ILLUSTRATIONS 



355 



fibers of the ventral median fascicles (1) are turning laterally to enter tr. tecto-bulbaris cru- 

 ciatus in the position of the broken lines under the gray of the interpeduncular nucleus. The 

 thick fibers of tr. tegmcnto-bulbaris shown in figure 60 are here reduced in number, and the 

 thin fibers of tr. tegmento-interpeduncularis are more numerous. These terminals and those of 

 tr. mamillo-interpeduncularis enter into the dense axonic interpeduncular neuropil. 



Pig 62. This detail is from the lower part of the interpedimcular nucleus rostrally of the 



V nerve roots, not far from the plane of figure 91. There is impregnation of a typical large 

 neuron of the trigeminal tegmentum and a smaller element at the border of the interpeduncular 

 nucleus. In the interpeduncular neuropil the visible fibers are nearly all derived from the 

 overlying tegmentum, with perhaps some terminals of tr. mamillo-interpeduncularis. At this 

 level the ventral fascicles (4), (5), and (6) have united to form a compact f. longitudinalis 

 medialis, and the dorsal fascicles spread out laterally into the isthmic neuropil and bulbar 

 tegmentum (compare the horizontal sections, figs. 29-32). 



Fig. 63. — Detail of floor-plate structure immediately caudad of the V nerve roots. Though 

 the interpeduncular nucleus is not considered to extend as far spinalward as this level, the 

 lateral and dorsal interpeduncular axonic neuropil is still rather dense (compare figs. 79, 81). 

 The fibers impregnated here are derived chiefly from the overlying tegmentum, and some of 

 them descend as far as the VII roots accompanying the dorsal and ventral tr. interpedunculo- 

 bulbaris, which is not impregnated in this specimen. Two typical ependymal elements of the 

 bulbar tegmentum are drawn. 



Fig. 64. — This is a similar sketch of the ventral median raphe at the level of the VII nerve 

 roots. A remnant of the tegmento-interpeduncular neuropil persists, and this extends no 

 farther spinalward, though other preparations show that axons from the interpeduncular 

 nucleus reach at least as far as the IX nerve roots. The ependyma here is more compact and 

 mossy than at the level of the trigeminus. 



Figures 65 and 66.— Two transverse sections through the interpeduncular region at the 

 level of transition between the isthmic and the trigeminal tegmentum of the adult. X 50. 

 Each figure is a composite of two adjacent sections, so that four consecutive sections are repre- 

 sented in the two drawings. 



Sections taken farther forward from this well-impregnated series have been shown ('42, 

 figs. 45-47). Between the levels of the III and IV nuclei, tr. tegmento-interpeduncularis is 



