MEDULLA OBLONGATA OF AMBLYSTOMA 373 



which these fibers originate is very incomplete, but so far as it 

 goes it suggests that they come from the group of neurones which 

 I have designated above (p. 372) as substantia gelatinosa Rolandi, 

 and chiefly in the vagus region. This tractus bulbo-tectaHs would 

 therefore be, in part at least, the trigeminal lemniscus, with proba- 

 bly a certain gustatory or general visceral element also repre- 

 sented. 



The ascending secondary visceral tract (tr.v.a.) is apparently 

 the amphibian equivalent of the teleostean secondary gustatory 

 tract (secondary vagus bundle of Mayser). It terminates in an 

 area of neuropil in the isthmus region which has already been 

 mentioned (p. 365) as the probable representative of the superior 

 secondary gustatory nucleus of teleosts (Herrick '05), or ''Riden- 

 knoten" of Mayser ('81); see figures 5, 6, 52, tr.v.a. Dendrites 

 of neurones which apparently belong in the basal part of the body 

 of the cerebellum enter this neuropil, and this is the same region in 

 which I have seen termini of the tractus mammillo-cerebellaris of 

 Necturus ('14, fig. 19). This neuropil is conspicuously developed 

 in adult Amblystoma and unmedullated strands are directed 

 forward and downward from it toward the hypothalamus at a 

 deeper level than the tractus mammillo-cerebellaris. These may 

 contain the tertiary gustatory tract, as I have found it in fishes 

 ('05). 



In figure 39 the most dorsal dendrite shown on each side arises 

 from a neurone whose cell body lies dorso-laterally of the fascic- 

 ulus solitarius, and in figure 44 two similar neurones are impreg- 

 nated. The dendrites of these neurones arborize chiefly among 

 the fibers of the correlation tract b of Kingsbury and the axones 

 are directed medialward toward the ventral commissure. These 

 neurones would, therefore, seem to be adapted to transmit 

 impulses from the ventral correlation tract of the area acustico- 

 lateralis to the opposite side of the oblongata. Their further 

 connections are unknown. 



The connections of the two longitudinal tracts a and b are like- 

 wise unknown. Fibers are seen to pass between both of them and 

 various fasciculi of root fibers and also the system of arcuate 

 fibers. Kingsbury ('95, p. 175) states that in Necturus arcuate 



