2 4 6 



THE GROWTH OF THE BRAIN. 



measure the thickness of the layers in question, and 

 some differences between his results and those of 

 Vulpius probably depend on the fact that owing to 

 condensation, the number of fibres in a limited area does 

 not always run parallel with the absolute thickness of 

 the layer formed by them. 



The medullation is greater in brains of individuals 

 between 38-45 years than in that of a youth of eighteen; 

 so that somewhere in this interval further growth occurs, 

 and from Vulpius we see that it is continued up to at 

 least the thirty-third year. In stained sections in which 

 the layers appear grey, yellow-grey with dark lines, 

 or yellow, according to the abundance of fibres, he 

 found the following proportion of the cortex coloured 

 as indicated in Table 55. 



TABLE 55. SHOWING THE PROPORTIONAL AREA OF THE 

 CORTEX, HAVING THE COLOURS YELLOW, YELLOW-GREY, 

 AND GREY AFTER TREATMENT WITH WOLTER'S STAIN. 

 THE GREYER THE CORTEX THE MORE ABUNDANT THE 

 MEDULLATED FIBRES. (Kaes.) 



This shows the medullated fibres giving the grey tint to 

 be slightly more abundant in the left than in the right 

 hemisphere of the youth of eighteen years, but most 

 abundant in the man of thirty-eight years. The cortex 

 covering the insula was found to be least well developed 



