PLATE 2 



EXPLANATION OF FIGURES 



7 Portion of the right mesencephalic root from the same section as figure 5, 

 but from the opposite or non-lesion side, A comparison with figure 6 shows a 

 great reduction in the number of degenerated fibers. No more are present 

 than would appear in any other field of this section not affected by this lesion 

 or would occur in a similar section of a normal brain. X 48. 



8 Left half of a transverse section fron the same series as figure 5 (ex. 58), 

 but at the level of the cephalic end of the trigeminal motor nucleus. Observe 

 the complete degeneration of the trigeminal sensory root and the fine collaterals 

 in the trigeminal sensory nucleus (substantia gelatinosa). Degenerated as- 

 cending mesencephalic root fibers appear in transverse section in the locus 

 ca?ruleus and intermingled with the trigeminal motor root fibers midway between 

 the trigeminal sensory and motor nuclei. A few degenerated mesencephalic root 

 fibers and collaterals will be seen in the trigeminal motor nucleus. X 8. 



9 Similar transverse section to figure S, but nineteen sections cephalad. This 

 section is at a higher level than the trigeminal motor nucleus and shows a number 

 of degenerated ascending mesencephalic root fibers in the locus coeruleus directly 

 median to the brachium conjunctivum. The trigeminal motor root is about to 

 join the sensory root from the median side. It contains a few degenerated 

 fibers, but too few to be of any significance X 8. 



10. Mesencephalic roots and locus coeruleus cells from the same section as 

 figure 9 sufficiently magnified so thai every particle of degenerated myelin 

 could be accurately sketched, Note that no more degeneration is shown in the 

 right mesencephalic root (non-lesion side) than occurs outside this tract, while 

 considerable degeneration is present on the left (lesion) side and many of the 

 degenerated fibers are of large size. X 48. 



11 Left half of a transverse section through the same guinea-pig's brain as 

 figures 1 to 10 (ex. 58), but near the level of the caudal end of the inferior col- 

 liculus (corpora quadrigemina) at the exit of the trochlear nerves. Observe the 

 mesencephalic root in transverse section directly median to the brachium con- 

 junctivum. There are fewer degenerated fibers in the mesencephalic root than 

 in the section from which figures 9 and 10 were drawn, which is twenty-eight 

 sections further caudad. As was noted for figure 9, there are a few degenerated 

 fibers in the trigeminal motor root, which at this level is ventral as well as median 

 to the sensory root. X 8. 



12 Similar view of a transverse section from the same series as figure 11, 

 but through the inferior colliculus a little caudal to the trochlear nuclei. Note 

 a few coarse degenerated fibers and a number of fine particles of myelin in the 

 mesencephalic root. X 8. 



206 



