482 HALBERT L. DUNN 
The volumetric formulae of the right hemisphere volume, left 
hemisphere volume, and both hemisphere volume (table 43) are 
all expressed by the simple formula: 
Y = (aX) 
in which Y is the value to be determined in cc.; X, the crown- 
heel length in cm., and a and b are constants for the respective 
volumes. | 
Brain stem and spinal cord growth. The growth of the brain 
stem and spinal cord, as shown by curves of absolute linear di- 
mensions and absolute volumes, represents a second definite type 
of growth in the central nervous system. It is characterized by 
a relatively rapid absolute and relative increase previous to the © 
sixth fetal month and a slow increase during the last four months 
of intra-uterine life. 
The linear determinations showing this type of growth are the 
frontospinal length, the spinal cord length, and the brain-cord 
length. When plotted against crown-heel length in centimeters 
and reduced to percentages of new-born values (fig. 29, curves 
VII, VIII, and IX) these three curves approximate one another 
and ascend more rapidly prior to the sixth fetal month than they 
do in the last four months. They are distinctly separated from 
the cerebral type of growth and, when calculated in fetal months 
and reduced to a per cent of the new-born (fig. 33, curves VII, 
VIII, and IX, respectively), they show even more clearly the 
almost identical path which they all follow. When calculated to 
time, they likewise show a rapid increase to the fifth fetal month 
and a comparatively slow one thereafter. The rates of growth of 
the brain stem and the spinal cord as shown by these three linear 
determinations can be observed equally well when taken for 
5 cm. intervals: (fig. 25, curves VII, VIII, and IX, respectively), 
or when calculated for age in fetal months (fig. 27, curves VII, V, 
and VI, respectively). The brain stem and spinal cord grow at 
a slower rate both relatively and absolutely than do all other 
brain parts during the last four months of fetal life. 
The classification indicated by comparison of the absolute 
linear curves is substantiated by a glance at their respective 
