42 THE INFANCY OF ANIMALS 



dentition of more remote ancestors. This is shown in 

 the case of the fossil horse Merychippus, where the milk 

 teeth are of the short-crowned type, lacking the " cement " 

 seen in the yet older fossil species Anchitherium, whereas 

 the teeth of the later, permanent set of Merychippus show 

 the high-crowned cemented type characteristic of the 

 more specialised members of the family Equidae. 



Again, the grinders or cheek-teeth of the milk series 

 of the Wart-hog (Phacochesrus) are numerous, as in 

 typical pigs, but in the adult wart-hog aU are finally lost 

 save the hindmost molar, which is of huge size, recalling 

 in many respects that' of the elephant. 



In those extraordinarily coloured creatures the " Ratels " 

 — iron-grey above and black below — the chief grinder or 

 " carnassial " of the milk-set differs conspicuously from that 

 of the adult, and resembles that of the permanent carnassial 

 of the more lowly Galictis. Among the majority of the 

 marsupials only one milk-tooth in each jaw is present, 

 answering to the last of the grinders of the milk series, 

 and this is more complex in character than the tooth 

 which finally replaces it. For a long while it remained 

 a moot point whether this tooth was to be regarded as 

 the precursor of a milk-dentition, or was the last sur- 

 vivor of a set of " milk-teeth " to be finally eliminated. 

 Most authorities inclined to the view that the marsupials 

 retained their milk-teeth throughout life, with the ex- 

 ception of the one replacing tooth, which was regarded 

 as the first member of a dentition answering to the per- 

 manent dentition of other groups, including Man himself. 



We now know that this view was incorrect ; that the 

 tooth in question is the only one of a complete series 

 to come to perfection ; for in some of the marsupials 

 rudiments, or more correctly vestiges, of a complete set 



