THE TEETH 



423 



upper and lower incisors have replaced the corresponding milk teeth ; 

 in the skull of another kitten of the same litter, one hundred and 

 twenty days old, all the permanent incisors have appeared. It may 



FIG. 345. 



ERUPTION OF PERMANENT FIRST UPPER INCISOR TOOTH, 

 AND LOSS OF DECIDUOUS FIRST LOWER INCISOR. 



be safe, therefore, to assume that the date for the eruption of the first 

 permanent tooth is near the end of the fourteenth week after birth. 

 The first permanent tooth to appear is the first, or internal, upper 



FIG. 346. 



ERUPTION OF PERMANENT SECOND UPPER INCISOR TOOTH ; 

 PERMANENT FIRST UPPER INCISOR IN POSITION; PER- 

 MANENT FIRST AND SECOND LOWER INCISORS PUSHING 

 OUT CORRESPONDING DECIDUOUS TEETH. 



incisor (Fig. 344). In some cases an interval of time may elapse 

 between the loss of a tooth and the appearance of its successor ; thus 

 in one specimen examined (Fig. 345) the first lower incisor was lost 

 while the first upper incisor was coming down. As a rule, however, 



