362 THE BRAIN OF THE TIGER SALAMANDER 



the figure. The details of this optic connection have been pubHshed ('42, p. 235). The fibers of 

 f . tegmentaHs profundus seen at the right are ascending from their decussation in the ventral 

 commissure to spread superficially over the lateral aspect of the isthmic tegmentum. Most of 

 these fibers belong to the brachium conjunctivum. 



Fig. 73. — Section more medially, showing details of the origin of the f. retroflexus from the 

 habenula. X 50. The drawing is a combination of three adjoining sections. Only the thicker 

 axons of the fasciculus are here impregnated. These surround a dense fascicle of thinner un- 

 stained fibers. The fibers here impregnated arise from neurons of the habenula, from others 

 more posteriorly in the pars intercalaris, and probably also from some of the impregnated 

 neurons of the pars dorsalis thalami. None of these stained fibers reach the interpeduncular 

 nucleus. They spread out in the alba of the posteroventral part of the peduncle, some turning 

 forward into area ventrolateralis pedunculi. The dendrites of the impregnated neurons of the 

 dorsal thalamus extend dorsally among terminals of tr. tecto-thalamicus rectus and also for 

 long distances posteroventrally, accompanying the f . retroflexus into the area of the primordial 

 geniculate bodies (pp. 221, 238). Sections taken more laterally show abundant impregnation of 

 axons from this group of cells which enter tr. thalamo-frontalis (fig. 72). 



Figures 74 to 78. — Five sagittal sections of the adult brain, illustrating the composition of 

 the stria medullaris thalami (p. 256 and fig. 20). X 37. The sections were prepared by the 

 reduced silver method of Cajal and cut at 10 n slightly oblique to the sagittal plane, with the 

 dorsal and rostral sides more lateral (compare "36, figs. 17-79, where the dorsoventral obliquity 

 is in the reverse direction). In these sections the thickest axons, both myelinated and unmyeli- 

 nated, are black, and the thinner fibers range through gray to brown or yellow, so that com- 

 ponents of the stria are well dififerentiated. 



Fig. 74. — This cuts through the di-telencephalic junction near its lateral border, passing 

 through the olfacto-peduncular tract below, and above this through the dorsal and ventral 

 fascicles of the lateral forebrain bundle. The artery (r.h.m.) lies in the floor of the stem-hemi- 

 sphere fissure. Here four components of the stria medullaris converge, two of them- — tr. olfacto- 

 habenularis anterior and lateralis — passing up from the ventral surface externally of the lateral 

 forebrain bundles. 



Fig. 75. — In the region of the stem-hemisphere fissure the section passes medially of the 

 lateral forebrain bundles, showing the connection of tr. olfacto-habenularis medialis and tr. 

 septo-habenularis with the stria. Ventrally the plane of section is not far from that of figure 

 103; dorsally it is much more lateral. 



Fig. 76. — At this level tr. cortico-habenularis medialis enters the stria and ascends as its 

 mo.st rostral member. All components of the stria are distributing fibers in the habenular 

 neuropil, posteriorly of which several of the tracts retain their identity. Fibers of tr. habenulo- 

 thalamicus which recurve spinalward over the gray of the dorsal thalamus have been seen to 

 connect only with the ventral habenular nucleus. This tract includes also thalamo-habenular 

 fibers. The boundary of the gray of the eminentia thalami is marked by a broken line. 



Fig. 77. — A large proportion of the fibers of all components are here dispersed in the habenu- 

 lar neuropil. A residue of fibers is accumulated posteriorly in a commissural bundle, within 

 which the following components can be identified: tr. cortico-habenularis lateralis and medialis, 

 tr. olfacto-habenularis anterior, tr. amygdalo-habenularis. 



Fig. 78. — In this section, 300 ^ from the mid-plane, the limits of the gray of the dorsal 

 habenular nucleus (corresponding with the medial nucleus of mammals) and of the pretectal 

 nucleus are marked by broken lines. Most of the habenidar neuropil has disappeared. Some 

 fibers from this residue enter the habenular commissure, but most of the crossing fibers are 

 derived from recognizable tracts. The thickest fibers cross at the anterior end of the commis- 

 sure. These apparently are derived chiefly from tr. amygdalo-habenularis, with additions from 

 other components. The thinner fibers of the commissural bundle include clearly some residue 

 of tr. cortico-habenularis lateralis and medialis and tr. olfacto-habenularis anterior. 



Figures 79 and SO.— Two adjoining obliquely sagittal Golgi sections of the adult brain, illus- 

 trating some components of the interpeduncular neuropil. In this specimen the finest axons are 

 richly impregnated, especially the deep neuropil of the gray substance, which is continuous 

 throughout the tectum, peduncle, and dorsal, isthmic, and bulbar tegmentum. In the area illus- 

 trated it receives fibers from the fields dorsally and anteriorly, and from it axons descend to the 



