10 THE ANCESTORS [CH. 



the Equidae on the American continent was due solely to the 

 insect scourge of modern Paraguay. But as it is clear that 

 though lions abounded in South Africa and preyed largely on 

 zebras, they never threatened extermination to the horse family 

 in Africa, whilst on the other hand the tsetse-fly and horse 

 sickness are as deadly to Equus caballus in certain areas of that 

 region as is the insect pest of Paraguay, it seems far more 

 probable that the extinction of the horses of North and South 

 America was due to the inroads of mean and obscure forms 

 of life rather than to the onslaughts of the great flesh-eating 

 monsters of the young world's prime. 



It is generally admitted that the ancestors of the living 

 Equidae passed from America into the Old World, for before 

 the Ice Age it was perfectly possible for American horses to 

 cross into Asia by land bridges in the vicinity of Behring's 

 Straits ; thence they extended into Europe, and finally reached 

 Africa either from Asia or by the land bridges which then 

 linked Europe to North Africa. "One of the earlier immi- 

 grants, Equus stenonis, has left its remains in Pliocene deposits 

 of Britain, France, Switzerland, Italy, and the north of Africa. 

 While E. stenonis was extending its range into Europe and 

 Africa, two others, E. sivalensis and E. namadicus, were finding 

 their way into India, and yet other species were doubtless 

 settling in Eastern Europe and Central Asia 1 ." Thus, as Africa 

 now contains several species of zebras, so Europe at the 

 Pleistocene period was inhabited by several species of horses. 

 Some palaeontologists believe that the Indian species E. siva- 

 lensis and E. namadicus became extinct, and that E. stenonis 

 gave rise through one variety (E. robustus) to the modern 

 domestic breeds, and by another (E. ligeris) to the Burchell 

 group of zebras. Hipparion and certain prehistoric South 

 American species were characterised by a fossa or depression 

 in front of the orbit for a facial gland (probably similar to the 

 scent gland in the stag), found also in E. stenonis* and its later 

 ally E. quaggoides and in E. sivalensis (cf. p. 1 50). 



In some modern horses, which have so-called Eastern blood 



1 J. C. Ewart, op. cit. p. 3. 



2 E. W. Lydekker, Proc. Zool. Soc. (1904), Vol. i. p. 427. 



