SEPTUM, HIPPOCAMPUS, PALLIAL COMMISSURES 407 



They are then lost in the commissure itself and presumably go 

 to the hippocampus. Rostrally these fibers bend down over the 

 rostral border of the commissure and are made up from the fibers 

 of the fasciculus praecommissuralis (figs. 28, 35, 36). From the 

 stria medialis in its longitudinal course small bundles are given 

 off to the deep layer of the dentate fascia and the hippocampus 

 (fig. 36). These are in all probability fibers from the tuberculum 

 and other olfactory centers to the hippocampus. The fact that 

 the stria is separated from the fascia dentata by the fimbrio- 

 dentate sulcus at once suggests comparison with the fimbria in 

 reptiles. The stria medialis undoubtedly corresponds to a part 

 of the reptilian fimbria and it is important to notice that it 

 runs in the primordium hippocampi (septum) in the opossum 

 as in the reptile. The stria lateralis is represented in the opos- 

 sum by the longitudinal fibers in the stratum zonale of the hippo- 

 campus as Elliot Smith has stated. In addition to longitudinal 

 association fibers of the hippocampus, however, these bundles 

 include many fibers which come up from the tuberculum through 

 the rostral part of the primordium hippocampi. These are fibers 

 of the same category as those which make up the stria medialis; 

 both are olfacto-cortical fibers. These run near the lateral bor- 

 der of the hippocampus, while the stria medialis runs along its 

 medial border. Both the olfacto-cortical and the association fibers 

 are seen in the mole (fig. 48) but most of them end in the pre- 

 callosal hippocampus and primordium because the supracallosal 

 hippocampus is reduced to an indusium in the mole. In the 

 rabbit the stria medialis curves around the genu and is lost 

 among the fibers of the precommissural fasciculus rather far back 

 beneath the corpus callosiim. 



In the bear the indusium is rather large and maintains the 

 relations seen in the opossum. As seen in figures 76 and 77, 

 the stria medialis is separated from the hippocampus by a fim- 

 brio-dentate sulcus, the fascia dentata and hippocampus can be 

 distinguished and in the rudimentary hippocampus are seen both 

 the vestigeal alveus and the superficial stria lateralis. These 

 structures curve about the genu and are well preserved beneath 

 the callosum until the hippocampus expands into a broader band 

 reaching to the olfactory peduncle (figs. 77, 75). 



