422 CLASSIFICATION OF THE EQUID.-E. 



Prjevalsky's horse. One of these, a kiang - Exmoor- mare 

 hybrid, among other differences, brayed hke his asinine 

 sire, and had no chestnuts (p. 319) on his hind legs. 

 Prjevalsky's horse, on the contrary, neighs hke the 

 domestic horse, and has relatively longer chestnuts on his 

 posterior limbs. Also, his mode of living (p. 641) conclu- 

 sively shows that he is not a hybrid. As the zoological 

 name of the domestic horse is Equus caballus, the best 

 designation for Prjevalsky's horse, with our present defec- 

 tive knowledge, is probably Equus caballus, prjevalskii. 

 It appears that the Tarpan (p. 648) is or was a variety 

 of Equus caballus. 



In passing from varieties to breeds, we again encounter 

 the difficulty of drawing distinctions, which, in this case, 

 are not clearly enough defined to be absolute. As far as 

 I can learn, no attempt has been made to separate ponies 

 from horses, except on the purely artificial basis of height, 

 which is of an extremely variable nature, as we have 

 seen in the preceding chapter. Sanson regards the North 

 African horse as a special variety, and calls this animal 

 Equus caballus africanus. In support of this view, he 

 avers that this horse has only five lumbar vertebrae, 

 instead of the usual six ; and that it has no chestnuts 

 on its hind legs. This attempted distinction with regard 

 to the number of the loin vertebrae is not valid, because 

 we not unfrequently find only five loin vertebrae in other 

 breeds, as for instance, in the case of the famous thorough- 

 bred, Orlando, whose skeleton is in the Museum of the 

 R.C.S., Lincoln's Inn Fields. Salensky tells us that Prje- 

 valsky's horse has only five loin vertebrae. Stnithers 

 {Jour. Altai . Phys ), Bateson (Materials for the Study of 

 Variation) and other biologists have shown that in all 

 vertebrate animals, man included, the number of loin 

 vertebrae is subject to variation. The absence of chest- 

 nuts in the hind legs is not confined to the North African 

 horse. Professor Ewart has shown that both ergots and 

 hind chestnuts are often absent in the ponies of Iceland, 



