ILLUSTRATIONS 343 



passes through the ventral border of the eniinentia thalami. Large numbers of thick fibers pass 

 from the ventral thalamus to the peduncle and isthniic tegmentum {tr.th.teg.r.), both super- 

 ficially and deeper in the alba. Similar fibers (not drawn) arise from the large cells of the 

 peduncle, which comprise a primordium of the mammalian interstitial nucleus of the f. longi- 

 tudinalis niedialis. Many of the thalamic and most of the pedimcular fibers enter ventral 

 tegmental fascicles of group (5) (see p. 281). Tiiis section cuts tegmental fascicles of group (3) 

 at the dorsal convexity of their course as they recurve around the tuberculum posterius. 



Fig. 32. — Section passing just above the interventricular foramen and through the middle 

 of the eminentia thalami. Accompanying fibers of the hippocampal commissure are those of 

 tr. cortico-habenularis medialis for the stria medullaris and tr. cortico-thalamicus niedialis 

 (primordium of the column of the fornix). Thick fibers stream backward from the ventral 

 thalamus in tr. thalamo-tegmentalis rectus, some superficially, some at middle depth, and 

 some at the inner border of the alba, the latter entering dorsal tegmental fascicles of group (8). 

 Similar fibers arise from the larger cells of the peduncle, but to simplify the pictures these have 

 not been drawn in figures 31 and 32. Most of them enter tegmental fascicles of group (5), and 

 some of these continue spinalward in f. longitudinalis medialis. The more ventral large cells of 

 the peduncle (fig. 31) correspond with the interstitial nucleus (Cajal) of f. longitudinalis me- 

 dialis, the more dorsal of these cells (fig. 32) to the nucleus of Darkschewitsch (p. 217 and figs. 

 6, 18). For further details see the analysis of the tegmental fascicles in chapter xx and references 

 there given. 



At the level of figure 32, tegmental fascicles of groups (4), (5), and (10) are cut at the dorsal 

 convexity of their courses through the peduncle, and here they are insinuated among the 

 fibers of the anterior and posterior divisions of tr. tecto-bulbaris cruciatus, descending from 

 the tectum toward their decussations. Farther back in the posterior isthmic neuropil the bulbar 

 and spinal lemniscus systems {Im. and Im.sp.) are turning upward and forward to ascend in 

 the dorsal tegmentum (figs. 33, 34). The wide auricle contains terminals of vestibular and 

 lateral-line root fibers, other bulbar connections, and nucleus cerebelli. 



Fig. 33. — This passes through the floor of the stem-hemisphere fissure, cutting the most 

 dorsal fibers of tr. cortico-habenularis medialis as they enter the stria medullaris and the dorsal 

 border of the eminentia thalami. Fibers of tr. thalamo-frontalis are seen emerging from the 

 ventral border of the dorsal thalamus. Large cells of the nucleus of Darkschewitsch occupy 

 the dorsal border of the peduncle. Laterally of these, tegmental fascicles (7) and (9) are re- 

 curving over the peduncle, and two sections farther dorsally, fascicles of group (8) are cut at 

 the top of their convexity. More posteriorly the section passes through the dorsal border of the 

 central nucleus of the isthmic tegmentum, laterally of which a few fibers of the brachium con- 

 junctivum are impregnated. Some of these are seen to arise from the nucleus cerebelli. Exter- 

 nally of this nucleus is the posterior neuropil of the isthmus containing dendrites from the 

 superior visceral-gustatory nucleus, terminals of the ascending secondary visceral tract {tr.v.a.), 

 and many other components. Behind the auricle the section passes through the ventral part 

 of the lateral recess of the ventricle and spinalward of this through the "dorsal island" of 

 Kingsbury. 



Fig. 34. — Ten sections farther dorsally, all components of the stria medullaris can be identi- 

 fied in the ventral habenular nucleus. The tr. habenulo-thalamicus (tr.hab.ih.) contains fibers 

 passing in both directions between this nucleus and the thalamus and regions posteriorly of it. 

 The bulbar lemniscus (Im.) and the spinalJemniscus (Im.sp.) traverse the dorsal tegmentum to 

 reach the dorsal thalamus. More posteriorly the section passes through the gray of the superior 

 visceral-gustatory nucleus {nuc.vis.s.) and the junction of the body of the cerebellum {c.ch.) 

 with the auricle. 



Fig. 35. — Through the ventral borders of the dorsal habenular nucleus, nucleus pretectalis, 

 and tectum. Posteriorly it passes through the superior medullary velum, showing the decussa- 

 tion of the IV nerve roots, and through the body of the cerebellum dorsally of the cerebellar 

 commissure. Fibers of com. vestibulo-lateralis cerebelli are crossing at this level. Compare 

 1942, figures 78 and 79, cut in about the same plane, Weigert and Golgi. 



Fig. 36. — Through the com. posterior and the tectum at its widest part. In figures 35 and 

 36 the brachia of the superior and inferior colliculi are designated tr. tecto-thalamicus rectus 

 {tr.t.th.r.). 



