ERUPTION OF THE PERMANENT TEETH. 



201 



tubercles and the wearing of the enamel from these. As we 

 have just seen, the leveling commences with the inferior pinchers, 

 is followed by that of the inferior intermediate teeth, and does 

 not commence on the superior incisors until it is complete on 

 the inferior ones ; with the superior incisors it commences with 

 the pinchers and follows with the intermediate teeth ; the tusks 

 do not commence to wear until the use of the incisors is marked. 

 The leveling of the teeth may, however, take place much more 

 rapidly or more slowly than has been indicated above, and may 

 even be very irregular in the teeth which it first affects, accord- 

 ing to the nature of the food upon which the animal is 

 nourished. 



Fig. 184. 



Fig. 185. 



Teeth of do^ over three vears old, showing Teeth of an old dog ; all of the incisors and 

 use of all of the incisors ; the tushes are be- tushes are much used and worn, 



coming yellow, 



Doo's fed on meat and those which have bones to knaw 

 use their teeth more rapidly than those which are fed on 

 soups, broken bread, and vegetables. Dogs which are y)ugna- 

 cious, and those which are taught to swing on ropes or straps 

 and to fetch objects, such as sticks, stones, etc., use their teeth 

 rapidly and are apt to have their tusks much worn. These dogs 

 also frequently have irregular mouths, from broken teeth. From 

 these causes it sometimes happens, especially with the larger 

 dogs, that the teeth are so altered after three years that no 

 intelligible deduction can be drawn from the appearance of 

 the mouth. 



