GROWTH OF THE CORPUS CALLOSUM 49 



1. From birth to fourteen days the callosal area increases 

 relatively slowly. To brain weight = 1 gram; brain area, 

 102 mm.2 



2. Between fourteen days and seventy-five days the callosal 

 area increases relatively very rapidly. To brain weight = 1.74 

 grams; brain area, 145 mm.- 



3. From the seventy-fifth to 378th day the increase is a little 

 more rapid than in the second phase. 



These are approximately the same relations as shown in chart 

 1, B, but presented in a different form. The explanation of the 

 relations is that which was given earlier. 



e. Comparison of the growth ratio between the callosal area, the 



total brain area, and the cortical area {in sagittal section) 



on brain weight 



For this study we utilized the corrected values of the cortical 

 area in sagittal sections from table 1 of Sugita ('18), deriving 

 the values for our series of brain weights from Sugita's data, 

 and these are given in column H, table 4. The data on the 

 brain weights copied from column B, table 2, are given in column 

 C, table 4. If the initial values of the three areas are taken 

 respectively as unity, we obtain ratios for the succeeding values 

 as given in columns E, G, I, table 4. 



These data are presented in chart 4, on the brain weight. 

 From this we see that the ratio of the callosal area increases 

 regularly but slowly up to a brain weight of about 1 gram — 

 equivalent to about twelve days — after which the increase is 

 more rapid. A study of the chart shows that in the case of 

 both the entire brain and the cortex the increase in the ratio is 

 more rapid than in the case of the callosum during the first 

 twenty to twenty-five days (= brain weight of 1.20 grams), 

 while after that it is slower. 



Generally speaking, the growth rates of these areas just 

 mentioned show a rapid increase during the first twelve days, 

 and after this period the growth rate becomes slower and the 

 three curves take a somewhat parallel course. 



