MESENCEPHALIC ROOT 191 



(M.R.V.) has assumed a more ventral position than was shown 

 in the more proximal section (fig. 19). The nmnerous degener- 

 ated descending mesencephalic root fibers in it, making up, to 

 venture a guess, one-fifth or less of the total number of fibers, 

 rendered the line of division sharply marked between the motor 

 and sensory roots. Throughout the entire course of these roots 

 there is absolutely no migration of descending mesencephalic root 

 fibers from the motor root to the sensory root. Serial sections 

 from experiments 67 and 68 show identically the same relation- 

 ships between trigeminal motor and sensory roots and that the 

 degenerated descending mesencephalic root fibers are confined 

 solely to the motor root. In series no. 65, where the trigeminal 

 motor nucleus was also partly destroyed in the lesion of the 

 mesencephalic root, it is apparent in figure 28, which is a more 

 or less longitudinal section through the trigeminal roots and the 

 semilunar ganglion, that both trigeminal motor fibers and de- 

 scending mesencephalic root fibers are confined solely to the 

 motor root, and that there is absolutely no intermingling of 

 motor fibers with the sensory fibers, even though there is no 

 connective-tissue sheath separating them. 



Figure 21 shows the position of the trigemmal motor root 

 {M.R. V.) at about the center of the semilunar ganglion. Within 

 the ganglion it is enclosed in a connective-tissue sheath {C.T.). 

 There are fully as many degenerated descending mesencephalic 

 root fibers in the motor root of this section as there were in figure 

 20. I followed the trigeminal motor root section by section, not 

 only in this series, but also in series 67 and 68, and found no 

 descending mesencephalic root fibers leaving the motor root to 

 go to the ganglion. Also figure 28, which happens to be a longi- 

 tudinal section through the trigeminal motor root and the semi- 

 lunar ganglion, demonstrates that the motor root passes straight 

 through the ganglion without giving off any descending mesen- 

 cephalic root fibers or any trigeminal motor fibers to the gan- 

 ghon. It is perfectly clear that the descending mesencephalic root 

 fibers do not end in the semilunar ganglion as May and Horsley 

 supposed, but continue straight through it in the motor root to 

 •enter the nervus masticatorius. 



