88 BRAINS OF RATS AND MEN 



and spreading them out in thin sheets (p. iG) so that 

 each cell can effect synaptic junctions with incoming 

 fibers at both ends. 



The non-olfactory cortex (neopallium) of mam- 

 mals everywhere presents a quite different picture 

 from the archipallium. Its neurons are typically 

 pyramids with a big dendrite directed outward and 

 the axon directed inward into the white matter. 

 These cells are arranged in layers (four to ten) which 

 differ in form and arrangement of cells and fibers in 

 the various cortical fields. Gray (1924) has pubhshed 

 a more detailed description of this arrangement in 

 the cortex of the opossum than we have for any other 

 lower mammal. Figure 14 shows the arrangement of 

 cortical cells in the area parietalis, the somesthetic- 

 motor field of the opossum. Here the six typical 

 cortical layers as defined by Brodmann are obscurely 

 evident. In higher brains, these laminae are more 

 sharply defined and the differences between the vari- 

 ous cortical areas are greater. In the human brain, up- 

 ward of fifty such cortical areas can be distinguished. 

 Illustrations of the more complicated cortical patterns 

 of man are given in all of the larger manuals of neu- 

 rology, and these details need not be elaborated here. 



The greater thickness of the neopaUial cortex and 

 a different type of intercellular connections necessi- 

 tate a cellular pattern different from that of the 

 archipallium. The neurons are of very diverse forms 

 and those of each of the different layers make 



