GROWTH OF THE FETAL CENTRAL NERVOUS SYSTEM 483 
The curve of absolute temporal diameter (fig. 9) is also a 
straight line when based on crown-heel length. Starting at about 
1 cm. at the 5 cm. (C Hy), it increases steadily to about 72 cm. 
at 50 cm. (C H). Its empirical formula is: 
Temporal diameter (cm.) = 0.1388 C H body length (cm.) 
+0.3 
When studied in relation to time (fig. 32, curve IT), this diam- 
eter is found to be 1 cm. at the beginning of the third fetal 
0 5 10 15 c0 05 30 35 40 £45 50 55cm 
Fig. 9 Field graph and curve of the growth-of the cerebral hemispheres in 
fetal life as shown by the temporal diameter. Abscissa: total body length 
in em. Ordinate: temporal diameter in em. Individual cases indicated by 
solid dots. Curve drawn to the formula: Y = 0.138X +0.3. (Datafrom tables 
15 and 16.) 
month and to rise at first fairly rapidly and then more slowly to 
7.2 em. at birth. 
The rate of growth of the temporal diameter (fig. 25, curve IT) 
decreases steadily from 70 per cent for the 5-to-10-cm. interval 
to about 10 per cent for the 50-to-55-cm. interval. : ; 
The percentage increment of the temporal diameter, when cal- 
culated for fetal months (fig. 27, curve II), is approximately 
70 per cent in the fourth fetal month and falls to about 35 per 
