MESENCEPHALIC ROOT 171 



number of guinea-pigs had been severed, a little behind the 

 inferior colliculus (corpora quadrigemina) , and the degenerated 

 fibers were traced into the motor root and nerves, I became con- 

 vinced that by far the greater number of fibers in the mesenceph- 

 alic root were descending rather than ascending, and that the 

 mesencephalic nucleus or root in the little girl must have been 

 injured by pressure in. the region of the midbrain, if not through 

 direct destruction by the tumor. The details and discussion of 

 the results of the above-mentioned experiments will form the 

 basis for this paper. 



REVIEW OF THE LITERATURE 



Johnston and Edinger have given a very complete review of 

 the literature of the mesencephalic root to 1909 and 1911, re- 

 spectively, so that it is inadvisable to go into detail over the 

 early history of this Work here. It seems that the first investi- 

 gator of this root, namely, Me>Tiert, considered it as sensory, 

 but the majority of the authors, Forel, Koelliker, Van Gehuchten, 

 and Cajal, regarded it as motor. Several of them, however, 

 called attention to the similarity of the balloon-shaped unipolar 

 cells of the mesencephalic root to spinal ganglion cells. From 

 Golgi preparations Cajal noted that many very fine collaterals 

 were given off from the mesencephalic root fibers to form a 

 delicate network about the bodies of the trigeminal motor cells. 

 He suggested that a relatively very weak stimulus could be in- 

 tensified into a very strong one by such a mechanism. According 

 to Cajal, the locus coeruleus cells constitute a separate system, 

 which is not directly connected with the trigeminal nerve. On 

 the other hand, Held claims that the mesencephalic root takes 

 origin from cells in the mesencephalon and from the locus 

 coeruleus. Bregmann states that a lesion of the motor portion 

 of the trigeminal nerve produced a degeneration of the mesen- 

 cephalic root. Wallenberg obtained a descending degeneration of 

 the mesencephalic root as a result of a lesion of the tectum 

 mesencephalic in birds. 



Johnston made a most comprehensive morphological study of 

 the mesencephalic root from Weigert serial section of the brains 



