Il] THE EXISTING EQUIDAE 81 



Equidae on African soil, it must not be assumed that the 

 disposition of stripes in the Grevy Zebra is original, and not 

 as in the case of the other species the result of modification 

 due to environment. 



Again, we have seen (p. 12) that the presence or absence 

 of hock callosities has been taken as one of the chief means of 

 differentiating Equus caballus from the asses and zebras, and 

 though zoologists are at variance regarding the primal use of 

 these excrescences, they are agreed in holding them to be 

 survivals from a remote ancestor. It is therefore to be carefully 

 noted, that whilst the hock callosities are present in Prejvalsky's 

 horse, and are especially of large size in domestic horses of 

 heavy breed, they are not unfrequently absent in North African 

 horses (and always absent in pure, and frequently in half-bred 

 ' Celtic ' ponies of the British Isles, the Faroes, and Iceland), 

 they are completely wanting in all the asses and zebras, or in 

 other words, in the wild Equidae of Africa (although the wild 

 ass of central Asia occasionally shows a vestige, p. 37). 



Finally, the true Prejvalsky horse and true tarpan have their 

 fetlocks and lower portion of the leg always black, whereas the 

 asses and zebras have their legs either white or covered with 

 dark and white stripes. It therefore follows that any one of 

 the Equidae which shows stripings all over its body and face, 

 white and black bands on the lower parts of the legs, and does 

 not possess hock callosities has a very strong prima facie claim 

 to be considered African in origin. 



R. H. 



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