GROWTH OF THE CEREBRAL CORTEX 



507 



brain, attaining at maturity over thirty-four times its initial 

 weight. This will be one of the reasons why the relative weight 

 increase of the total brain is greater than the relative volume in- 

 crease of the cerebrum only. 



2. The specific gravity of the brain substance is probably in- 

 creasing as the age advances, especially after the brain has at- 



O 02 B af 



Brain weight in qrams. 



Chart 2 Showing on brain weight by smoothed graphs, the ratios of the width 

 W.B., the length L.G. and the height Ht, as compared with the cube root of the 

 brain weight y^ C- 



tained 1.2 grams in weight, for as already determined by Watson 

 ('03) the myelination of the brain begins in the albino rat at the 

 age of fourteen to twenty days and this process, which increases 

 the specific gravity of the brain, continues most energetically 

 during and after the fourth week, when the brain attains 1.2 to 

 1.3 grams in weight. 



3. Finally it is at about this period, when the brain has reached 

 1.2 grams in weight, that the more rapid growth in the length 

 appears and the change in the proportions between the lengths of 



