Johnston, The Radix Mesencephahca Trigetnini. 641 



One clinical case has come to my notice in the literature wliicli 

 furnishes almost as clear results as could be expected from the second 

 form of operation. This is the case of facial atrophy reported by 

 Mendel (1888). The patient had suffered, twenty-five years before 

 her death, from interstitial neuritis of the left trigeminus. Micro- 

 scopic examination of the trigeminus showed the end products of 

 the neuritis in the root and all the rami, but the maxillary division 

 was very much more seriously affected than any other part of the 

 nerve. In some sections of the maxillary nerve there appeared only 

 small islands of normal nerve fibers among the thick connective tissue 

 septa. The cells of the trigeminal ganglion appeared entirely normal. 

 In the brain the only abnormal changes found were the reduction in 

 the size of the mesencephalic bundle of the trigeminus and reduction 

 in the number of the cells in the substantia ferruginea on the left 

 side as compared with the right. The facial nerve showed no change 

 either centrally or peripherally. The motor nucleus of the tri- 

 geminus was normal. The vesicular cells in the mesencephalon from 

 which part of the mesencephalic bundle arises appeared normal. 

 Mendel interpreted his results as evidence that the mesencephalic 

 bundle had specific trophic functions. The simplest interpretation 

 seems to me to be that the destruction of nerve fibers in the peripheral 

 rami had resulted in retrograde degeneration of part of the fibers of 

 the mesencephalic bundle and atrophy of their cells of origin. The 

 Gasserian ganglion appeared normal, the motor nucleus appeared 

 normal. Either there had been no degeneration in either of those 

 or the atrophy of certain cells had been so complete in the course of 

 twenty-five years that there were no results apparent to Mendel. 

 The Gasserian ganglion, however, had not offered a block to the 

 degeneration of fibers of the mesencephalic bundle passing through 

 it, and the atrophy of cells in the comparatively small locus coeruleus 

 could be detected by counting. The division of the nerve which was 

 much the most deeply affected is ivholly sensory. The obvious con- 

 clusion is that the mesencephalic bundle is sensory in function and 

 this harmonizes with all tire considerations urged in the present 

 paper. 



Although I began the study of this bundle four and a half years 



