ANIMAL DENTISTRY. 105 



Ten to twelve years — The inferior centrals and laterals 

 are more triangular, the cups of the inferior corners are 

 disappearing entirely, the enamel around the infundibula 

 of the centrals and laterals is changing from oblong to round, 

 the crusta petrosa groove on the superior corners is two 

 to three millimeters long and is appearing on the laterals 

 and centrals, and finally the length of the crowns of the 

 superior incisors is markedly increased. The crowns of the 

 canines are large and are becoming rounded at the gingival 

 margin. The inclination of the incisor arcades is now a 

 marked feature of the mouth and is recognized by a mere 

 glance at the lateral aspect of the arcades. (Figs. 74, 75, 76.) 



Thirteen to fifteen years — The crusta petrosa groove on 

 the superior corner incisor is nearing the middle of the 

 crown, the tables are markedly triangular, the crowns of 

 the superior incisors are becoming widely separated from 

 the gums, and are becoming narrow near the gingival mar- 

 gin, the infundibula of the central and lateral inferior in- 

 cisors are now but small circles of enamel — the enamel 

 island — projecting above the level of the dentine and located 

 well toward the posterior aspect of the table, and the gingi- 

 val margin of the superior central incisors is much lower 

 than that of the laterals. The crowns of the canines are 

 round at the gingival margin (Fig. Tj.) 



Sixteen to twenty years — The inclination of the incisor 

 arcades is so pronounced that the inferior incisors pro- 

 ject forward almost on a straight line with the jaw, the 

 superior corner incisor is grooved almost to the contact 

 border, the crusta petrosa grooves extend well downward 

 over the crowns of all the incisors, the crown of the cen- 

 trals is shorter than that of the laterals, the infundibula have 

 either disappeared entirely or exist only in the form of 

 small projections of enamel near the posterior border of the 

 tables of the inferior incisors, the crowns of all the superior 



