COKTEX OF FOEEBEAIN AND MEDULLA OF HEMISPHERES. 233 



deeper in the third layer, nearer to the fourth, and not so high up as is shown 

 for the frontal lohe in Fig. 151. 



The medullated fibers in the superradial net-work probably come, foe 

 the most part, from fibers radiating into the cortex from without. It is very 

 questionable whether the cells with the short, branched neuraxons have 

 medullated processes. The line of Gennari is formed entirely by the col- 

 laterals of the neuraxons from the pyramidal cells. The interradial net- 

 work consists likewise of the collaterals from the neuraxons of the pyramidal 

 cells, and perhaps also of the arborization formed by the cells with the short, 

 branched neuraxons. 



It must not be expected that these lines, etc., will be found uniformly 

 well developed. Disregarding the fact that they are variously well defined, 

 according to the zone of the cortex, developmental investigations also show 

 that very considerable differences may exist accordiag to the age. Probably 

 it will be proved, when we at last recognize a fixed type for all the parts of 

 the cortex and all ages of life, that definite relations exist between the in- 

 telligence of the individual and the number of fibers in his cortex. 



The discoveries of Kaes along these lines are promising much. He was 

 able to show by means of numerous accurate measurements that the cerebral 

 cortex increases in richness of fibers for a long time, even to the fortieth year 

 and longer. Tracts come particularly under consideration that pass along 

 within the basal portion of the medullary rays in a direction parallel with 

 the surface, fibrse arcuatte intracorticales, and then tracts of fibers which, 

 lying within the superradial net-work, follow closely on the layer of tan- 

 gential fibers. Medullation occurs here very late in some portions of the 

 cortex; so that a very great part of the cortex below the layer of tangential 

 fibers is gradually traversed by delicate fibers. According to Kaes, still 

 larger medullated fibers are added to. these, which, in the course of years, 

 are seen to extend very gradually toward the surface of the cortex from the 

 layers lying next to the medulla. It is probably the fibers of this plexus, 

 some very large, which Bechterew has described and by which he saw formed 

 a distinct line lying just beneath the layer of tangential fibers: Bechterew's 

 line. Fig. 153, which I owe to the kindness of Dr. Kaes, illustrates well the 

 difl'erent types of cortex and at different times of life. 



As far as can be seen at present, these are all neiu association-pathways, 

 or at least pathways which, only called into use late in life, become medul- 

 lated at a late period. It is possible, also, that we are concerned with col- 

 laterals, which, with the greater demand consequent upon increased asso- 

 ciations, now attain their complete development: the formation of the 

 medullary sheath. It is known that in other tissues also an acceleration of 

 growth may occur, owing to an increased demand made iipon the elements. 

 Thus, the similar process in the cerebral cortex should present nothing that 



