ORIGIN OF THE CEREBRAL HEMISPHERES 453 



which numerous functionally distinct fields are well separated 

 in space and are at the same time in free communication through 

 systems of association fibers of unHmited complexity, which 

 find ample room in the subcortical white matter. There is no 

 assignable limit to which structural specialization of this sort 

 can extend. The nutritive requirements of the tissue are readily 

 satisfied by its superficial position in close apposition with the 

 rich blood vascular supply of the pia mater and with the cerebro- 

 spinal fluid of the meningeal spaces. 



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