ARCHITECTURAL CHANGES DUE TO GROWTH. 24! 



maturity is followed with care, changes of great interest 

 are to be discerned, and these changes are apparently 

 open to much individual variation. Their importance 

 is enhanced by the fact that on the one hand the cortex 

 is the most complicated group of the central cells by 

 which cross references between incoming and outgoing 

 impulses are established, and on the other by the fact 

 that the changes in question have been shown to occur 

 during the period of formal education, and may there- 

 fore be in some measure influenced by it. The accom- 

 panying diagram represents on one side in a schematic 

 manner the distribution of the cells in the occipital 

 region of the human cortex, and on the other the 

 arrangement of the fibres. The facts which are to be 

 presented bear on the relative development of these 

 layers of fibres as indicated by their increasing medul- 

 lation (Fig 47). 



The change with age in the number of tangential 

 medullated fibres or those running parallel with the 

 cortical surface has been studied by Vulpius. 1 For the 

 purpose of this investigation, the cortex was divided 

 into three layers, an outer (A,B, C and outer half of D\ 

 middle (D, inner half), and inner (E to H inclusive), repre- 

 sented respectively by the layers I, II ; III, and IV, 

 to VIII in Fig. 47. The proportional number of the 

 fibres was determined by counting them in a small area. 

 Six localities in a large number of brains ranging in 

 age between the thirty-second week of fcetal life and 

 seventy-nine years were studied. The results are par- 

 tially summarised in the two figures which follow, in 

 which is recorded the proportional development of 

 tangential fibres under the conditions named. The 

 figures show that between the age of sixteen months 

 and thirty-three years the number of fibres in all the 



1 Vulpius, Archiv. f. Psychiat. u. Nervenkrank. Bd. xxiii. 1892. 



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