Ingbekt, Ventral Roots of Spinal Saves. 227 



general when the area of a dorsal root changes, it is due to a 

 change in the number of nerve fibers composing it, while the 

 average diameter of the fibers remains about the same from 

 root to root. This is also expressed by the fact that the num- 

 ber of thousands of fibers per square millimeter (see Ingbert. 

 June, 1903. p. d']) undergoes but slight variation. 



If the corresponding curves for the ventral roots are now 

 examined, some interesting differences between the ventral and 

 dorsal roots at once appear. In the ventral roots (see curves 

 in Figs. 6 and 7) the enlargement of the areas of the cross-sec 

 tions is not due so much to an increase in the number of fibers 

 in the roots as to the increased diameter of the nerve fibers ; 

 ht-nce at the intumescentiae the curve for the areas rises far 

 above the curve for the number of the fibers. In the same 

 way this fact is expressed by the number of thousands of fibers 

 per square millimettr of the cross-section of the different ventral 

 roots of the cord, which ranges from 5 in the intumescentiae to 

 about 12 in the thoracic region (see Table II). 



,\ Relation of the Number of Nerve Fibers in the Ventral 

 and Dorsal Roots. The relation between the number of nerve 

 fibers in the ventral and dorsal roots, as estimated by Stilling 

 and enumerated by the author, is as follows: 



Ventral roots Dorsal roots Ratio 



Stilling (femalej 149,058 262,919 i:i.8 



Author (male) 203,700 653,627 1:3-2 



A large part of this difference in ratio is no doubt due to 

 the fact that Stilling failed to include about 39.64% of the 

 nerve fibers in the ventral roots, and about 60% of those in the 

 dorsal roots, or in other words Stilling's numbers as given 

 above are only about 61 % of the ventral and 40% of the dorsal 

 fibers, which were probably present. Another factor is the 

 relatively large size of the ventral roots in Stilling's case, as 

 already mentioned. 



In order better to compare the number of fibers in the dif- 

 ferent ventral and dorsal roots, the curves of Fig. 5 have been 

 constructed from data recorded in Table VI. The ordinates 

 have been obtained by taking the largest number of each series 



