WUAT MAY PUZZLE A S'OyiCE. 205 



At two years and a half the centrals are shed ; the 

 marks are faint in the dividers, but are distinct in the 

 corners. 



At three years the permanent centrals are nearly 

 grown ; the marks in the dividers are just visible, and 

 have become smaller in the corners. 



At three years and a half the marks in the centrals 

 are long and very distinct; the dividers are shed, and 

 the marks in the corners are faint. 



At four years tlie marks in the centrals show the 

 effects of wear, but are still long and distinct ; the per- 

 manent dividers are about grown, and tlie marks in 

 the corner teeth have almost disappeared. 



At four years and a half the marks in the centrals 

 are still distinct, wiiile those of the dividers are at 

 their best. The contrast between the large permanent 

 incisors and the small temporary corner teeth, which 

 have lost their marks, is striking at this age. 



At five years the marks in the centrals are getting 

 smaller and rounder, bnt are large and distinct in the 

 dividers ; the corners are usually shed at this age. 



"At six years," says Prof. Youatt, "the marks of 

 the central nippers are worn out. There will, however, 

 still be a difference of color in the center of the tooth. 

 The cement filling the hole made by the dipping of 

 the enamel will present a browner hue than the other 

 part of the tooth. It will be distinctly surrounded by 

 an edge of enamel, and there will remain even a little 

 depression in the center, and also around the case of 

 enamel ; but the deep holes in the center of the teeth, 

 with the blackened surface which they present, and 

 also the elevated edge of enamel, will have disappeared. 

 Persons little accustomed to horses are often puzzled 

 here. They expect to find a plain surface of uniform 



