ANIMAL DENTISTRY. 89 



FROM FIVE TO EIGHT YEARS. 



The age during this period is determined by changes in 

 the infundibula of the inferior incisors, the cups of which 

 disappear in regular succession, beginning with the centrals. 

 In some instances a small round spot remains for several 

 years in the center of the infundibulum, but this event must 

 be regarded as equivalent to the disappearance. The disap- 

 pearance of the blackened cup is marked by the appearance 

 of the crusta petrosa filling the bottom of the infundibulum. 

 At six years old the central cup disappears, at seven the 

 lateral cup. and at eight the corner one has become shallow 

 and rounded. The cup of the corner inferior incisor is more 

 persistent than that of the centrals and laterals, and may 

 remain quite prominent even at the age of ten to eleven 

 years. Its change in shape from elliptical to round is equal- 

 ly valuable in the determination of the age at that period. 



FROM NINE YEARS TO OLD AGE. 



After the age of nine years the retrogressive changes 

 continue incessantly, but without any prominent event to 

 mark the exact age. The age of the horse is henceforth 

 only estimated. 



Nine years — The age of nine years is easily determined 

 by the appearance of the crusta petrosa groove at the gingi- 

 val margin of the superior corner incisor and the slight 

 downward curvature of the gums at that point. The infun- 

 dibula of the inferior incisors are nearer to the posterior bor- 

 der of the taldes of the centrals, which are now quite 

 triangular. The inferior corner incisors are still oblong, 

 present a rounded black cup and are beginning to show the 

 first sign of increased inclination of the incisor arcades. The 

 anterior surfaces of the teeth are becoming yellow. 



