ON THE FUNCTIONS OF THE CEREBRUM 293 



in lamination takes place, layer 36, the line of Gennari, suddenly 

 ceasing, and layers 3a and 3c, the two layers of granules, running 

 into one and becoming layer 3 of the visuo-psychic region, which 

 is thus of the ordinary five-layered type. 



Congenital or long-standing blindness causes no modification of 

 the lamination of the visuo-psychic region, which fact proves that 

 this region possesses no " visuo-sensory " functions. 



The cortex of this region reaches maturity later than the visuo- 

 sensory, but earlier than the prefrontal. The second, pyramidal, 

 or outer cell layer in infants of one and three months is respec- 

 tively nearly two-thirds and more than three-quarters of the 

 normal adult depth. This layer reaches to practically the same 

 adult depth as in the prefrontal region. In cases of mental disease 

 this layer does not vary in depth according to the degree of 

 dementia existing in the patients, though a small and practically 

 constant decrease in depth, which may be due either to sub- 

 development or to retrogression, is evident in such cases. 



The Prefrontal Region. The cortex of this region is late in 

 reaching maturity. As hps been stated, the pyramidal or outer 

 cell lamina ?s the last layer of the cortex to develop. It is visible 

 owing to the undifferentiated condition of its constituent neuro- 

 blasts in a fo3tus of six months, and is at this time only one- 

 quarter of the normal adult depth. In infants at birth and at 

 the age of six weeks it is still less than two-thirds of the normal 

 adult depth. 



It is the only cell layer of the cortex cerebri which varies 

 measurably in depth in " normal " brains. 



In cases of mental disease it is under-developed to different 

 degrees, not only in idiots and imbeciles, in the severer grades of 

 which its depth is only two-thirds of the adult normal, but also, 

 and here to a lesser extent, in chronic and recurrent lunatics 

 without dementia. The degree of its retrogression in demented 

 patients varies directly, and to an equally marked degree as its 

 subdevelopment in the case of amentia, with the amount of 

 dementia existing in the respective cases. 



Of these three " regions of the cortex, therefore, the visuo- 

 sensory area first reaches maturity. Though highly specialised, 

 the cortex of this area is, however, not well developed, as the 

 outer cell lamina or pyramidal layer remains at but five-ninths of 



