134 Journal of Comparative Neurology. 



centages for the separate regions are averaged to obtain a per- 

 centage for the entire cortex, was explained in III, A. Table 

 VI gives the final outcome of the calculation on volume, which 

 is that only 1.37% of the total volume of the cortex is com- 

 posed of functional nerve cell bodies. 



IV. A Calculation of the Total Number of Giant Cells 

 IN the ,Cerebral Cortex of Man, and a Compar- 

 ison of the Number of Giant Cells with 

 the Number of Pyramidal Fibers 

 Passing to the Spinal Cord. 



A. From the time the giant cells of the Rolandic region 

 were described by Betz,^ they have been regarded as distinct- 

 ively motor cells, and it has been supposed that they gave rise 

 to some at least of the fibers of the pyramidal tracts. We are 

 now in a position to test the numerical relationship between 

 giant cells and pyramidal fibers, and discover whether we can 

 regard the giant cells as the origin of all the pyramidal fibers, 

 or of only some of them. 



The data used in the preceeding calculation furnish a basis 

 for computing the total number of giant cells in the cortex. 

 Only three regions contain giant cells, regions 5, 6 and 7. In 

 each region the cells are given a frequency of 10 to the square 

 mm. But they occur only in 4% of region 5, and in 2% of 

 region 6. The total area of the frontal lobe was given as 96,- 

 432 sq. mm. Region 5 comprises 12% of the entire lobe; 

 region 6, 4%, and region 7, 16%. The cortical area in which 

 giant cells appear, is therefore 462.8 sq. mm, in region 5 ; 77. i 

 sq. mm. in region 6, and 15,429.1 sq. mm. in region 7, giving 

 a total cortical area of 15,969 sq. mm., in which giant cells are 

 present. Since the distribution of the giant cells is 10 per 

 square milHmeter (II B) there are 159,690 giant cells in the en- 

 tire cortex. 



' Loc. cit. p. 580. 



