CHAPTER XXII 



THE COMMON ZEBRA OR BONTE-QUAGGA 



Horse Family 



Equidce 



The living members of the Equidcs are distinguishable 

 from all other hoofed mammals by the single-toed charac- 

 ter of their feet. They represent the highest specialization 

 in foot structure of the odd-toed ungulates or perisso- 

 dactyles but are united by intermediate fossil forms to re- 

 mote five-toed ancestors of small size which lived during 

 the Lower Eocene in both Europe and North America. 

 Such ancient types showed little resemblance to the modern 

 horse, being diminutive, carnivore-like mammals the size of 

 a rabbit, and if they were not united by intermediate forms 

 their equine relationship would scarcely be suspected. The 

 family Equidce consists of horse-like genera having but a 

 single toe to each foot, the lateral toes being represented by 

 the splint-bones, which have lost all trace of false hoofs at 

 their tips. The forms having three toes comprise a dis- 

 tinct family of fossil horses intermediate between true 

 horses and the diminutive five-toed ones. The dental ap- 

 paratus of the modern horses also shows much specializa- 

 tion. It is especially fitted to withstand a great amount 

 of wear due to mastication. To serve this purpose all the 

 cheek-teeth have become very long-crowned ; the crowns at 

 their tips being broad and composed of alternate layers of 



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