MESENCEPHALIC ROOT 173 



of the trigeminus were cut. They call attention to the fact that 

 these observations do not support Johnston's view that the ax- 

 ones of the mesencephalic root enter the trigeminal sensory root. 

 Furthermore, they found that no chromatolysis took place in 

 the locus coeruleus cells, indicating that these cells do not belong 

 to the mesencephalic root. 



In order to determine the ultimate distribution of the cen- 

 trifugal (descending) axones of the mesencephalic root. May and 

 Horsley applied the Marchi method of staining the degenerated 

 medullary sheaths, after first destroying this root in the region 

 'of the inferior colliculus. They made serial sections of the 

 brains and gasserian ganglions and also sectioned identified 

 portions of the main trunks of the trigeminal nerves peripheral 

 to the ganglion, from which they were able to trace the mesen- 

 cephalic root fibers around the trigeminal motor nucleus and out 

 the motor root of the trigeminal nerve to the gasserian ganglion. 

 Since no degenerated fibers were found in the nerve trunks 

 peripheral to the ganglion (ophthalmic, maxillary, and mandib- 

 ular nerves), they thought that these fibers ended, in the gas- 

 serian ganglion. The authors observed that this mode of termi- 

 nation of the mesencephalic root fibers would seem to be incom- 

 patible with their previous statement that some chromatolysis 

 occurs after the mandibular nerve had been cut, but call at- 

 tention to a point made by Warrington that chromatolytic 

 changes resulting from a lesion of the anterior and posterior 

 roots of a spinal nerve affect not only the cells in direct asso- 

 ciation with the fibers divided, but also other cells forming a 

 part of the same nerv^e center. So that they appear to discount 

 somewhat their first results obtained from a study of chroma- 

 tolysis. 



In a clinical case where the gasserian ganglion had been de- 

 stroyed and the patient Hved several weeks after the operation^ 

 May and Horsley found from an examination of Marchi sections 

 of the brain stem that there were many fine and a few coarse 

 degenerated centripetal (ascending) fibers in the mesencephaUc 

 root. In some experiments on cats and monkeys where the 

 trigeminal nerve fibers were severed centrally and peripherally 



