THE HABENULA AND ITS CONNECTIONS 259 



p. 212). In Necturus the arrangement of these tracts is somewhat 

 different ('336, pp. 210-13). 



5. Tractus cortico-habenularis lateralis. These unmyelinated 

 fibers, as just described, pass from the piriform and dorsal pallial 

 areas in company with those of no. 4 (fig. 20) to the habenula, where 

 the majority of them decussate in the com. superior telencephali. 

 Although there is no differentiated cortex in the amphibian brain, 

 this tract is so evidently homologous with the one so named in mam- 

 mals that this name is preferable to Ariens Kappers' term, "tr. 

 olfacto-habenularis lateralis," because the latter term is commonly 

 applied to a different tract, no. 2 of the present list. In my paper of 

 1910 (p. 428) the tr. olfacto-habenularis anterior was not recognized 

 as a separate entity but was regarded as a forward extension of the 

 tr. olfacto-habenularis from the preoptic nucleus. This usage has 

 some justification in cyclostomes and other most primitive verte- 

 brates and is still employed by some authors, but the distinction 

 between the fibers which arise from the preoptic nucleus and those 

 from the hemisphere is significant and should be recognized in the 

 nomenclature. In most species tr. cortico-habenularis lateralis is well 

 defined. To avoid confusion, the terms "tr. olfacto-habenularis 

 lateralis et medialis" should be restricted to fibers which enter the 

 stria medullaris between the anterior commissure and the optic 

 chiasma, arising either in the preoptic nucleus or as collaterals from 

 the medial forebrain bundle. 



6. Tractus amygdalo-habenularis. These are thick fibers, some of 

 which are myelinated, passing from the gray of the amygdala to the 

 habenula. Some of them may connect farther forward with the pri- 

 mordial corpus striatum — tr. strio-habenularis. These fibers ascend 

 in the stria between nos. 5 and 8, and many of them end in the 

 habenular neuropil (figs. 31-34, 74-78; '27, p. 302 and figs. 13, 14). 

 As they approach the habenular commissure, these thick fibers 

 mingle with those of the medial cortico-habenular tract, and these 

 components can be separated only in electively impregnated speci- 

 mens. In one such preparation of adult Amblystoma (no. 2257) the 

 sections are inclined about 45° to the sagittal plane and the tr. 

 amygdalo-habenularis is heavily and electively impregnated on both 

 sides. The only other component of the stria stained is a small num- 

 ber of fibers of tr. cortico-habenularis medialis on one side only. The 

 large tract from the amygdala is clearly followed through the com- 

 missure to the amygdala of the opposite side. 



