34 THE HORSE AND ITS RELATIVES 



the front end of the anterior premolar ; and, more 

 rarely, there may be a still smaller tooth in a 

 corresponding position in the lower jaw. These 

 small functionless teeth, which have no temporary 

 predecessors, and are known to horse-dealers as 

 " wolf-teeth," may be developed on only one side of 

 the jaw. They are the vanishing representatives of 

 teeth which were relatively large and functional in 

 some of the extinct ancestors of the horse, and are 

 of importance as showing that the three large 

 functional premolars of the latter correspond to the 

 three last of the typical mammalian series of four. 

 Hence it is frequently found convenient to speak 

 of these teeth as the second, third, and fourth pre- 

 molars, instead of calling them the first, second, and 

 third. On the other hand the three pairs of molars 

 are respectively denominated the first, second, and 

 third. 



In a young colt, if the " wolf-teeth" be not de- 

 veloped, there are three pairs of milk-molars in each 

 jaw ; those of the upper jaw having their crowns 

 more elongated from front to back than is the case 

 with the premolars by which they are subsequently 

 replaced. As the colt grows older, the first molar 

 cuts the gum before the last premolar has replaced 

 the corresponding milk-molar ; and, as a conse- 

 quence of this, it will always be found in an adult 

 horse that the crown of the first molar is rather 

 more worn than that of the tooth immediately in 



