210 THE MAMMALIA. 



It is only in its historical connection that the 

 peculiarity of the horse's dentition acquires a 

 peculiarly significant interest, and as in the case 

 of the three-toed foot when viewed apart from the 

 historical course of its development, seems simply 

 an incomprehensible peculiarity, of no importance 

 either to the horse itself or to the horse fancier . 

 Palseotherium, Anchitherium, and Hipparion pos- 

 sess, when full grown, seven cheek-teeth above and 



below on both sides of the jaw, p -, m r . On the 

 other hand the normal formula in the horse's den- 



q q 



tition is p -, m -; it changes only three of its 

 o o 



milk-teeth, and gets three other molars. Now it 

 has long since been known to breeders and veterinary 

 surgeons that, pretty frequently, the horse's row 

 of cheek-teeth begins with one stump too many, 

 the so-called 'wolf's tooth' (on Owen's drawing 

 marked by the letter p). This most perfectly ex- 

 presses the fact that it occupies the place where, 

 in Palseotherium among others, we have the first 

 premolar. When it appears in the horse, however, 

 the wolf s-tooth ' is not deciduous. It is most 

 obviously a tooth in the last stage of disappear- 

 ance, an irregularly appearing descendant from the 





