MIDBRAIN AND THALAMUS OF NECTURUS 249 



which closes in the anterior diverticulum of the recessus later- 

 alis ('14, pp. 2, 3 and fig. 22) and lies farther laterally and mor- 

 phologically (though not anatomically) farther caudad. Ven- 

 trally of this nucleus and laterally of the dorsal part of the emi- 

 nentia subcerebellaris tegmenti are a few scattered neurons in 

 the stratum album, two of which are illustrated in figure 18 

 of my former paper ('14). These apparently do not belong to 

 the secondary visceral nucleus, though their lateral dendrites 

 arborize within the secondary visceral tract near its termination 

 and probably receive nervous impulses from it. 



In larval Amblystoma, where the recessus posterior of the 

 tectum mesencephali is wide and deep (see '14 a, p. 353 and 

 fig. 2, r.p.m.,) this nucleus lies in the posterior wall of this evagina- 

 tion in front of the isthmus; it belongs, therefore, in the mid- 

 brain rather than in the medulla oblongata. 



In Necturus the secondary \asceral tract or visceral lem- 

 niscus is wholly unmyelinated and, as in larval Amblystoma 

 ('14 a, figs. 5, 6, 52, 54), it ascends from the medulla oblongata 

 ventrally of the tractus spino-cerebellaris and dorsally and 

 laterally of the acoustico-lateral lemniscus and tractus bulbo- 

 tectalis. It does not appear in Weigert sections, though its 

 locus can be readily identified by comparison with the Cajal 

 and Golgi sections (fig. 14, tr.v.a.). The fibers of this tract 

 in our Golgi preparations are very slender and unusually vari- 

 cose. At the level of the isthmus they lie at the extreme ventro- 

 lateral surface of the brain in the angle between the auricular 

 lobe and the midbrain. Here the tract divides into two parts, 

 some of the fibers continuing forward ventro-laterally of the 

 eminentia subcerebellaris tegmenti and others turning abruptly 

 dorsally to reach their nucleus. The latter fibers cross the 

 tractus bulbo-tectalis superficially and then turn medialward 

 to arborize in the secondary visceral nucleus (figs. 50 to 54, 66, 

 tr.v.a. and nuc.vis.s.). 



We have no complete impregnations of the neurons of the 

 secondary visceral nucleus or of the tertiary visceral tract aris- 

 ing from it. Dendrites and axons of some of these cells are 

 seen in figure 50, nuc.vis.s. In Cajal and Golgi sections a slen- 



