Telencephalon — Non-olfactory Portions 111 



from the dorsal aspect to the ventral in the rat. This general 

 statement is probably correct for other mammals also, 

 including man. 



The neocortex shows a very definite lamination in its 

 cell-structure, though the laminae are not all so precisely 

 delimited as to bring about complete agreement among the 

 authorities who have studied and enumerated them. Prob- 

 ably the most generally followed scheme is that of Brodmann, 

 who distinguishes six main layers, numbered from the surface 

 inwards as follows: 



I. Lamina zonalis (Plexiform layer) 



II. Lamina granularis interna. (Layer of small pyramidal 



cells) 



III. Lamina pyramidalis. (Layer of medium and large 



pyramidal cells) 



IV. Lamina granularis interna. (Granular layer) 



y. Lamina ganglionaris. (Inner layer of large py- 



ramidal cells) 

 VL Lamina multiformis. (Layer of spindle-shaped 



cells) 



These laminae are to be found throughout the mammalia, 

 but in the rat, as in other rodents, layer II. is practically 

 indistinguishable from layer III., so that only five layers 

 are to be recognized (PI. XXVIL). All the layers superficial 

 to the fifth {i.e., the lamina ganglionaris) probably have 

 receptive and intracortical associative functions, the granular 

 cells giving rise to shorter and the pyramidal cells to longer 

 (inter-regional) association fibres. The two deep layers (V. 

 and VL), on the other hand, contain the efferent neurons of 

 the cortex and send out projection and commissural fibres, 

 though also containing some short-fibred intra-regional 

 correlation neurons. The outer layers have been shown by 

 Bolton to be the only ones in which there are visible changes 

 corresponding with mental defects in man. 



