PLATE 1 



EXPLANATION OF FIGURES 



1 Transverse section through the brain stem of a small child at the level 

 of the caudal end of the inferior coUiculus (corpora quadrigemina), treated 

 after a modified Marchi method for demonstrating degenerated medullary 

 sheaths. Observe the size of the glioma, which was still larger more caudally,. 

 having involved the trigeminal roots on both sides in their course through the 

 brachium pontis. The marked degeneration of the mesencephalic and troclear 

 roots shown in this figure and in figure 2 cannot be attributed solely to a de- 

 generation process, progressing centrally, as might be surmised from the fact 

 that the region of the cells of origin of these two roots had not been invaded by 

 the tumor. X 1.2. 



2 Portion of the left mesencephalic root from the same section as figure 1. 

 but more highly magnified to show the practically complete degeneration of the 

 fibers of the mesencephalic root. X 4.8. 



3 Dissection of the left trigeminal nerve of a guinea-pig. The sensory 

 components are drawn in outline and the motor are cross-barred. There is 

 some doubt as to the identification of the chorda tympani, but a nerve so^desig- 

 nated was found leaving the lingual nerve close to its union with the inferior 

 alveolar and to pass toward the tympanic bulla. X 1.6. 



4 Photograph of the ventral surface of a guinea-pig's skull to show the large 

 foramen in the alisphenoid, designated as the semilunar ganglion foramen, 

 through which the trigeminal roots c^n be destroyed without the necessity of 

 drilling through the stuU. X 4/5. 



5 to 13 are from a transverse series of 20/* sections through a brain stem of a 

 guinea-pig (experiment no. 58), in which the 'left trigeminal roots had been 

 completely severed by an electric cautery immediately behind the semilunar 

 ganglion, and the material to be sectioned was treated after a modified Marchi 

 method for demonstrating medullary sheath degeneration. 



5 Left half of a transverse section through the brain stem of a guinea pig 

 (ex. 58) at the level of the caudal end of the trigeminal motor nucleus. Observe 

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

 in its sensory nucleus (substantia gelatinosa). Between the trigeminal sensory 

 and motor nuclei will be seen numerous degenerated ascending mesencephalic 

 root fibers, which took origin from cells in the semilunar ganglion and from 

 which many fibers and fine collaterals are sent to the trigeminal motor nucleus 

 and to a group of smaller cells situated directly above and median to the sensory 

 nucleus. X 8. 



6 Portion of the left mesencephalic root /rom the same section as figure 5 

 more highly magnified so that every particle of degenerated myelin of any size 

 could be accurately sketched. X 48. 



204 



