54G THE MAMMALIA OF THE UINTA FORMATION. 



Through the Eocene series, the latei-al toes are not more rolled backwards than in 

 H. venticolum. 



In MesoMpjms, the most marked development is seen : first, in the flattening of the 

 cuneifoi-ms ; the entocuneiform is united with the mesocuneiform, but does not sup- 

 port mt. u ; second, the tarso-metatai-sal articulation is absolutely of the plane serial 

 type; third, the lateral digits and corresponding tarsal elements are rolled backwards 

 so that the outer elements are almost or quite in contact posteriorly, the cuboid 

 touching the entocuneiform. The fibulo-calcaneal facet is always distinct. In the 

 astragalus the ectal and sustentacular facets become nearly confluent; the astra- 

 galo-cuboidal facet is reduced to a small narrow triangle placed in front. The seven 

 astragali examined (Princeton (JolL, ISTo. 10,255), apparently represent two species, 

 in one of which, the smaller, the fossa upon the astragalo-naviculai' is faint ; the 

 larger species shows this fossa very distinctly (Prince. Coll., No. 10,250). This 

 may, however, be not a specific but an age chai-actei'. 



The serial metatarsal articulation is an extremely interesting feature, when we 

 compare this tarsus with that of Ily racotherium and PliolopJms ; it precedes the growth 

 of mt. in ui)on the cuboid in AncMtherimn, an altogether difl:erent process from the 

 lateral displacement seen in the above Eocene forms. 



It is not necessary here to go over in detail the ground made familiar b}' the 

 memoirs of Kowalevsky and Forsyth Major,* of the subsequent evolution of the 

 pes; in fact, the material from American strata for such a purpose is not at present 

 accessible. 



3. The IIyrachyus, Triplopus, Hyracodont Series. 



There is an intermingling of i-hinocerotic and equine characteristics in the teeth 

 and feet respectively of this series, which give it an especial interest and separate it 

 widely fi-om both the above stocks. It has nothing in common with the tapir series 

 either in the structure cf the teeth or feet, and unlike both the tapirine and equine 

 lines, little is known of the sub-Biidger forms, and there is no parallel European 

 phylum. 



The general characteristics of the carpus and tarsus are the vertical elongation 

 and lateral compi-ession of the elements of each and the close union of the metapo- 

 dials in some of the later forms, which, while tridactyl, renders the foot in some 

 forms functionally monodactyl. 



* AL-conlini; to Kowulcvsky (Anchilh., PI. II, Fig. 20A . . ), Uio octo- and mcsomiipilbrms unite in AnchUherimn, 

 liut ;ire distinct in Hipparion (Antlinu-iillici-., ]). 104). According to Forsyth Majm- (IJoit. z. Gcsch. d. toss. Pferde. II 

 Til., p. 62), the union of c-n. 1 imd 3 is tin' lulu and of cii. 2 and 'A tliu fafc exception. 



