188 WILLIAM F. ALLEN 



both trigeminal roots attached on each side, together with the 

 semihmar ganghon and all of the branches of the trigeminal 

 nerve on the left (lesion) side. The series from experiment 

 no. 64 demonstrated that the lesion, in addition to severing all 

 of the mesencephalic root fibers taking origin from the mesen- 

 cephalon, included at least one-half of the fibers originating from 

 the locus coeruleus, with absolutely no damage to the trigeminal 

 motor nucleus (figs. 14, 15, 17, and 18). In experiment no. 65 

 all of the mesencephalic root fibers from the midbrain and most 

 of the locus coeruleus fibers were severed by this lesion, which also 

 extended into the trigeminal motor nucleus, causing a degenera- 

 tion of at least one-half of the motor root fibers. The lesion in 

 experiment no. 67 was almost identical to experiment 64, except 

 that it was a little more cephalad and severed fewer locus coeru- 

 leus fibers; while the lesion in experiment no. 68 was a little 

 deeper than no. 64, severing more locus coeruleus fibers and 

 coming very close to the trigeminal motor nucleus, which it may 

 have injured, from the fact that a few degenerated fibers were 

 found in the main mandibular trunk and none were present in 

 series 64 and 67. 



A careful study was made of all the series, which checked up 

 identically in so far as the distribution of the mesencephalic root 

 fibers was concerned. Most of the description and nearly all of 

 the figures were taken from series no. 64 for the reason that we 

 are absolutely certain in this experiment that all of the descend- 

 ing mesencephalic root fibers were severed without injury to the 

 trigeminal motor nucleus or root. It will be seen from figure 18 

 that all of the descending mesencephalic root fibers {Mes.V.) 

 taking origin from cells in the midbrain were severed by this 

 lesion (Les.). From figures 14, 15, and 17 it is apparent that 

 the lesion {Les.) passed through the locus coeruleus (LocC), 

 severing at least half of its fibers. From these figures, which 

 also pass through different levels of the trigeminal motor nucleus 

 (M.V.), it is perfectly evident that the lesion (Les.) does not 

 come near enough to the nucleus to injure it. Series no. 65, in 

 addition to being useful for tracing the distribution of the de- 

 scending mesencephalic root fibers, enables one to determine for 



