GROWTH OF THE FETAL CENTRAL NERVOUS SYSTEM 487 
Cerebellum volume (ce.) + [0.01 (0.07 Vermis cerebelli 
height (em.) = 2.45)*]? 
These indicate that the cerebellum volume is growing at relatively 
the same rate as are its vertical and horizontal diameters. The 
growth of the cerebellum must be controlled, therefore, by factors 
which act alike upon the entire cerebellum. 
The formulae of the fronto-occipital length and the temporal 
diameter when cubed bear no relation to the cerebrum volume 
which may be expressed by a simple constant, and the same 
holds true of the spinal cord length when cubed. It is obvious, 
therefore, that in all other brain parts except the cerebellum 
there must be more than one factor influencing growth which act 
differently on the volumetric and linear growth. 
The per cent of the brain parts and the spinal cord of the encepha- 
lon. The per cent which the various brain parts and the spinal 
cord form of the encephalon at each fetal month can be observed 
by a glance at table 40 and at figures 7, 11, 15, 18, 22, and 38. 
Table 40 tabulates the per cent which a respective volume of a 
brain part or of the spinal cord forms of the encephalon. Figures 
7, 11, 15, 18, and 22 demonstrate graphically the per cent whichthe 
pons and medulla, midbrain, and the spinal cord, respectively, 
form of the encephalon volume. Figure 38 represents a series of 
composite midsagittal sections which are based upon average 
measurements and which represent therefore a typical fetal brain 
for the 5-em. C. H. interval indicated. For purpose of compari- 
son, a magnification of each individual figure was used. To 
obtain this magnification, the ratio of the respective fronto- 
occipital diameters to the fronto-occipital diameter of the new- 
born was used. The detailed results of both figures and the table 
have been presented in the body of this paper. Taken in toto, 
the evidence shows conclusively: first, the high percentages which 
the pons and medulla, midbrain, and the spinal cord volumes 
form of the encephalon volume from the second to the fifth fetal 
month; second, the increased percentages which the cerebellum 
volume forms of the encephalon volume in the last three fetal 
months, and, third, the predominating percentages which the 
