GROWTH OF THE FETAL CENTRAL NERVOUS SYSTEM 459 
the growth of the central nervous system to the growth of other 
parts of the body it has been considered as a unit. It is however 
a complex of four distinct subtypes of growth, all of which are 
dominated by the growth of the bulky cerebral hemispheres.? 
Jo} 
4 
55cm 
Fig. 22 Field graph and curve (connecting the average points of each 5-cm. 
crown-heel interval) of the per cent which the spinal cord volume forms of the 
encephalon volume. Abscissa: total body length in em. Ordinate: spinal 
cord in per cent of the encephalon volume. Individual cases indicated by solid 
dots. (Data from table 40.) 
2In order to compare these four types of growth, ten methods were used: 1) the 
various absolute length curves (fig. 29) were calculated against crown-heel body 
length (em.) and reduced to a percentage basis; 2) the absolute volume curves 
likewise (fig. 30) were taken to crown-heel length and reduced to a per cent basis; 
3) the absolute length curves (fig. 33) were calculated for age in fetal months and 
reduced to a common per cent; 4) the absolute volume curves also (fig. 36) were 
taken to age in fetal months and reduced to a percentage basis; 5) percentage 
increments of linear curves (fig. 25) were calculated for 5-em. C H intervals; 
