566 



THE MAMMALIA OF THE UINTA FORMATION. 



■tfenodus. AnrliMieriuin /Ijlhelops^^ 



First. In Types II and III the unreduced, nearly isodaetyl and semiplanti- 

 grade form?, the Amhlypoda and Proboscidia, the unspecialized spreading toes trans- 

 mit the strain from eveiy side. We observe a marked increase in the 

 size of the lunar. Among the Proboscidia the lunar eithei' rests upon the 

 magnum only or upon the magnum and trapezoid ; this is the common condition ; or 

 upon the magnum, tiapezoid and unciform (see page 539). 



Second. In all the genera of the reduced types, excepting the highly spe- 

 cialized Types VI and VII, it is a remarkable fact that the scapho-magnum and 

 lunai- unciform facets ai'e subequal. It appears fi-om a comparison of the vast num- 

 ber of forms included in Types IV-VI, that reduction, altering as it does the entire 

 system of digital strains, has had some definite influence in limiting or widening the 

 extent of these facets, and that Prof. Cope has put the effect before the cause in 

 stating that displacement precedes reduction. Schlosser has rightly reversed this 

 relation.* 



The pei-manent tetradactyl condition in the perissodactyls of Type IV, like the 

 ai'tiodactyl didactylism is paraxonic, i. e., the greatest vertical strain is not trans- 

 mitted directly through the median toe but between the third and fourth toes, this, 

 with the lateial strain coming from the functional fifth toe, in some manner limits the 

 growth of the scaphoid and unciform, and in many instances results in the spreading 

 of the lunar in both directions ; it will be observed that in nearly every case the 

 lunar is directly in the mesaxonic line. AVhere tiie four toes sjjread, as in Titano- 

 tlierium, the metapodial strains must be somewhat analogous to those in the Probos- 

 cidia and Amblypoda — at all events the grow th of llie lunar in each instance suggests 

 such an analog3% 



As this condition of the lunar occurs in widely separated phyla and in a targe 



*0p. cit., p. lis : "Gleiclizeilis Jiiil tVwsi;r [{ciluUlicm iki- SfilciizcluMi liiuU-1 iuuli ciin- AcjuUTiiiig- in ilcr Anonl 

 liimg iler Cariiiiticii uiul Tiusalicn stall, '■ 



