294 RESEARCHES ON CORTICAL LOCALISATION AND 



the maximum adult depth. The visuo-psychic cortex attains to 

 maturity later, but then becomes of the maximum adult depth. 

 The prefrontal cortex is the last to reach maturity. The outer 

 cell lamina in this region varies in its degree of development 

 according to the mental capacity of the individual and in its degree 

 of retrogression according to the amount of mental decadence 

 which exists. Further, it varies in measurable depth in " normal " 

 individuals. 



All these variations regarding the degree of development occur 

 in the pyramidal or outer cell layer, which is the last lamina to 

 be evolved, and the most important feature of the human adult 

 cortex cerebri. 



The inner cell lamina or polymorphic layer of the cortex, which 

 is the first to be evolved, is, on the other hand, in all the three 

 regions referred to above, of extremely constant average depth. 

 A very slight decrease in the average depth of this layer occurs, 

 in the prefrontal region, in cases of mild cerebral and mental 

 degeneracy (high-grade amentia), and in cases of chronic insanity 

 with moderate dementia. A considerable decrease, on the other 

 hand, exists, also in the prefrontal region, in more marked aments 

 (whether normal foetuses and infants, or idiots and imbeciles) and 

 in gross dements who are unable to carry on the ordinary animal 

 functions, such as attending to their own wants, &c. 



FUNCTIONS OF THE DIFFERENT CELL LAMINA OF 

 THE CORTEX CEREBRI 



As has been stated, the cerebral cortex consists of three primary 

 cell laminae (layers 2, 3, and 5), and of two primary fibre laminae 

 (layers 1 and 4). The evidence above adduced regarding the 

 ontogenetic and phylogenetic development of these laminae enables 

 certain definite conclusions to be drawn with regard to their 

 functional significance. 



The outer cell lamina (2, pyramidal), to which may be added 

 the outer fibre lamina (1), is the prominent feature of the human 

 cortex, and constitutes a " higher level " basis for the carrying 

 on of the cerebral functions. It is the last cell layer of the cortex 

 to be evolved and the first to undergo retrogression. In the 

 visuo-sensory area (projection sphere) the outer cell lamina rapidly 

 attains maturity, but is then only about five-ninths of its depth 



