THE AGE. 435 



until after eight years of age. The following is the appearance 

 of the mouth at one year old. 



The four middle teeth have become level with each other 

 previous to this time, and the third pair, or 

 corner ones, are approaching the level of 

 the others. They present, respectively, the 

 following appearance: in the front pair, or, 

 two middle teeth, the mark is worn, being 

 somewhat dim, but broad and regular, with a 

 ring of enamel of very regular width, but 

 thicker in front than behind, surrounding it. 

 The mark is partly worn out of the next two, 

 or second pair, but it is darker, longer, and narrower than in 

 the first, and the ring of enamel surrounding it is not so regu- 

 lar. In the corner teeth the mark is of full depth, darker, 

 longer, and narrower than in either of the others, the rino- of 

 enamel being heavier and more . irregular. At this time 

 another pair of grinders in each jaw make their appearance, 

 making four in each jaw, on each side, or sixteen in all. 



At this age, and for some time after, as indeed previous to 

 this, the outer, or front, edge of the nippers is short, and the 

 flat crown shelving or slanting backward to the inner side, so 

 that the outer edges come together, while the inner edges do 

 not meet. This is evidently intended to facilitate the cutting 

 process for the young animal, who is generally required to ob- 

 tain his food from pasture, and not from the rack or manger. 

 And we here have another exemplification of that admirable 

 adaptation of means to ends, so frequently met with in the in- 

 vestigation of nature. 



Soon the sharp edge commences to wear down, but the colt 

 is growing stronger, ■ and able to use more blunt teeth. As 

 they wear down, the mark, which was at first narrow and as 

 long as the size of the tooth would allow, becomes short, wide, 

 and shallow, and at the age of eighteen months the mark in 

 the front pair will have become much shorter and more indis- 



