GENERAL PHYSIOLOGY OF THE CEREBRUM. 



177 



animals the greater mental development is associated with a greater 

 complexity and richness in the connections of the neurons. As 

 shown in Figs. 79 and 80, the number of processes, particularly 

 the dendritic processes, is much greater in the cortical cells 

 of the higher animals; or, to put this fact in another way, the 

 number of cells in the cortex of the higher animals is much less 

 for an area of the same size than in lower animals. The amount 

 of in-between substance or the richness of the network of processes 





> I' 



A > ' 



A <* 



V' S " 



r 





m 





9 





, v 4 * 



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Fig. 80. Sections through corresponding parts of the cortex in: a, Man; &, dog; 

 and c, mole, to show the greater separation of the nerve cells in the higher animals. 

 (Bethe, after Nissl.) 



is increased. This anatomical fact would indicate that the greater 

 mental activity in the higher animals is dependent, in part, upon 

 the richer interconnection of the nerve cells, or, expressed physio- 

 logically, our mental processes are characterized by their more 

 numerous and complex associations. A visual or auditory stim- 

 ulus that, in the frog, for instance, may call forth a comparatively 

 simple motor response, may in man, on account of the numerous 

 associations with the memory records of past experiences, lead to 

 12 



