CHAPTER X. 



THE TEETH OF UNGULATA. 



IN the two orders just considered, the Cetacea and 

 Edentata, a single set of teeth would seem to be the rule, 

 and most members of these orders are, so far as is known, 

 both monophyodont and homodont. But in all orders that 

 remain to be considered a Diphyodont dentition, the milk set 

 varying from the merest rudiments to full development, will 

 be the rule ; and being diphyodont, they are for the most 

 part heterodont, that is to say, the teeth differ from one 

 another, and we can distinguish them into incisors, canines, 

 premolars, and molars. Hence we are able to assign to them 

 a dental formula, and an extended survey of mammalian 

 forms lends strong support to the idea that the typical dental 

 formula, in which the full normal mammalian number of 

 teeth is present, is 



.31 43 



1 "3" c T prm T m 3~ 



Very many have less than this full number : only a few 

 have more ; and it is not a little interesting to find that 

 among extinct mammalia, and especially among extinct 

 ungulata, the typical dentition was more often present than 

 amongst recent animals. Indeed it may be said that most 

 mammals of the Eocene period had the full typical mam- 

 malian dentition. 



