci])ient in 

 P/^eHacorfM.-* and extensive in the Arablypoda. In other phyla tlu- displacement ol 



• Riilinieyer, Uuber einige Buzieliiingcn zwischen ilcn SiiiigcUiicrslnmmcn Alter iind Neuer Welt, Zurich, KVSM. 



tSccMnrali, nimxiTaHi, |>. is:i, ^ 3 . Tlint Uic mctn|>ni1liil dhpliirfinrnt wiis iimrr |iriinilivc timn llw |><>ilml In 

 shown both in P/ien'foilu» iind /lyr<ir, in which mk-9. ii und III aliut laliriilly iigiiin^^l il.' m .-iniiii iiikI iinrilorni, while 

 the carpals arc serial. 



