628 E. H. J. SCHUSTER. 



The prefrontal t3"pe (differs from the frontal in its compara- 

 tive poverty in cells and in the smaller size of the cells of 

 layers iii h and v, particularly tlie former. Its depth is also 

 less. Measurements of the cells in the two layers mentioned 

 were made near the posterior boundary of the frontal region 

 and in the prefrontal. It was found that in the former 

 position tlie largest cells at iii h were about 40 fx in length x 

 30 ju in breadthj while in the latter 80 |U x 23 /u represents 

 approximately their dimensions. 'The general average is, 

 however, in each case much less. The corresponding figures 

 for layer v are : in posterior part of the frontal area about the 

 same as for layer iii h, while in the prefrontal area, 35 /x x 

 27 /t roughly indicates their size. In fig. 3, which is taken 

 fairl}^ far forward in the frontal region, it will be noticed that 

 the subgranular pyramids are rather larger than those 

 situated above the granules, and that the cells of each layer 

 are slightly larger than the corresponding cells in fig. 4. 



The extent of the lamina multiformis and the shape of its 

 cells depend to a great extent to the prevalent direction of 

 the fibres of the underlying white matter; where this is 

 tangential the layer is shallow and its cells tend to be drawn 

 out tangentially ; where the fibres radiate upwards towards 

 the surface the cells are elongated along an axis vei'tical to 

 the surface, and the layer tends to be deep. This effect of 

 the direction of the fibres is not always confined to the lamina 

 multiformis, but the layers lying above it may all be involved. 

 It is not confined to one part of the hemisphere, but mny be 

 noted in all. It is mentioned hei'o because, in the pai't of the 

 prefrontal region figured, the fibres are arranged tangentially, 

 while in fig. 3 they ai-e radial in direction. It seemed desii- 

 able to explain that this difference is not an essential difference 

 between the two types. In the region of the frontal })olethe 

 direction of the fibres of the prefrontal cortex is I'adial, and 

 the result is a marked difference of appearance in the shape 

 and arrangement of the cells, particularly of the lower layei-s. 

 The condition described by Brodmann as type 12 may thus 

 be distinguished : " slender pyramids," " layer vi much 



