ERUPTION OF THE PERMANENT INCISORS. 



165 



rior borders at six months and are leveled at ten months ; the 

 arch is broken in the centre and loses its continuity at the 

 first intermediate at one year, second intermediate at fifteen 

 months, and at the corner teeth at eighteen to twenty months. 



Fig. 162. 

 Two years, a, external face, b, internal face. 



THIRD PERIOD ERUPTION OF THE PERMANENT INCISORS. 



Twenty Months. — At this time the milk-pinchers are re- 

 placed by the permanent ones, which protrude somewhat 

 obliquely, but soon assume their natural position and are in 

 place at two years. (Fig. 162.) 



