n] General R<'iimrl>* <m .Vow Cell Luinint!<m 15 



GENERAL REMARKS ox CELL LAMINATION. 



It is not for me to enter upon a historical narrative telling of studies on cell-lamina- 

 tion, nor to criticise the classifications suggested by Kolliker, Remak, Berlin, Arndt, Meynert, 

 Betz, Bevan Lewis, Baillarger, Golgi, Schwalbe, and others whose names are equally familiar, 

 because that has already formed a theme for the abler pens of Hammarberg and Ramon y 

 Cajal. It is, however, of the greatest importance that there shall be no misunderstanding 

 concerning the different laminae of which I shall write hereafter, and that the classification 

 I propose to follow shall be plainly indicated. Hence for purposes of identification more 

 than anything else, I give the following brief explanatory description, in which histological 

 details are avoided, in order that points of interest from the localisation standpoint may be 

 emphasised. Also, it will clear the ground if I incidentally and summarily point out what 

 layers, in sections stained for nerve fibres, correspond with the various cell-laminae. 



The following is the classification and nomenclature to which I propose to adhere, and 

 the lamination is one which is recognisable or definable over almost the entire cortex, the 

 visual and olfactory areas being variants. 



Plexiform Layer. 



Layer of Small Pyramidal Cells. 



Layer of Medium-Sized Pyramidal Cells. 



External Layer of Large Pyramidal Cells. 



Layer of Stellate Cells. 



Internal Layer of Large Pyramidal Cells. 



Layer of Spindle-Shaped Cells. 



From the above it may be gathered that the thin superficial coat corresponding with 

 the outermost fibreless layer will not be taken into account. It has little cytological interest 

 and is chiefly composed of a fine neuroglial network. 



Plexiform. Layer. 



The term " plexiform " is borrowed from Ramon y Cajal. The layer is equally well-known 

 as the " molecular " or " first layer." As its cell constituents are small and sparsely-scattered 

 and not displayed to advantage in Nissl specimens, it possesses little value for the student 

 of localisation, and even the variations in depth which it exhibits have to be viewed with 

 caution, for not only do these alter in different parts of one gyrus, but measurements are 

 falsified by the least obliquity of the section. 



The zonal layer and the more pallid external part of the supraradiary layer, in sections 

 stained for nerve fibres, are the equivalents of this lamina. 



Li/er of Small Pyramidal Cells. 



This is somi'tiiiK's spoken of as the "second layer," but the fuller title is less misleading. 

 Its depth varies in different situations, but is approximately equal to that of the plexiform 

 layer ; the lower border, however, is by no means easy to define, and therefore systematic 

 measurements of the lamina are impracticable. It consists of small elements (average diameter 

 8 10 p) <>f which most are truly pyramidal in form, while some are polymorphous; and 

 though their number is less in some parts than in others, they always have the appearance 

 of being closely-packed, in comparison with the cells of the underlying stratum. 



