286 RESEARCHES ON CORTICAL LOCALISATION AND 



has required little modification, numerous classifications of the 

 various layers of which it is composed have appeared. 



The various subdivisions which have been made by the several 

 authors, owing to the different methods of preparation which have 

 been employed, to the different aspects from which the subject 

 has been studied, and to the different regions of the cortex cerebri 

 which have been examined, have resulted in the employment 

 of different numerals to designate the same or similar layers ; 

 and thereby much confusion has resulted. This will be avoided 

 during the following description by the employment of such 

 terms as clearly indicate the cell layers which are under 

 reference. 



Whilst from the aspect of cell form, few if any of the published 

 descriptions equal in elaboration, and in probable accuracy, the 

 account given by Cajal in the numerous papers he has produced 

 as the result of a systematic employment of various modifications 

 of the method of Golgi, his classification is at present of histo- 

 logical rather than of physiological interest. 



Another and more recent classification, that of Brodmann (1906), 

 is more immediately useful, and, in consequence of the elaborate 

 and prolonged investigations of the author on the subject of 

 cortical localisation, deserves reference here. Brodmann divides 

 the cortex cerebri into the following layers : 



(1) A zonal layer, without cells (the equivalent of the tangential 

 layer of Krause).. 



(2) A layer composed of the " molecular " and " small pyra- 

 midal " layers of other writers. 



(3) A layer of medium and large pyramidal cells. 



(4) An internal granular or stellate layer. 



(5) A layer of ganglionic or deep pyramidal cells. 



(6) A layer of deep spindle-shaped or polymorphous cells. 



For the purposes, however, of this article, which deals with 

 the subject from the functional rather than the structural aspect, 

 the description has been adopted which was published by the 

 present writer in 1900, and which is based on the mode of develop- 

 ment of the several laminae of the cortex cerebri. This classifica- 

 tion, which has been adopted, amongst others, by Mott and by 

 Watson, is as follows : 



(1) The superficial layer of nerve fibres or " molecular " layer 

 (outer fibre lamina). (Average prefrontal depth, -30054 mm.) 



