450 HALBERT L. DUNN 
The percentage increment of the midbrain volume, when cal- 
culated for 5-em. intervals of crown-heel length (fig. 26, curve IX), 
is about 45 per cent for the 10-to-15-cm. interval. It rises 
slightly at the 20-to-25-cm. interval and descends to 30 per cent 
for the 50-to-55-cm. interval. 
The percentage increment of the midbrain volume as calculated 
for fetal months (fig. 28, curve IIT) is approximately 81 per cent 
5 
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% 
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Fig. 18 Field graph and curve (connecting the average points of each 5-cm. 
crown-heel interval) of the per cent which the midbrain volume forms of the 
encephalon volume. Abscissa: total body length in em. Ordinate: mid-brain 
volume in per cent of the encephalon volume. Individual cases indicated by 
solid dots. (Data from table 40.) 
in the fourth month and descends to about 25 per cent in the last 
fetal month. ' 
The slow growth of the midbrain is reflected in the per cent 
which this brain part forms of the entire brain volume (figure 18 
and table 40). Beginning at 2.9 per cent at three months, it 
steadily declines to but 0.7 per cent of the entire brain volume 
at birth. 
