A488 HALBERT L. DUNN 
volume of the cerebral hemispheres form of the encephalon 
volume at all times, rising to its maximum per cent (94.2 per 
cent) in the sixth fetal month. 
SUMMARY 
I. The growth of the central nervous system in the fetal period 
is similar in general character to the growth of the other viscera 
and of the major parts of the body in this period. 
II. An analysis of data on the volume and dimensions of the 
central nervous system in the fetal period shows four distinct 
subtypes or varieties of growth. These are: 
1. The cerebral subtype, which is characterized by, a) a steady 
and relatively slow increase in volume from the second to the 
beginning of the sixth fetal month and a constant and more rapid 
increase from this time to birth, and, b) by a steady and constant 
growth in linear dimensions from the second fetal month to 
birth. 
2. The brain stem and cord subtype, which shows a much more 
rapid growth from the second to the end of the fifth fetal month 
than it does in the last five months of fetal life. 
3. The cerebellum subtype, which proceeds very slowly from 
the second to the end of the fifth fetal month and then increases 
tremendously from the sixth month to birth. 
4. The compound subtype, which represents the combined 
effect of two or three or all of the above varieties, predominated 
by the cerebral subtype. 
Ii. The factors which control the various subtypes of growth 
in the central nervous system may influence the volumetric and 
linear determinations of a respective brain part in two ways: 
1) the factors may act differently upon the volumetric and linear 
values as they do in the case of the cerebral growth, brain stem, 
and cord growth, and in compound growth, or, ,2) they may 
act in the same manner as they do in the case of the cerebellum 
subtype of growth. 
IV. An estimation of the percentages which the cerebrum, 
cerebellum, and the brain stem form of the encephalon at the 
various periods of fetal life offers a means of comparison of the 
