THE TEETH. 



203 



The six-year-old mouth is the last upon which any great 

 lelianee can be placed, if it is desired to ascertain the age of the 

 horse to a nicety; but by attentively studying both jaws, a near 

 approximation to the truth may be arrived at. It is ascertained 

 that the nippers of the upper jaw take about two years longer to 

 wear out than those of the lower; so that until the horse is eight 

 years old, his age may be ascertained by referring to them, nearly 

 as well as by the lower nippers at six. But as different horses 

 wear out their teeth with varying rapidity, it is found that this 

 test cannot be implicitly relied on; and in crib-biters or wind- 

 suckers the upper teeth wear out wonderfully soon. Fig. 7 is 

 taken from the lower jaw of a six-year-old horse, showing the marks 

 of the central nippers almost obliterated, but still presenting con- 

 centric circles, of discolored brown tartar in the middle ; next to 

 which is the cement, then the enamel, and the dentine, with a thin 

 layer of enamel outside. Up to this age, the nippers stand nearly 

 perpendicular to each other, the two sets presenting a slight con- 

 vexity when viewed together, as seen in figure on p. 254. After- 

 wards the nippers gradually extend themselves in a straight line 

 from each jaw, and, in the very old horse, form an acute angle 

 between them. 



Pig. S. — UPPER MPPiJis in the kk.ht i> \r-old hokse. 



A. Anterior maxillary bone. 



1. 1. Central nippers, worn to a plane 



surface. 



2. 2. Next pair, still showing a slight 



remnant of the cavity. 



3. .3. Corner nipi>ers, showing the marh 



l^ilainly enough. 



4. 4. Tushes, more worn down than in 



the lower jaw of the six-year-old 

 mouth. 



At about the eighth year, the upper nippers present the 



