MESENCEPHALIC ROOT 189 



a certainty, from sections, which of the trigeminal nerves con- 

 tained motor fibers and which contained none. In this series the 

 left trigeminal roots became curved outward somewhat during the 

 process of fixation so that the roots and semilunar ganglion appear 

 in almost perfect longitudinal section. 



From series no. 64 it is apparent that the degenerated de- 

 scending mesencephalic root fibers within the pons follow the 

 descriptions of this root given by Johnston, and May and 

 Horsley. After leaving the inferior colliculus a little lateral to 

 the aquaeductus cerebri and median to the brachium con- 

 junctivum, its fibers intermingle with the cells of the locus 

 coeruleus and undoubtedly receive fibers from these cells. In 

 fact, the cells of- the locus coeruleus appear to be nothing more 

 than a caudal continuation of the mesencephalic root cells of the 

 midbrain. In the pons region the mesencephalic root (figs. 14, 

 15, and 17, Mes.V.) continues caudad through the locus coeruleus 

 directly median to the brachium conjunctivum {Br.C.) and dorsal 

 to the trigeminal motor nucleus {M.V.). At the caudal ex- 

 tremity of the trigeminal motor nucleus the degenerated de- 

 scending mesencephalic root fibers (fig. 14, Mes.V.) bend lateral 

 and ventral, to assume a cephalic course between the trigeminal 

 sensory (substantia gelatinosa) and motor nuclei (figs. 15 and 17, 

 Mes.V.). This cephalic arm of descending mesencephalic root 

 fibers continues cephalad in the trigeminal motor root for some 

 distance cephalad of the trigeminal motor nucleus. In figure 18, 

 which is about .twenty sections cephalad of the trigeminal motor 

 nucleus, the trigeminal motor root with its numerous inter- 

 mingled degenerated descending mesencephalic root fibers {Mes. 

 V.) will be seen passing to the median side of the trigeminal 

 sensory root (S.R.V.). Fifty-two sections cephalad, in figure 19, 

 both motor and sensory roots (M.R.V. and S.R.V.) will be found 

 outside the pons, and all of the degenerated descending mesen- 

 cephalic root fibers are confined absolutely to the trigeminal 

 motor root {M.R.V.). The truth of this statement can be easily 

 confirmed by turning to figure 11, where the area of degenerated 

 ascending fibers from the semilunar ganglion conforms exactly to 

 the light area in figure 19 designated as the sensory root, and the 



