MEDULLA OBLONGATA OF AMBLYSTOMA 365 



slender prefacial portion of the fasciculus is composed chiefly of the 

 ascending branches of root fibers from the VII, IX and probably 

 also the X nerves. In horizontal longitudinal sections of both 

 larval and adult brains it can easily be followed forward nearly 

 to the extreme rostral end of the auricular lobe. At the level of 

 the superficial origin of the V nerve (fig. 9) it lies dorsally of the 

 V root fibers and internally of the VIII fibers, a relation which is 

 preserved to the rostral end of the auricular lobe. 



In larval Amblystoma the fasciculus solitarius has no appa- 

 rent connection with the V nerve, and if any V root fibers enter it 

 their number is certainly small. In the adult a few medullated 

 fibers are seen in horizontal sections to leave the sensory V root 

 at its superficial origin and to pass inward to the fasciculus soli- 

 tarius, where they turn caudad within or in close proximity to 

 this fasciculus. In adult Cryptobranchus alleghaniensis these 

 fibers from the V root are more numerous than in Amblystoma. 



The rostral terminus of the prefacial fasciculus solitarius is an 

 ill defined deep-seated area of neuropil internally of the terminus 

 of the V and VIII root fibers in the auricular lobe. In figure 6 

 it lies in an undesignated area immediately dorsally of r.V, 

 In the adult this neuropil lies close to the stratum griseum ros- 

 trally of the motor V nucleus and laterally of similar large neu- 

 rones in the caudal part of the eminentia subcerebellaris tegmenti 

 which is the direct forward continuation of the motor V nucleus. 

 The latter neurones correspond in position to the locus coeru- 

 leus of mammals and may be homologous with this nucleus. All 

 relations of the prefacial fasciculus solitarius are much clearer in 

 the adult brain than in the larva, but as I have no satisfactory 

 Golgi impregnations of this region I am not able to give further 

 details. This terminal neuropil of the fasciculus solitarius lies 

 a short distance caudad and laterad of a larger and more clearly 

 defined area of neuropil in the isthmus which receives the ascend- 

 ing secondary visceral tract (see p. 373 and figs. 5, 6, 52, tr.v.a.) 

 and is apparently the amphibian equivalent of the teleostean 

 ''Rindenknoten" (Mayser '81), or superior secondary gustatory 

 nucleus (Herrick '05), but there seems to be no direct connection 

 between the fasciculus solitarius and this secondary visceral 

 nucleus. 



