296 RESEARCHES ON CORTICAL LOCALISATION AND 



such as the insectivora, only of an insignificant absolute depth 

 subserves the higher associations, the capacity for which is shown by 

 the educability of the animal. It has therefore to do with all those 

 activities which it is obvious that the animal has acquired (or per- 

 fected) by individual experience, and with all the possible modifica- 

 tions of behaviour which may arise in relation to some novel situation, 

 hence with what is usually described as indicating intelligent as apart 

 from instinctive acts, the former being not merely accompanied but 

 controlled by consciousness (Lloyd Morgan)." 



The middle cell lamina (3, granule) is developed after the fifth, 

 polymorphic, or inner cell lamina, and before the second, pyramidal, 

 or outer cell lamina. In the prefrontal region of a foetus of six 

 months it has just become differentiated, by commencing specialisa- 

 tion of its constituent cells, from the superjacent second or outer 

 cell lamina, and it is already one-half of the normal adult depth. 

 In a child at birth it has become three-fourths of the normal adult 

 depth. 



In the visuo -sensory area the optic radiations end in the midst 

 of a hypertrophied and duplicated third or granule layer. The 

 duplication is due to the interposition in the midst of the hyper- 

 trophied third or granule layer of a well-marked fibre band, the 

 line of Gennari, which fibre band, as has already been stated, is 

 a hypertrophy of the outer of the two horizontal interradiary fibre 

 plexuses of the adult cortex, namely, the " outer line of Baillarger." 

 In old-standing or congenital optic atrophy, the outer (and addi- 

 tional) of the granule layers is decreased in thickness by more than 

 10 per cent., and the line of Gennari is decreased in thickness by 

 nearly 50 per cent. 



As has been pointed out by Watson, a hypertrophied third, 

 granule, or middle cell lamina appears to be characteristic of the 

 projection areas of the cerebrum. In the case of the visuo- 

 sensory area (visual projection sphere), the third or granule layer 

 first becomes definitely duplicated in the order primates, though 

 slight indications of duplication occur in the higher carnivores. 



The third, granule, or middle cell lamina, therefore, primarily 

 subserves the reception or immediate transformation of afferent im- 

 pressions, whether these arrive directly from the lower sensory neurones 

 or indirectly through other regions of the cerebrum. 



The fifth, polymorphic, or inner cell lamina is the first cell lamina 

 of the cortex cerebri to be differentiated during the process of 



