xx THE HORSE IN HISTORY 



modern thoroughbred, for letters of introduction, 

 etc. ; and the Directors of the British Museum 

 and the Directors of the National Gallery for 

 allowing photographs to be taken for reproduc- 

 tion. For the sake of convenience the centuries 

 B.C. are alluded to in the same way that centuries 

 a.d. are alluded to, that is, one century in ad- 

 vance. Thus 550 B.C. is spoken of as the fourth 

 century B.C. ; 250 a.d. as the third century a.d., 

 and so on. 



