ODD-TOED UNGULATKS (pERISSODACTYLa) 271 



nppiiratus for mastication, wliile the brain case is 

 relatively small. The teeth are highly specialised 

 and complex with very long crowns. 'J'here are 

 infoldings of enamel filled in with dentine and cement 

 on the snrfaces, not only of the molars, but the 

 incisors, forming what is technically known, in the 

 latter, as the " mark.'^ The '' mark " is a pit on the 

 surface of the incisors which gradually becomes 

 obliterated as the tootli wears away, therefore its 

 presence is a guide to the age of the aiiitnal. In 

 the adult horse there are six incisors in each jaw. 

 Two canines or ^' tushes " are present in eacli jaw of 

 the male only. There is a toothless gap or diastema 

 in the jaws between the canines and the cheek 

 teeth, commonl}^ known as the " bar '' in the lower 

 jaw. Man has taken advantage of this natural space 

 between the teeth for the insertion of the bit. The 

 first of the four premolars is very much reduced and 

 often absent. They are known popularly as wolf- 

 teeth, and their presence is supposed to bring not 

 only ill-luck to their possessor, but to affect his sight 

 and otherwise injure his health, and they are usually 

 removed by the farriers. The other three premolars 

 and the three true molars grow close together and 

 form a solid grinding surface, like natural mill-stones. 

 They always maintain the same level, the teeth 

 pushing outwards from their sockets to compensate for 

 the wearing down of their grinding surfaces. The 

 permanent teeth are preceded by a set of milk teeth, 

 consisting of six incisors and six molars in each jaw. 

 The milk teeth begin to come through soon after birth, 

 and the young horse has his complete set of twenty- 



