SUCCESSION OF THE TEETH. 



63 



most level, and the corner ones are becoming so. Tlie mark in 

 the two middle teeth is wide and faint, in the two next teeth it 

 is longer, darker and narrower. In the rig. 3. 



corner teeth it is longest, darkest and nar- 

 rowest. 



" 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 par- 

 ticulars connected with them. The foal 

 is born with two grinders in each jaw, 

 above and below, or they appear within 

 two or three days after the birth. Before the expiration of the 

 month they are succeeded by a third, more backward. The 

 crowns of the grinders are entirely covered with enamel on the 

 tops 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 in grinding 

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

 made an additional provision for their strength and endurance. 

 Fig. 4 represents a grinder sawed across. The live dark spots 

 rej)resent bony matter ; the parts covered with lines enamel, 

 and the white spaces a strong bony cement uniting the other 

 portions of the teeth. 



" At the completion of the first year a fourth grinder usually 



soon afterwards, six 



Fis. 4. 



( 

 ^f^^ 



comes up, and the yearling has then, or 

 nippers and four grinders above and below 

 in each jaw, which, with the alteration in 

 the nippers we have just described, will 

 enable us to calculate the age of the foal, 

 subject to some variations arising from the 

 period of weaning, and the nature of the 

 food. 



" At the age of one year and a half, the mark in the central 

 nippers will be much shorter and fainter ; that in the two other 

 pairs will have undergone an evident change, and all the nip- 

 pers will be flat. At two years this will be more manifest. 

 The accompanying cut, Fig. 5, deserves attention, as giving an 



