THE PROCESS OP TEETHING. 195 



which have now considerably grown, but not attained their perfect height. 

 This cut will represent the appearance of the mouth 

 at that time. 



At two months, the central nippers will have reached 

 their natural level, and between the second and third 

 month the second pair will have overtaken them. 

 They will then begin to wear away a little, and the 

 outer edge, which was at first somewhat raised and 

 sharp, is brought to a level with the inner one, and 

 so the mouth continues until some time between the 

 sixth and ninth month, when another nipper begins to 

 appear on each side of the two first, making six above 

 and below, and completing the colt's mouth ; after 

 which, the only observable difference, until between 

 the second and third year, is in the wear of these teeth. 



The term nipper is familiar to the horseman and the farrier, and much 

 better expresses the action of these teeth than the word incisor or cutter, which 

 is adopted by anatomists. Whoever has observed a horse in the act of brows- 

 ing, and the twitch of the head which accompanies the separation of each 

 portion of grass, will perceive that it is nipped or torn rather than cut off. 



These teeth are covered with a polished and exceedingly hard substance, 

 called the enamel. It spreads over that portion of the teeth which appears 

 above the gum, and not only so, but as they are to be so much employed 

 in nipping the grass, and gathering up the animal's food, and in such employ- 

 ment even this hard substance must be gradually worn away, a portion of 

 it, as it passes over the upper surface of the teeth, is bent inward, and sunk 

 into the body of the teeth, and forms a little pit in them. The inside and 

 bottom of this pit being blackened by the food, constitutes the mark of the 

 teeth, by the gradual disappearance of which, in consequence of the wearing 

 down of the edge, we are enabled, for several years, to judge of the age of the 

 animal. 



The colt's nipping teeth are rounded in front, 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 

 nippers are beginning to wear to a level. The annexed cut will convey some 

 idea of the appearance of the teeth at twelve months. The four middle 

 teeth are almost level, and the corner ones becoming so. The mark in the 

 two middle teeth is wide and faint ; in the two next 

 teeth it is darker, and longer, and narrower ; and 

 in the corner teeth it is darkest, and longest, and 

 narrowest. 



The back teeth, or grinders, will not guide us 

 far in ascertaining the age of the animal, for we 

 cannot easily inspect them; but there are some 

 interesting particulars connected with them. The 

 foal is bom with two grinders in each jaw, above 

 and below ; or they appear within three or four 

 days after the birth. Before the expiration of a 

 month they are succeeded by a third, more back- 

 The crowns of the grinders are entirely covered with enamel on the 



ward. 



top and sides, but attrition soon wears it away from the top, and there remains 

 a compound suiface of alternate layers of crusted petraser, enamel, and ivory, 



o 2 



