26 BRAINS OF RATS AND MEN 



this factor, as illustrated by the deeply imbedded 

 lamellated and convoluted masses of gray found in 

 the inferior olive and the dentate nucleus of the 

 cerebellum. 



Various attempts have been made to define 

 cerebral cortex in terms of the number of synaptic 

 junctions which intervene between it and the pe- 

 ripheral sensory surfaces from which it receives its 

 afferent fibers. This criterion is seen to be of doubtful 

 value in many cases, as, for instance, in the cortex 

 of the pyriform lobe and anterior hippocampus, 

 where in the opossum I have shown (1924^^) that both 

 of these cortical sheets receive fibers directly from the 

 olfactory bulb separated by only one synapse from 

 the nasal epithelium. 



Kappers (1913, 1914, 1921) calls attention to other 

 functional factors in the problem, especially to the 

 fact that in all reactions where spatial relations of 

 stimuli and responses enter into the process of adjust- 

 ment the nervous pathways and correlation centers 

 must maintain their specific separateness. This is 

 facilitated by spreading the adjusting apparatus out 

 in plane surfaces. The case is much hke that of a 

 telephone exchange. The wires which come into the 

 building compactly in cables are widely spread out 

 over the switchboards to facilitate precise and rapid 

 connection of any incoming call with any one of the 

 outgoing wires. 



These switchboard arrangements are adapted for 



