122 



PROCESS OF TEETHING. 



The 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 gath- 

 ering up the animal's food, and in such employment 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 ini 

 them. The inside and bottom of this pit being blackened by| 

 the food, constitutes the mark of the teeth, by the gradual dis- 

 appearance 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 hol- 

 low towards the mouth, and present at first a cutting surface, 

 with the outer edge rising in a slanting direction above the inner 

 edo-e. This, however, soon begms to wear down until both sur- 

 faces are level, and the mark, which was originally long anil 

 narrow, becomes shorter, and widei, 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 nar- 

 rower ; 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 ea- 

 sily inspect them ; but there are some 

 interesting particulars connected with 

 them. The foal is born with two 

 grinders in each jaw, above and be- 

 low ; or they appear within three or 

 four days after the birth. Before the 

 expiration of a month they are suc- 

 ceeded by a third, more backward. 

 The crowns of the grmders are entirely covered with enamel on 

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

 and there remains a compound surface of alternate layers of 

 crusted petraser, enamel, and ivory, which are employed iji 

 grinding down the hardest portion of the food. Nature has, 

 therefore, made an additional provision for their strength and 

 endurance. 



Fia:. 16. 



