200 THE BRAIN OF THE TIGER SALAMANDER 



commissure and then descend in the ventral and ventrolateral fas- 

 cicles of the medulla oblongata. Horizontal sections of one of these 

 larvae show slender collaterals of these decussating fibers, which are 

 directed posteroventrally into the interpeduncular neuropil and here 

 have tufted endings in the interpeduncular glomeruli ('396, p. 600 

 and figs. 46 and 59). Figures 67 and 68 of the present work show 

 similar collaterals, as seen in transverse sections from the same lot of 

 larvae. Each compact glomerulus-like tuft contains terminals of sev- 

 eral of these collaterals. Figure 69 shows similar collaterals in an 

 adult brain. In this preparation only a few of these decussating fibers 

 are impregnated, and these can be followed from section to section. 

 Nothing else is stained here, so there is no opportunity for confusion. 

 Figure 60 is from another adult specimen which shows some of these 

 features more clearly, though the impregnation is less selective. This 

 section is from the series illustrated in 1927 and is a few sections ros- 

 trally of figures 39 and 40 of that article. The tufted axonic termi- 

 nals shown there are similar to the one seen in the present figure 60, 

 and they are now known not to be derived from the mamillo-pedun- 

 cular tract as there suggested ('27, p. 280). 



Tertiary visceral-gustatory tract. — These fibers, as elsewhere de- 

 scribed (p. 169), pass from the secondary visceral nucleus in the isth- 

 mus to the area ventrolateralis pedunculi. They lie close to the gray 

 in the posterior lip of the sulcus isthmi and form one component of 

 the complex f. tegmentalis profundus. Some fibers of this fasciculus 

 decussate in the ventral commissure dorsally and spinalward of the 

 decussation of the f. retroflexus, and here in some preparations there 

 is evidence that fibers of the tertiary visceral tract turn spinalward 

 to enter the interpeduncular neuropil. Several other systems of simi- 

 lar fibers are mingled here, and, in the absence of elective impregna- 

 tion of this connection, its presence remains doubtful. Whether or 

 not this direct connection exists, the visceral-gustatory system is re- 

 lated less directly with the interpeduncular nucleus by way of the 

 hypothalamus. The secondary visceral nucleus is connected with the 

 dorsal (mamillary) part of the hypothalamus and from here the large 

 tr. mamillo-interpeduncularis may transmit visceral sensory and 

 gustatory influences to this nucleus. 



Other afferent fibers to the interpeduncular nucleus have been de- 

 scribed in various animals. Gillilan ('41) reports that in bats and ro- 

 dents the basal optic tract sends some fibers directly to this nucleus. 



