Hartal, Spenal Nerves of the Rat. 179 
weight of 10.3 and 25.4 grams, after which the increase is 
slower. In this respect the changes in the ventral roots are 
similar to those found in the dorsal roots. 
Comparison of the number of the dorsal root fibers at 
10.3 and 264.3 grams’ indicates nearly the same rate of 
increase as is found for the ventral roots. The following table 
shows this : 
TRABEE lle 
Relative Increase of the Medullated Dorsal and Ventral Root Fibers. 
Weight of VI Cervical IV Thoracic II Lumbar 
Rat Dorsal Ventral Dorsal Ventral Dorsal Ventral 
10.3 I I I I I I 
264.3 2.0 a7 2.9 Pela] 2.9 2.8 
As the table indicates, the total number of the dorsal root 
fibers of the 264.3 gram rat is about twice that of the I0.3 
gram rat in the cervical region, while in the thoracic and 
lumbar regions the fibers are nearly three times as numerous. 
The different ratio shown between the three regions is probably 
due to the fact that the number of dorsal root fibers in the 
cervical region increases more rapidly between birth and 10.3 
grams, than in the case of the two other regions. This special 
relation, however, should be further investigated. 
A comparison between the number of the ventral and 
dorsal root fibers presents an interesting relation. 
TABLE III. 
Comparison Between the Number of the Medullated Ventral and 
Dorsal Root Fibers at Different Ages. 
Weight of Rat. 10.3 25-4 68.0 164.9 264.3 
Root Wentia Dorssam Vin Dies SVin el): Vi» Vie Ds 
VI Cerv. 558 Ig98 1007 2569 1302 3683 1474 4227 1522 4028 
IV Thor. 286 607 434 863 561 1420 613 1522 772 1650 
II Lumb. 333 723 698 9Q11 704 1317 1028 1644 965 2102 
Total Number ~=1177 3328 2139 4343 2567 6420 3115 7393 3259 7780 
Ratios I PCO Ab 2 I Pats i at) | PERU Vee Mpa. 
1The observation on this animal has been made since the previous work 
('02) was published. 
