GROWTH OF THE FETAL CENTRAL NERVOUS SYSTEM 
One of the most interesting facts concerning the prenatal 
growth of the pons and medulla is the per cent of the entire brain 
volume which they form during fetal life (fig. 15 and table 40). 
In the middle of the fourth fetal month the pons and medulla 
make up 5.5 per cent of the entire brain volume, at 5 months they 
TABLE 23 
Volume of the pons and medulla 
Formula: Pons and medulla volume (ec.) = .01 [(.2 crown-heel length 
(em.) )?-§7 + 20] 
(112 cases) 
CROW N-HEEL LENGTH 
OBSERVED PONS 
AND MEDULLA VOLUME 
Range Mean Bae 
cm. cm. ce. 
Oto 5 
5 to 10 
10 to 15 1256 O25 
15 to 20 16295 ORG 
20 to 25 DOEo 1.0 
25 to 30 tbe) eal War! 
30 to 35 Sth | pal | 
35 to 40 SY/ UME Bee 
40 to 45 42.3 3.9 
45 to 50 48.0} 5.5 
50 to 55 8222 | 6:3 
Mini- 
mum 
cc. 
PWNEe OOOO 
or SI OD O 
Hm e bo 
On 
CALCULATED pea 
PONS AND | op cERVED AND 
| Mean “VOLUME ye ee | 
ce. cc. aa 
ORS 0.3 0 
oe te +0.1 
0.8 0.8 0 
ni teh +0.2 
< we +0.2 
2.4 2.3 0.1 
ae: He +0.1 
ae Be +0.1 
i ce 40.2 
TABLE 24 
NUMBER 
OF CASES 
Calculated pons and medulla volume at 5-cm. intervals of crown-heel length 
CROW N-HEEL LENGTH 
PONS AND 
MEDULLA VOLUME 
INCREMENT IN EACH 
ce. 
5-CM,. INTERVAL 
per cenit 
00.0 
56.5 
04.1 
49.0 
43.5 
38.3 
34.2 
30.8 
27.4 
RATIO TO NEW-BORN 
per cent 
5.3 
8.0 
12.5 
19.3 
28.7 
41.2 
57.0 
76.4 
100.0 
128.0 
443 
