26o THE HORSE AND ITS RELATIVES 



proboscis may have been developed in most or all 

 of the forerunners of the horse-group. 



Ag.iinst this view it may be urged ihAiHippidmm, 

 which probably had a proboscis like Onohippidmm 

 — as the skull-structure in the two genera is almost 

 identical — lacks a preorbital pit. As the various 

 opinions in regard to the function of that pit have 

 been fully discussed in the first chapter, no further 

 reference to the subject is necessary in this place. 



It remains, however, to add that a small species 

 of hipparion of slender build from the Pliocene 

 strata of the Siwalik Hills of Northern India, 

 described in the first half of the nineteenth century 

 by Messrs. Cautley and Falconer as Hippotheriuni 

 antilopimim [Hippot/ieriiifn being an alternative 

 name for Hipparion) is now believed to have lost 

 the lateral toes, and has accordingly been referred 

 to a genus by itself, under the name o{ Hippodactylus. 

 In addition to the typical Hippodactylus antilopinus, 

 there is a second Siwalik species, which has been 

 named H. chishohni,^ 



It may be added that in Hippariofi, as well 

 as in Alerychippus, the terminal bone of the main 

 toe has a cleft in the middle of its lower front 

 border ; this cleft occurring in many of the earlier 

 forerunners of the horse. 



All the foregoing genera may undoubtedly be 

 included in the same family — Equidce — as the 



^ G. Pilgrim, Rec. Geol. Surv. India, vol. xl. p. 67, 19 10. 



