74 ANIMAL DENTISTRY. 



have a longer exposed portion (crown) in the aged subject, 

 owing to the receding of the alveolar margin. 



A SUMMARY OF DENTAL EVOLUTION AND RET- 

 ROGRESSION APPLIED TO THE DE- 

 TERMINATION OF AGE. 



The age of the horse is determined by the examination 

 of the incisor teeth, and in certain instances the molars, as 

 follows : 



(i) From birth to one year by the evolution of the 

 temporary incisors. 



(2) From one year to two and a half years by the 



eruption of the fourth and fifth molars and 

 the evolution of the temporary incisors. 



(3) From two and one-half years to five years by 



the retrogression of the temporary incisors, 

 the evolution of the canines and the evolu- 

 tion of the sixth molar. 



(4) From five and a half years to nine years by the 



retrogression of the infundibula of the in- 

 ferior incisors. 



(5) From nine years to old age by : 



(i) Changes in the shape of the tables of the in- 

 ferior incisors. 



(2) Changes in the anterior face of the superior 



incisor arcades. 



(3) Changes in the inclination of the incisor ar- 



cades. 



(4) Changes in the crown of the canines. 



(5) Changes in the molars. 



FROM BIRTH TO ONE YEAR. 



The colt at birth, or within a day or two after, has four 

 incisor teeth — the superior and inferior nippers, and three 



