424 



MAMMALIAN ANATOMY 



the deciduous incisors are pushed out by the permanent teeth which 

 erupt behind them. 



FIG. 347. 



ERUPTION OF PERMANENT THIRD LOWER INCISOR AND 

 LOWER MOLAR TEETH; PERMANENT FIRST AND SECOND 

 TIPPER AND LOWER INCISORS IN POSITION. 



The second upper incisor appears shortly after the first ; at about 

 the same time the permanent first and second lower incisors push out 

 the corresponding milk teeth (Fig. 346). 



The third lower incisor now pushes out the deciduous tooth, and 



the posterior part of the permanent lower molar rises through the gum 



(Fig. 347). If the gum be cut away at this stage, in some specimens the 



permanent upper molar and the point of the first premolar will be visible. 



The third upper incisor appears next, and at about the same time also 



the small first upper premolar 



FIG. 348. (Fig. 348). At this stage after 



the gum has been removed the 

 permanent canines are visible. 



After the permanent upper 

 canine has descended for some 

 distance in front of the decidu- 

 ous canine, and after the per- 

 manent molar is in position, the 

 second and third upper pre- 

 molars begin to push out the 

 second and third milk molars 

 (Fig. 349). The second pre- 

 molar appears in the interval between the anterior and internal 

 fangs of the deciduous sectorial. The principal cusp of the permanent 



ERUPTION OF PERMANENT THIRD UPPER INCI- 

 SOR AND FIRST UPPER PREMOLAR TEETH, FIRST 

 AND SECOND PERMANENT UPPER INCISORS 

 IN POSITION ; IN SKULL ONE HUNDRED AND 

 TWENTY DAYS AFTER BIRTH. 



