Thompson, Cells in the Cerebral Cortex of Man. 127 



ter method is the one adopted. Take the frontal lobe for an 

 example. To each of its eight regions is assigned a value 

 which represents its size relatively to the others, and which has 

 been called the value of the region (vide Tables II and III), 

 The unit column, or more accurately, 100 times the unit col- 

 umn (or the number of cells per square mm. of area), is multi- 

 plied by the value of its region, giving the weighted numbers 

 of cells per column one square millimeter in section. The sum 

 of the weighted numbers per (square millimeter) column of 

 all of the regions composing the lobe is then divided by the 

 sum of all their values, and this quotient is the average number 

 of cells per (square millimeter) column for the frontal lobe. 

 The calculation of the average number of cells per (square mil- 

 limeter) column for each lobe is given in Table II. 



TABLE II. 

 The Average Number of Cells per Square Millimeter in the Cortex 



OF Each Lobe. 



But the averages in Table II apply to the exposed surfaces 

 of the lobes only. To obtain the average for the sunken sur- 

 faces also, an average percentage reduction for each lobe is first 

 found. The method employed in obtaining this average is the 

 same as that described in the preceding paragraph. The per- 

 centage for each region is weighted by the value of the region 

 and the sum of the weighted percentage divided by the sum of 

 the values. The quotient is the percentage reduction for the 

 entire lobe (Table III). 



