AGE BY THE TEETH. 97 



permanent full mouth the centrals, having been in wear for the long- 

 est period of time, show the shallowest cups, while in the 3-year-olcl 

 mouth the new centrals, having been in wear for the shortest period 

 of time, show the largest, deepest, and blackest ones. The colt is 

 said to be 3 years past when the permanent centrals show wear on 

 both their front and rear borders. At about the age of 3^ years the 

 temporaiy laterals are shed, and until their permanent successora 

 are up and in wear the colt is rising 4. 



At 4 the colt has four permanent incisors (the centrals and later- 

 als) and two temporary ones (the corners) in each jaw. The laterals 

 are worn on both their front and rear borders, and the cups of the 

 lower centrals, having been in wear for one year and being about one- 

 third gone, show smaller than the cups of the laterals. At this age 

 the contrast between the large permanent incisors and the small 

 temporary corners is very striking. The colt is about 4^ years old 

 when the corners begin to shed. At about this time the mouth of 

 the male begins to show the tushes. After the temporary comers 

 have all been shed, and until the four permanent comers are in con- 

 tact, the colt is rising 5. 



At 5 the mouth is full. All the incisors are now permanent, and 

 in each jaw they have all reached the same level. The front borders 

 of the comers are in wear but the rear borders are not yet up. The 

 cups of the centrals, having been in wear for two years, are about 

 two-thirds gone, while those of the laterals, having been in wear for 

 one year, are about one-third gone. Usually the rear borders of the 

 comers come up and inHlie wear while the animal is between 5 and 

 6 years old, but sometimes they do not come up as they should, and 

 such a condition constitutes what is known as a shell mouth. This 

 condition may cause an 8-year-old animal to be mistaken for a 6- 

 year-old. 



At 6 the cup cavities are worn entirely out of the centrals, two- 

 thirds out of the laterals, and one-third out of the corners. At 6 

 past, a notch begins to foxni. on the outer border of the upper corners. 



At 7 the cups are gone from the centrals and the laterals, and the 

 notch which began forming at 6 past on the-upper comers is now well 

 marked. The enamel is now beginning to lose its cement covering, 

 with the result that the teeth are showing whiter than they did when 

 the animal was 6. The tables of the centrals are becoming oval in 

 form. 



At 8 the blackened cups have usually disappeared from all of the 

 lower incisors, although in some cases those of the comers persist for 

 a year or two longer. The notch in the upper comers is hardly as 

 prominent at this age as it was at 7 because, on accoimt <5f wear, the 

 angle of meeting is now beginning to change, and the upper corners in 



