GROWTH OF THE FETAL CENTRAL NERVOUS SYSTEM 413 
17. V LH: Volume of the left hemisphere, meninges re- 
moved. 
18. V BH: Volume of both hemispheres: computed by adding 
V RH (16) and V LH (17). 
19. V EB: Volume of the entire brain or encephalon computed 
by adding 13, 14, 15, 16, and 17. This method was found to be | 
more accurate in dealing with the soft brains than to take the 
actual volumes of all the parts, because of the possible loss of 
brain tissue in handling. 
20. VCNS: Volume of the central nervous system; found 
by adding the volume of the spinal cord (12) to the entire brain 
or encephalon volume (19). 
The ponderal determinations corresponding to the volumetric 
measurements were taken and are included in table 41. 
Methods of treating data 
While the accuracy of data of the kind here presented depends 
upon the nature of measures employed and the care with which 
these measures are determined, their significance can only be 
ascertained by the use of a variety of methods of graphic and 
numerical analysis. A number of these methods have been used 
in the present study. They may be arranged in order of pro- 
cedure in five main groups, namely: 1) Construction of field 
graphs with points of central tendency and establishment of pre- 
liminary curves by inspection. 2) Reduction of these prelimi- 
nary curves, as established by inspection, to empirical fomulae 
based on total body length, and construction of primary data 
tables. 3) Calculation of values at 5-cm. intervals of body 
length, calculation of absolute and percentage increments for 
each 5-cm. interval of body length, calculation of newborn ratios 
for each 5-cm. interval of body length, and expression of these 
values in the graphic form. 4) Conversion of the various values 
as determined by empirical formulae from functions of the body 
length to functions of the age in fetal months by interpolation on 
the basis of Mall’s (712) tables of crown-heel length in fetal life. 
Determination of the monthly percentage and absolute increment 
on the basis of these conversions; graphic expression of these 
