440 C. JUDSON HERRICK 



is relatively larger than in the adult and increases rapidly in size 

 farther caudad. It lies ventrally of the sulcus diencephalics 

 medius, is the equivalent of the eminentia thalami of urodeles 

 and is directly continuous, as recognized by Gaupp ('99, p. 82), 

 with the pars ventralis thalami (pars medialis, Gaupp). Its 

 fiber connections I have not determined with certainty in the 

 frog, but its uniform position at the union of the fimbria complex 

 and the stria medullaris suggests that it is related to both of these 

 tracts (see especially fig. 33), as indeed I find to be the case in 

 reptiles. In the urodeles numerous fibers pass from the equiva- 

 lent structure (eminentia thalami) into the stria medullaris (fig. 

 18). The fibers of the tractus cortico-habenularis medialis pass 

 directly through it and some of these fibers may end here. The 

 same is true of fibers of the tractus olfacto-habenularis from the 

 preoptic nucleus. 



Some of my preparations of adult frog brains by the silver re- 

 duction method of Ram6n y Cajal show very delicate fibers pass- 

 ing between this nucleus and the commissura pallii anterior. 

 These appear to be dendrites of the cells of the nucleus and col- 

 laterals of the commissural fibers. Golgi preparations of adult 

 Necturus show clearly short collaterals from the commissural 

 fibers coming into relation with the cells of this nucleus. This 

 indicates that the nucleus constitutes, in part at least, a station 

 for nervous impulses passing between the primordium hippocampi 

 and the habenula. The fibers from the commissura pallii ante- 

 rior (com. hippocampi) thus constitute a tractus cortico-habenu- 

 laris medialis cruciatus, with a synapse interpolated in this path 

 at the supracommissural nucleus. The crossed and uncrossed 

 path together, in this case, are strictly comparable with the trac- 

 tus cortico-habenularis of reptiles and mammals save that in 

 Amphibia they pass (like the commissura hippocampi itself) 

 dorsad and caudad of the interventricular foramen to reach the 

 stria medullaris, whereas in Amniota the path goes rostrad and 

 ventrad of the foramen. We shall find the relations of these 

 tracts in reptiles very instructive in this connection. (See p. 461.) 



The relations of the fimbria complex, including the commis- 

 sura hippocampi, to the stria medullaris at this point areessen- 



