132 



Journal of Comparative Neurology, 



TABLE VI. 



The Average Percentage of the Total Volume of the Cerebral Cortex 

 Composed of Functional Nerve Cell Bodies. 



average cL 

 for cortex 



1-37/0 



B. The only portion of this process which needs detailed 

 explanation is the method of obtaining the sum of the volume 

 of all the cells in each unit column. Hammarberg gives two 

 measurements for the typical cell of each layer, the long and 

 the short diameter, in micra (Table VIII). Since almost all the 

 cells are pyramidal in shape, the volume of each cell was calcu- 

 lated according to the formula for the cone ; one third of the 

 area of the base multiplied by the altitude. The short diameter 

 was of course taken as the diameter of the base of the cone, 

 and the long diameter as its altitude. The justification for the 

 use of the formula for the cone is perhaps not evident at first 

 sight. If the triangle which represents the projection of a cone 

 is circumscribed about the drawing of a pyramidal cell, using 

 the widest portion of the cell body as the base of the cone, it 

 is at once evident that not all the triangle is filled. The 

 cell walls, instead of following a straight line from base to apex, 

 sag in and leave part of the space unoccupied. But on the 

 other hand, the outline of the cell is not all contained within 

 the projection of the cone. The bottom of the cell is not flat 

 like a cone, but it rounds down from its widest point. Beside 

 this there are a number of dendritic processes which are to be 

 included with the cell body, but are not contained within the 

 circumscribed cone of the drawing. Moreover when the cell is 

 thought of, not as projected in a drawing, but as it exists in 

 space, it is evident that the basal outline of the cell would not 

 be a perfect circle like that of the cone, but an irregular figure 

 which would sag away from the circle at some points and pass 



