MORPHOLOGY OF THE FOREBRAIN 431 



in these specimens than in the frog. The lateral forebrain tract 

 is the great conduction path between the lateral parts of the hemi- 

 spheres and the thalamus. 



As is well known, the choroid plexuses of the region are very 

 complex in adult urodeles ; but their development in Amblystoma, 

 Necturus (Warren, '05) and Salamandra (KupfTer, '06, p. 171) 

 shows that the lateral plexuses, median telencephalic plexus 

 (auliplexus, of Kingsbury, '95, fig. 4, and Fish, '95; fig. 3) and 

 paraphysis sensu stricto develop from the telencephalic lamina 

 of the velum transversum in the typical manner, while the 

 diencephalic plexus arises from the caudal lamina of the velum. 

 Fig. 16 is taken at the point of union of the median telencephalic 

 and diencephalic plexuses, i.e., at the dorsal boundary between 

 telencephalon and diencephalon. The eminentia thalami is 

 developed wholly caudal to this level. The di-telencephalic 

 boundary curves downward and backward rostral to this emi- 

 nence along the line of the sulcus ventralis in figures 17 to 21 to 

 terminate far caudad behind the optic and post-optic commissure 

 ridge. This very anomalous relation grows out of the exaggerated 

 size of the preoptic and supraoptic nucleus in the telencephalon 

 medium of urodeles. 



The plan of the diencephalon appears with diagrammatic sim- 

 plicity in cross sections of the adult brain, where the embryonic 

 diencephalic flexure no longer complicates the matter. The three 

 longitudinal sulci found in the 17 mm. larva (see p. 419) are pre- 

 served. The sulcus diencephalicus ventralis passes backward 

 from the interventricular foramen and separates the preoptic 

 nucleus and hypothalamus from the thalamus. 



The sulcus medius passes backward from the foramen and sep- 

 arates the thalamus (medithalamus) into dorsal and ventral parts. 

 It becomes less distinct farther caudad and, as in the larva, joins 

 the sulcus limitans. The rostral end of the pars ventralis thai- 

 ami is somewhat enlarged and separated from the remainder by a 

 wide groove. This is the eminentia thalami (figs. 17, 18 and 22) 

 which is larger in young larvae than in the adult. 



The sulcus diencephalicus dorsalis separates the epithalamus 

 from the thalamus. It is divided into two segments, the rostral, 



