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VETERIJSTABY MEDICINE AND SURGERY. 



The gradual effect of wear in producing this alteration is shown in 

 Figure 152 where successive portions of the upper surface of the tooth are 

 represented as having been removed by the saw. The original form of 

 the tooth is shown in Fig. 153. 



Fig. 153. 

 Original Form of a Tooth. 



The amount of wear on the upper surface of the teeth is greater in 

 the young mouth than it is afterwards, because in youth the teeth meet 

 more fairly than they do in after years. Compare Fig. 165 and Fig. 

 163. The rate of wear gradually decreases, as years increase, because 

 the teeth do not meet so directly, but on the contrary project more and 

 more forward in something like two parallel lines. For example a quarter 

 of an inch will usually be worn off the surface between five and six years 

 old, whilst, probably not more than that quantity will be worn off between 

 twenty and twenty-five years old. 



Triangularity. — A further very well-marked indication of increasing 

 age is given by increasing depth from front to rear in the upper surfaces 

 or crowns of the teeth. This increase of depth will be noticed if Figs. 145 

 and 146 are carefully compared with Figs. 142, 143, and 144. Further 

 wear causes the crowns of the teeth to assume a triangular form. The 

 cause of this will be clearly seen on reference to Fig. 152. The teeth, 

 though they diminish in lateral breadth, increase in thickness from front 

 to rear all the way from the crown to the fang. Figs. 152 and 153. 



At six and up to eight years old, the teeth are all broad laterally at 

 their upper surfaces. Figs. 144, 145, and 146. Up to this time the exact 

 year, as the reader will recollect, is pretty well known by the ''marks." 



