16 General Remarks on Nerve Cell Lamination [CHAP. 



They lie on a level with that part of the supraradiary layer in which the plexus of 

 fibres begins to show an increase in wealth. 



Layer of Medium-Sized Pyramidal Cells. 



Many authors do not approve of this subdivision. But in almost any part of the cortex, 

 on descending from the layer of small pyramidal cells, an increase in size and a widening 

 of the interval between the individual elements become plainly visible, and the reverse, when 

 we ascend from the subjacent layer; hence it seems justifiable to grant independence to 

 the lamina. Being a very equally represented and constant layer it cannot be made much 

 use of in forming judgment on topographical variations. Also, as its boundaries are elastic 

 it cannot be satisfactorily measured, but it is considerably deeper than the overlying layer 

 of small pyramidal cells. The constituent cells show a progressive increase in diameter from 

 above downwards, but they invariably preserve a uniform elongated pyramidal shape. 



The regional variations presented by this layer are unimportant and it corresponds with 

 the supraradiary layer of nerve fibres. 



External Layer of Large Pyramidal Cells. 



Meynert and others have included this with the foregoing lamina, and distinguished 

 the combination by the term " third layer," but to this I strongly object. True it is that 

 these cells bear a morphological resemblance to those above, but no one will deny that the 

 volumetric augmentation occurs rapidly, nor will it be contended that the increase in bulk 

 is not attended by an equally sudden accession of chroinophihc elements (Nissl bodies). 

 Moreover, the alterations in size and to a less extent the variations in shape, exhibited 

 by these cells, constitute one of our most important criteria in dividing the brain surface 

 into different histological territories. But these are points which will be dilated upon when 

 these areas are discussed ; for the moment, let it suffice that there are strong reasons for 

 placing the lamina on a separate standing. 



The fact that these cells lie on a level with the line of Baillarger and the dense 

 lower part of the interradiary plexus goes to show that they contribute in no small 

 measure to the fibre density of this level, and strengthens the plea for their independent 

 consideration. It might be also noted here, that in those situations where the line of 

 Baillarger is reduplicated, the inner streak coincides with a well-developed internal layer 

 of large pyramidal cells. 



Layer of Stellate Cells. 



Known also as the fourth layer, the granule layer or Kornerschicht (in Germany), this 

 is another valuable guide to the delineation of histological subdivisions, because it is subject 

 to very remarkable variations in representation. In regions where it is well-developed it 

 stands out plainly under a low microscopic power, in the form of a streak, situated a little 

 more than half-way down the cortex ; on further magnification, it is found to consist of 

 closely packed, minute (5 by 8 /it), polymorphous elements, mingled with which a few small 

 pyramidal cells arrest attention. Curiously enough this lamina is best represented in the 

 calcarine cortex, and there lies in association with the accentuated line of Baillarger (Gennari). 

 This observation caused me to start originally with the belief that the layer of stellate 

 cells corresponded in position with the line of Baillarger, and that the two were mutually 

 interdependent. But this was soon proved to be a fallacy, and we now know that if 



