170 THE BRAIN OF THE TIGER SALAMANDER 



cells of this nucleus. These two systems of fibers are mingled, and 

 analysis is impossible except in electively impregnated material. We 

 have few such specimens of either Amblystoma or Necturus, but 

 those we have show that in the ventral commissure immediately spinal- 

 ward of the decussation of the f. retroflexus some of the visceral- 

 gustatory fibers turn forward in company with those of the ventral 

 secondary visceral tract, and both groups of fibers arborize in the 

 ventrolateral neuropil of the peduncle. Some of these fibers probably 

 pass through this neuropil without synapse to reach the hypothala- 

 mus, as in fishes, in company with pedunculo-mamillary fibers and 

 mingled with those of the mamillo-peduncular, mamillo-tegmental, 

 and mamillo-interpeduncular tracts. At their decussation the tertiary 

 visceral fibers spread in the alba of the isthmic tegmentum before and 

 after crossing, and some of them probably reach the interpeduncular 

 neuropil, though this needs confirmation. All these systems and 

 others (including, perhaps, mamillo-cerebellar fibers) are mingled, 

 and none of the tracts are closely fasciculated. 



In some fishes these tracts are separately fasciculated, and the am- 

 phibian arrangement, so far as revealed in our material, conforms 

 with the teleostean pattern. The tertiary visceral-gustatory tract is 

 very large in some of these fishes ('05, pp. 420, 436, figs. 20, 23, 37, 

 38), passing from the secondary nucleus directly to the hypothala- 

 mus. This direct connection has been described by Larsell ('23, 

 p. 109) in the frog; and in both Amblystoma and Triturus he saw 

 some indications of it. In the frog these direct fibers do not take the 

 deep course, as described above for Amblystoma, but are superficial, 

 accompanying mamillo-cerebellar fibers. I find evidence of this super- 

 ficial connection in Amblystoma also, but in the absence of elective 

 impregnations no accurate description can be given. These fibers in 

 some of our preparations are seen as a well-fasciculated tract. In the 

 Cajal sections, from which figures 25-36 were drawn, it is not so 

 clearly shown as in some other specimens, but its location can be 

 identified. These fibers assemble at the lateral surface rostrally of 

 tr.v.a. (fig. 34), in company with those of tr.t.b.p., as drawn in that 

 figure. Ten sections farther ventrally, they are drawn, but not la- 

 beled, in figure 33 superficially of tr.t.h.r. In some Golgi preparations, 

 fibers in this position connect with the hypothalamus, and this is the 

 course taken by the tertiary visceral tract in the frog (Larsell, '23, 

 figs. 2, 4). This is the position also of the tr. mamillo-cerebellaris, 



