POSITION AND STRUCTURE OF HORSE 31 



pair. About half a year later the permanent tusks, 

 or canines, make their appearance in the case of 

 stallions. By the end of the fifth year the third or 

 outermost pair of permanent incisors will have re- 

 placed the corresponding temporary pair ; and the 

 dentition of the front of the mouth will consequently 

 be complete. It will be obvious that of the three 

 pairs of upper permanent incisors, the crowns of 

 the first pair will, after all are in place, be more 

 worn than those of the second, and the second more 

 than those of the third. As a rule, the mark dis- 

 appears in the first pair of lower permanent incisors 

 when the horse is six years old ; in the second pair 

 it is worn out a year later ; and in the third pair at 

 eight years. In the corresponding upper teeth it 

 persists about two years longer in each instance. 

 In the case of a six-years' -old horse the third lower 

 incisors retain large and conspicuous marks. Up 

 to five years the age of a horse can be determined 

 with comparative accuracy, and it can also be 

 approximately ascertained for some years later. 



When the mark has been worn out in all the 

 incisors, age-determination is no longer possible by 

 means of the teeth. It appears, however, that in 

 very old horses a kind of spurious mark is formed 

 by the tooth becoming so worn down that the 

 summit of the pulp-cavity at its base is exposed in 

 the centre of the crown. Such a mark lacks, how- 

 ever, the ring of enamel characteristic of the true 



