ON THE FUNCTIONS OF THE CEREBRUM 317 



plicated motor phenomena, which depend on these, and which 

 serve as the sole objective indications of the performance of 

 psychic processes. 



The neopallium is thus the highest sensori-motor ganglion of 

 the mammalia. 



The archipallium is built on a basis which consists primarily 

 of but two cell laminae, which are homologous with the middle 

 (granule) and inner (polymorphous) cell laminae of the neopallium 

 (Turner, Watson). The neopallium is characterised by the ad- 

 ditional development of an outer (pyramidal) cell lamina, which 

 serves as the physical basis of " psychic " in contradistinction to 

 " instinctive " processes. This cell lamina is barely present in 

 the neopallium of the lowest mammalia, and increases in depth 

 with the ascent of the mammalian scale (Brodmann, Watson). 

 It is earliest and also least developed in the projection areas, and 

 is later developed and more highly evolved in the regions con- 

 cerned with associational functions. The human brain is char- 

 acterised by the evolution of a pref rental region of notable size, 

 and of great complexity of histological structure (Flechsig, Bolton, 

 Turner, Watson). The outer cell lamina of this region varies 

 measurably in depth in normal individuals, and in its degrees of 

 evolution and retrogression varies in depth according to the mental 

 capacity of the subjects of mental sub-evolution and dissolution. 



In the earlier evolution of the neopallium, certain projection 

 zones of simple structure exist, together with a rudimentary 

 " motor " area, the function of which is to fuse the products of 

 the projection areas and turn them into motor equivalents. The 

 remainder of the cortex is embryonic in structure (Watson), and 

 is probably latent as regards functional activity. 



During the ascent of the mammalian scale, the projection and 

 motor areas increase in complexity of structure (Brodmann, Elliott 

 Smith, Mott, &c.), and advance in functional activity. Until, 

 however, the carnivora are reached (Campbell), there is no indi- 

 cation of the development of histologically differentiate associa- 

 tional zones around or near the centres of projection. It is probable 

 that, in agreement with the relatively embryonic structure of the 

 rest of the cortex, the functional activity of this is largely latent. 



By|the primates are reached, well-developed and histologically 

 differentiable zones of association exist in the neighbourhood of 

 the projection areas, and similarly developed cortex exists in front 



