GROWTH OF THE CEREBRAL CORTEX 509 



2. The greatest width (W.B), the greatest length (L.G) and 

 the height (Ht.) of the cerebrum at birth are respectively 8.6, 

 7.1 and 5.4 mm. The same measurements at full maturity are 

 respectively 15.4, 16.7 and 10.0 mm. (table 3). The ratio of 

 each measurement in the mature brain to its initial value at 

 birth is, therefore, respectively 1.78, 2.34 and 1.86. Using the 

 product of these three diameters as a measure the ratio of volume 

 of the mature cerebrum to the volume at birth is 7.74. 



3. The increase in the ratio of the weight of a cerebrum accord- 

 ing to age is quite equal to the increase in the ratio of total 

 weight of the brain, which includes the cerebellum, the stem 

 and the olfactory bulbs, besides the cerebrum. Thus the de- 

 velopmental stage of the cerebrum (in weight) corresponds to the 

 developmental stage of the entire brain (in weight). 



4. As the cerebrum increases its volume with age, it does not 

 enlarge proportionally in all dimensions. In general, the length 

 increases most rapidly while the width and height increase more 

 slowly. However, in the period between the tenth and the 

 twentieth day after birth (brain weight 0.95 to 1.2 grams), 

 the cerebrum is enlarging in volume quite uniformly in all its 

 dimensions. 



5. In the newborn cerebrum the width is greater than the 

 length (width-length index, ^127). After birth, the increase in 

 the longitudinal diameter surpasses that of the transverse diame- 

 ter and finally at full maturity the cerebrum has a somewhat 

 elongated form (width-length index 95). 



6. Sex differences in the size and shape of the cerebrum are not 

 significant, when brains of like weight are compared. 



7. A rough estimation indicates that the specific gravity of 

 the brain increases after brain has attained 1.2 grams in weight. 

 This is due probably to myelination. 



