CHAPTER XXII 
THE COMMON ZEBRA OR BONTE-QUAGGA 
Horse Family 
Equidce 
The living members of the Equidce 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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