THE UNCERTAIN PERIOD. 



85 



four of the permanent central incisors are seen. After 

 this the other milk-teeth decrease rapidly, but are slow 

 to disappear ; and at three years old the third pair of 

 permanent teeth are but formed, as in Fig. 25 ; and at 

 four years the last pair of incisors will be up, as in 

 Fig. 26 ; but the outside ones are not yet fully grown, 



Fig. 25. Three years past. 



Fig. 26. Four years past 



and the beast can hardly be said to be full-mouthed till 

 the age of five years. But before this age, or at the age 

 of four years, the two inner pairs of permanent teeth 

 are beginning to wear at the edges, as shown in Fig. 

 26, while at five years old the whole set becomes some- 

 what worn down at the top, and on the two centre ones 

 a darker line appears in the middle, along a line of 

 harder bone, as appears in Fig. 27. 



Now will come a year or two, and sometimes three, 

 when the teeth do not so clearly indicate the exact age, 

 and the judgment must be guided by the extent to 

 which the dark middle lines are worn. This will de- 

 pend somewhat upon the exposure and feeding of the 

 animal ; but at seven years these lines extend over 

 all the teeth. At eight years another change begins, 

 8 



