Thompson, Cells in the Cerebral Cortex of Man. 1 2 1 



cells in a unit cube o. i mm. on a side. Now the entire cortex 

 may be regarded as made up of square columns, whose cross 

 section is o. i mm. square, and whose height is, in each case, 

 equal to the thickness of the cortex in the region in which it 

 belongs. Each of these unit columns may be considered as 

 made up of cubes o. i mm. on a side, piled upon one another. 

 All the columns for any one region must be regarded as ident- 

 ical in structure, since a single set of measurements serves for 

 them all. Since the thickness of each layer is given, the num- 

 ber of unit cubes which belong in any given layer of a unit 

 column can be easily determined. The number of cells in the 

 unit cube is given immediately. A simple multiplication of 

 these two factors, the number of unit cubes in a layer by the 

 number of cells in the unit cube, gives the total number of cells 

 in any layer of the unit columns. To take a concrete instance, 

 the third layer in region i is o. 5 mm. thick and the frequency of 

 the cells for the layer is 15. (Vide Table VII.) Since the layer 

 is o. 5 mm., thick, it must contain 5 of the unit cubes (o. i mm.)*. 

 Each unit cube contains 15 cells, therefore the total num- 

 ber of cells for the third layer of the unit column is 5 x 15, or 

 75. By going through with the same operation for each of the 

 other layers, and then summing the results, the total number 

 of cells in the unit column of region i is easily obtained. The 

 number of cells in the unit columns of each of the fifteen re- 

 gions considered, was calculated in this way. 



B. Beside the cells uniform in size included in the fre- 

 quency number for the layer, the third, fourth and fifth layers 

 in many places contain scattered large pyramidal cells. In the 

 motor regions, these are larger than elsewhere in the cortex. 

 They appear in the fifth, or ganglion cell layer, and are the so- 

 called giant cells. Hammarberg says nothing that would fur- 

 nish a basis for an estimate of the frequency of these extra 

 large cells. The distribution of the giant cells was therefore 

 adopted as typical of these scattered large pyramidal cells wher- 

 ever they occur and the average distance between giant cells 

 determined by measurement of the laboratory sections of motor 

 cortex. By this means, it was found that an allowance of 10 



