Thompson, Cells in tfie Cerebral Cortex of Man. 125 



ticularly the lower portion, is the center for some or all of the 

 skin and muscle senses. Region 8 has therefore been placed 

 with the sensory centers. 



A comparison of the number of cells in the unit columns 

 of the three different functional regions, shows a certain uni- 

 formity among the unit columns for each region. The motor 

 regions have the smallest number of cells on an average, and the 

 sensory the largest, while the association regions range between 

 the two. The two extreme exceptions to this generalization, 

 regions 15 and 16, the gyrus fornicatus and the island, are dis- 

 tinctly modified portions of the cortex, which are not typical 

 of the great association regions, and perhaps are not fairly to 

 be classed with them. 



D. The plates accompanying the monograph furnish an 

 opportunity for a confirmation of the calculations of the num- 

 ber of cells in the unit columns. Sections from nine different 

 regions are represented, enlarged 200 diameters. The thickness 

 of each section is given as 20/<. By counting the number of 

 in an area 20 mm. wide (o. i mm, of the original section) and 

 as long as the entire thickness of the cortex, and multiplying 

 this number by five (since the sections shown are 20 ;< thick), 

 the number of cells in the unit column can be found. The 

 numbers thus obtained by counting the cells in the lithographed 

 plates, tally very closely with those calculated from the data 

 given in the text. 



E. The data upon which the estimates for the unit columns 

 are based, do not apply to the entire cortex of the regions 

 which they represent. They are in each case, the numbers for 

 the unit columns in the siimmiis of the gyri, and do not apply 

 to the cortex covering the sides and bottom of the sulci. Since 

 the exposed portions of the cortex comprise in all only about 

 one third of the entire area,^ it is necessary to determine also 

 the unit columns for the other two-thirds, the sunken portions. 

 Hammarberg does not give exact figures for these, but he tells 



' Wagner, H. Maasbestimmungen der Oberflache des grossen Gehirns. 

 Inaug. Diss. GSttingen, 1864. 



