418 C. JUDSON HERRICK 



nus septi), the two lateral parts are imperfectly separated by a 

 shallow ependymal groove which is the precursor of the fissura 

 endorhinalis, and the dorso-medial part is sharply inflected from 

 the dorso-medial angle to the taenia fornicis. The pars dorso- 

 medialis becomes the primordium hippocampi of the adult. 



The rostral ends of all four parts of the hemisphere are reached 

 by fibers from the olfactory bulb and fibers of the tractus olfacto- 

 rius dorso-lateralis follow the whole length of the pars dorso- 

 laterals and reach the posterior pole. The basal forebrain bun- 

 dle contains two chief components which characterize respectively 

 the ventro-lateral and the ventro-medial parts of the hemisphere, 

 as seen best in the adult frog. The mingling of these compo- 

 nents in urodeles is correlated with the imperfect separation of the 

 two ventral parts of the hemisphere. The lateral and medial 

 forebrain tracts can, however, be distinguished in Cajal prepara- 

 tions by the presence of much coarser fibres in the former (fig. 3). 

 The medial forebrain tract connects chiefly with the hypothala- 

 mus, the lateral with the thalamus and mid-brain. Both de- 

 cussate partially in the anterior commissure (fig. 5). 



The taenia fornicis is accompanied by a mixed fiber tract whose 

 composition varies in different parts and which I term the fimbria 

 complex. At the rostral end it receives the dorsal component 

 of the tractus olfactorius medialis (figs. 1 and 2) and comparison 

 with the adult and with Anura suggests that here also it probably 

 contains elements of the primordial columna fornicis system pass- 

 ing rostrally of the interventricular foramen and anterior com- 

 missure between the primordium hippocampi and the pars ventro- 

 medialis. Farther back this tract contains fibers for the com- 

 missura pallii anterior (corn, hippocampi), others for the stria 

 medullaris and perhaps thalamic connections, all of which leave 

 the primordium hippocampi in the region of the posterior pole 

 caudal to the foramen interventriculare (see pp. 427 ff.). 



The dorso-medial and dorso-lateral parts of the hemisphere con- 

 verge at the posterior pole, where their distinctive character- 

 istics are lost. This applies to the adults also of both Urodela 

 and Anura. 



The relations of telencephalon and diencephalon are difficult 



