222 Journal of Comparative Neurology and Psychology. 



obtained by Stilling and that obtained by the author, has the 

 same explanation as the difference in the total number of fibers 

 — Stilling did not include the fibers, the diameter of which 

 was less than 7. 5 11, and at the same time, for some reason not 

 yet apparent, his areas are large. 



In Tables VIII-XXXVIII and Figures 8-38, are given the 

 number of fibers per sq. mm. in each fascicle expressed in 

 thousands. A study of these shows that great variations may 

 occur in the neighboring roots, and even in fascicles of the same 

 root. The small number per sq. mm. in the roots forming the 

 brachial and lumbo-sacral plexuses is due to the large fibers in 

 these roots, there being relatively few small fibers in them. 

 The large number per sq. mm. in the thoracic region is due to 

 the very great number of small fibers, many of which, no doubt, 

 pass to the white rami communicantes. The large number per 

 sq. mm. for the root C. Ill, correlated with the small size of 

 this root, indicates a small diameter for the fibers in this root. 



In order to show better the relation between the number 

 of fibers in the roots and the area of the cross-sections of roots, 

 I have constructed, on the basis of the data in Table IV, Fig. 

 3 (see p. 213). These curves has been drawn in the same 

 manner as the corresponding chart in the author's earlier paper 

 (Ingbert, June, 1903, p. 72). 



2. Discussion of Figure j. — In this figure the relative 

 areas of the ventral roots are contrasted with the relative abund- 

 ance of the fibers in them. 



For each series the largest value is taken as 100%, and the 

 other values are calculated on this as a standard. As the root 

 with the largest area (C. V.) is also the root with the largest 

 number of fibers, the two maxima coincide. It is sufficient in 

 this place to call attention to the fact that in the intumescentiae 

 the number of fibers and the area of the roots change in the 

 same manner, so that the two curves are parallel, and that in 

 the thoracic region the number of fibers remains relatively 

 large while the area of the roots is much diminished, thus show- 

 ing that in these roots the diameter of the fibers is on the average 

 much decreased. 



