ANIMAL DENTISTRY. 49 



set on its way toward maturit3^ (Thus far dental evolution 

 does not vary materially in the different species). 



EVOLUTION OF THE TEMPORARY TEETH. 



This period of dental evolution begins when the milk 

 teeth make their first appearance on the buccal surface, and 

 ends- when they are entirely replaced by their permanent 

 successors. In some animals the temporary teeth erupt be- 

 fore birth. It is, however, at the time of birth or within a 

 few days after that the first evidence of temporary dentition 

 appears in all domestic animals. The end of the period 

 varies with each species. In the horse the last temporary 

 teeth disappear at four and a half years of age. Thus the 

 period in the horse lasts from birth to four and a half years 

 of age, in the ox from birth to four and a half years, in the 

 sheep from birth to three and a half years, in the dog from 

 birth to six months, and in the pig from birth to three years. 

 In all the domestic animals except the dog the temporary 

 incisors persist longer than the molars. 



THE HORSE. 



The central incisors erupt before birth or, in some in- 

 stances, within a few days after. They are large, white 

 teeth, occupying the entire incisor arcade and contact their 

 opposing teeth by their anterior borders only. The pos- 

 terior border is still hidden beneath the gums and only 

 comes to the level of the anterior border after three months' 

 wear, at which time they present the typical table of an 

 herbivorous incisor. The cup is deep and distinct, and in its 

 whole appearance cannot be readily recognized from that of 

 a permanent incisor. At the earliest period after eruption 

 two influences are at work for their destruction — the perma- 

 nent tooth is gradually encroaching upon its fang while the 

 crown is becoming shorter and shorter under the influence 



