SUMMARY OF CORTICAL EVOLUTION 259 



and these must be built into the main lines of through 

 traffic. The reflex centers of the brain stem are thus 

 developed at the nodal points of conduction where the 

 pathways of the great reflex systems intersect. But 

 the cortex is set apart from the intersection of trunk 

 lines of reflex conduction in a separate field. The 

 through traffic of the basal centers may go on without 

 interference by the shifting, sorting, and redirection 

 of nervous activities which take place in the cortex, 

 or it may be held up while the results of cortical ac- 

 tivity are assembled and discharged into the trains of 

 reflex and instinctive behavior. 



5. This implies that intrinsic cortical activities in 

 their definitive form are also dissociated in time from 

 the immediate reactions through which they are 

 activated (Minot, 1902). There is, however, no evi- 

 dence that this is true of the simpler forms of cerebral 

 cortex. The temporal dissociation of cortical from 

 subcortical functions appears clearly only in those 

 more complex kinds of cortex where much associa- 

 tional tissue is interpolated between the more primi- 

 tive cortical projection centers. 



6. The diversity involved in associations of cor- 

 tical type is such that cortex never develops within 

 or associated with a single center which is physiologi- 

 cally dominated by some one functional system (ol- 

 factory, optic, or any other), though it may develop 

 in relation with several such centers conjointly. In 

 fact, the simplest well-differentiated cortex known 



