432 C. JUDSON HERRICK 



one of which is the subhabenular sulcus which curves dorsally 

 around the caudal end of the habenula. The other segment be- 

 gins under the caudal end of the habenula and extends backward 

 through the whole remaining length of the diencephalon. The 

 tissue dorsally of it apparently corresponds with the "post- 

 habenulare Zwischenhirngebiet" described by Goldstein ('05) in 

 teleosts. Its morphology is obscure. The pars dorsalis thalami 

 does not extend as far rostrad as the pars ventralis. Accord- 

 ingly, the sulcus medius in the rostral part of its course (figs. 18 

 and 19) separates the pars ventralis (eminentia thalami) from the 

 epithalamus instead of from the pars dorsalis thalami, as farther 

 caudad (see fig. 22). The sulcus diencephalics dorsalis is inter- 

 rupted by the commissura posterior, behind which the tectum 

 mesencephali for a short distance lies dorsally of the thalamus 

 in the same relations as the post-habenular intermediate region 

 does farther forward (fig. 21). A short distance farther caudad 

 the pars dorsalis thalami also disappears or is merged with the 

 tectum mesencephali and the pars ventralis thalami passes over 

 into the pedunculus cerebri region under the tectum. 



The sulcus limitans extends forward from the midbrain into 

 the preoptic recess, its whole diencephalic extent being preserved 

 in the adult Amblystoma (see fig. 22) . In the adults of some other 

 amphibians it seems to be obliterated where it crosses the qaudal 

 end of the pars ventralis thalami. In fig. 22, which is drawn from 

 sagittal sections of adult Amblystoma, there are seen two short 

 sulci running ventrally from the interventricular foramen across 

 the preoptic nucleus. The more rostral one follows the caudal 

 border of the anterior commissura ridge and is the ventral part 

 of Kupffer's sulcus interencephalicus anterior, as we found it in 

 the 17 mm. larva. The other vertical sulcus divides the preoptic 

 nucleus into rostral and caudal portions (figs. 18 and 19), which 

 I shall term the pars anterior and pars magnocellularis of the pre- 

 optic nucleus. The latter is homologous with the nucleus mag- 

 nocellularis of fishes and is intimately related with the corpus 

 striatum complex and the rostral end of the pars ventralis thalami. 

 The tractus olfacto-habenularis medialis arises chiefly from this 

 nucleus, the tractus olfacto-habenularis lateralis from the rostral 



