GROWTH OF THE FETAL CENTRAL NERVOUS SYSTEM 417 
from Mall’s tables of the relation of crown-heel length to age in 
prenatal life (Keibel and Mall, Human Embryology, vol. 1, p. 
199). The results obtained by this procedure are not to be 
regarded as final, for the exact relation between body length and 
age in fetal life is still open to question. They are included, how- 
ever, because they give, in a rough way at least, some concept 
of the relation of the growth of the central nervous system to 
time in the prenatal period and because they aid in the inter- 
pretation of its percentage increment. Since Mall’s table stops 
at 270 days, it has been extended by graphic exterpolation to 
ten full lunar months (280 days) and the length at this age (51.5 
em.) was considered as the norm for the new-born in this type 
of calculation. The monthly percentage increments of the prin- 
cipal volumetric determinations were calculated secondarily from 
the values obtained in this manner. They are shown in table 42. 
5. Determination of the relative weights of the various parts of the 
central nervous system in terms of per cents of the encephalon is an 
obvious procedure which needs no particular description. The 
results obtained are shown in table 40. 
SUMMARY OF OBSERVATIONS 
Growth of the central nervous system as a whole 
The curve of the absolute volume of the central nervous system 
(fig. 2), when based upon crown-heel or total body length, is con- 
cave like all other curves of volume growth of the fetal organs. 
It may be expressed by the empirical formula: 
Central nervous system volume (cc.) = [0.114 (C H length 
em.) ]*-34 + 2.0 
The absolute volume of the central nervous system is about 
7 ec. at 10 to 15 em. (CH). This increases steadily to 36 ce. 
at 25 em. (C H), and is then deflected upward sharply to reach 
3a/ cc. at 50 cm. (CH). 
When calculated according to age in fetal months, the absolute 
volume of the central nervous system (fig. 34, curve I) is found to 
be 2 cc. at the beginning of the third month, rising to 36 ce. at the 
beginning of the sixth month, and to about 340 ce. at birth. 
