'Normal" range of variation. 



PLATE 27 



: i It 



s 



z 



> 



- n -: 



1 > to 



= t 



n > O 



= - u 



u .- -: 



a > 



o 3 



- - 



_ - 



S s:' m 



n > Z 



a 2 . 



m 

 n 



z 

 z 



