MESENCEPHALIC ROOT 181 



nucleus or thereabouts. From figure 8 it is also apparent that a 

 considerable number of these fibers have continued past the 

 trigeminal motor nucleus and are traveling side by side with the 

 descending mesencephalic root fibers in the region of the locus 

 coeruleus (Loc.C). This is more evident in figure 10, which 

 mcludes the mesencephalic roots and locus coeruleus cells from 

 the same section as figure 8, but more highly magnified to permit 

 of the accurate drawing of every particle of degenerated myelin. 

 The figure at the left is from the lesion side and a number of 

 degenerated ascending sensory fibers will be seen in the mesen- 

 cephalic root, while the right mesencephalic root (non-lesion' 

 side) does not contain any more degenerated fibers than an area 

 a little median. In this figure the difference in number of 

 degenerated fibers on the right and left sides represents the 

 actual number of ascending sensory fibers in the mesencephalic 

 root near the level of the exit of the trochlear nerve. The globu- 

 lar unipolar cells of the locus coeruleus {Loc.C.) are in marked con- 

 trast to the large multipolar cells of the trigeminal motor nucleus 

 (fig. 6, M.V.). 



There appears to be a gradual reduction in the number of 

 degenerated fibers in tracing the left mesencephalic root cephalad 

 through the inferior colliculus up to the level of the trochlear 

 nucleus. In figures 12 and especially 13, which shows the 

 mesencephalic root of figure 12 more highly magnified, it is 

 perfectly evident that there are more coarse degenerated fibers 

 in the left mesencephalic root (lesion side) than in the right. 

 The difference in number will represent the number of ascending 

 sensory fibers in the mesencephalic root at a level, slightly 

 caudal, to the trochlear nucleus. It should be noted for this 

 section that there are more fine particles of degenerated myelin 

 scattered throughout the entire section than were present in 

 more caudal sections. So far as could be determined, there were 

 no more degenerated ascending mesencephalic root fibers on the 

 operated side, cephalad of the trochlear nucleus, than on the 

 opposite side, indicating that the ascending sensory fibers of the 

 mesencephalic root did not extend cephalad of the level of this 

 nucleus. 



