Ingbekt, Ventral Roots of Spinal Nerz'cs. 231 



BiRGE (1882) counted the number of fibers in all the dor- 

 sal and ventral roots of three frogs [Rana cscuknta) having 

 body-weights of 23, 60 and 63 grams respectively. The ratios 

 individually were : 



Frog-Weight Ratio 



23 grms. 1:1.07 



60 grms. 1:1.14 



63 grms. 1:1.24 



Average for all three frogs = 1:1.15, or rounding the num- 

 ber for the decimal = 1:1.2. 



Stannius_(i849) states that in fish, as a rule, the ventral 

 roots are larger than the dorsal. There are, however, a num- 

 ber of exceptions to this relation. In estimating the value of 

 this statement in the present instance, it must be remembered 

 that the ratios already given are between the numbers of fibers, 

 and that in a comparison like this, the number of fibers and 

 area of roots do not necessarily v^ary together. In the case of 

 fish, the number of fibers in the roots has not }'et been de- 

 termined in any instance. 



Tabulating these results, we have the following: 



Ventral Dorsal 



Frog I : 1.2 



White Rat i 



Man 1 



In this series increasing rank 

 companied by a relative increase of the number of fibers in the 

 dorsal roots. 



5. Relation Betiucen the Small and the Large Fibers in the 

 Ventral and Dorsal Roots. — According to the author's estimate, 

 the ventral roots contain 39.64% of nerve fibers the diameter 

 of which is less than 7.5 // and the dorsal roots 60%. The com- 

 parison may therefore be made as follows : 



Diameter of fibers. Ventral roots. Dorsal roots. Ratio. 



7.5 i-i and greater 122,953 272,451 1:2.2 



Less than 7.5 /< So, 747 381,176 i:4-7 



It thus appears that, compared with the ventral roots, the 

 dorsal roots are more than twice as rich in fibers, the diameter 

 of which is 7.5 /i or more and nearly five times as rich in fibers 

 less than 7. 5 // in diameter. 



2-3 



3-2 

 n the zoological scale is ac- 



