118 STRUCTURE OF TEETH 



above the gum ; a portion of it also passes over their 

 upper surface, and bending inwards, is sunk into the 

 body of the tooth itself, forming a kind of pit in 

 them. It is the inside and bottom of this which 

 constitutes what is called the ' mark,' and this mark, 

 by wearing down, enables the age of a horse to be 

 ascertained. Dealers talk of the filling up of the 

 teeth. This is nonsense ; the mark never fills up, but 

 the ridge of enamel round it is worn down; and the 

 discolouration, caused by the action of the food, is also 

 rubbed off. 



The colt's nipping teeth are rounded in front, re- 

 curved, being somewhat hollow towards the mouth, 

 and present at first a cutting surface, with the outer 

 edge rising in a slanting direction above the inner 

 edge. This, however, soon begins to wear down, until 

 both surfaces are level, and the ' mark,' which was 

 originally long and narrow, becomes shorter, and 

 wider, and fainter. 



At six months the four central nippers in both 

 upper and lower jaws are beginning to wear level, and 

 the corner teeth are quite so. The mark in the two 

 middle teeth is wide and indistinct, in the two next to 

 them it is darker, and longer, and narrower, and in the 

 corner teeth its colour, width, and length are most 

 marked. 



At the age of eighteen months the mark in the 

 central nippers will be fainter and shorter, that in the 

 two other pairs will have undergone evident change, 

 and all will be fiat, and at two years old this change 

 will be still more manifest. About this time an 

 additional ' grinder ' makes its appearance and another 

 process takes place. Up to the present time the first 



