SUMMARY OF CORTICAL EVOLUTION 265 



facts is that every cortical association pattern when 

 once activated leaves the synaptic thresholds (or 

 whatever may be the apparatus of facilitation of path 

 by use) in a different structural arrangement or "set" 

 which makes the reactivation of these neurons in this 

 particular pattern easier than it was before. The 

 thing which is preserved is static, a changed structur- 

 al arrangement of parts. 



II. The features so far considered appear to be 

 characteristic of some, at least, of the infrahuman 

 types of cerebral cortex, some more, some less. The 

 human cortex presents these features and some very 

 significant additional structural patterns. The dif- 

 ferences between the larger anthropoids and man 

 are relatively unimportant except those related to 

 the cerebral cortex and the behavior. 



The wide gap between the highest living anthro- 

 poid and man has not been bridged. The enormous 

 increase in the size of the human cortex is chiefly in 

 the associational fields. Here, then, is to be sought 

 the structural organization upon which depend hu- 

 man culture and the progress of civilization. The fea- 

 ture which most distinguishes these associational 

 fields from the rest of the cortex is their greater 

 wealth of strictly intracortical associational connec- 

 tions. This is obvious anatomically. With this are 

 probably joined physiologically: (i) a greater im- 

 pressionability or susceptibility to those structural 

 changes (engrams) to which reference has already 



