196 Journal of Comparative Neurology. 



ventral wall of the cerebrum, which has been homologized with 

 the striatum, and there most of its fibers terminate. Some of 

 the fibers decussate in the precommissure as before mentioned, 

 and a number extend into the olfactory lobes. These olfactory- 

 fibers divide into two groups, one of which passes cephalad to 

 the olfactory lobe in the ventral wall of the cerebrum, while the 

 other bundle passes gradually laterad, dorsad and then mesad 

 to the extreme cephalic portion of the mesal wall. These are 

 probably those mentioned and figured by Osborn in the dorsal 

 aspect of the brain of Siren. 



In the cinerea of the lateral wall just caudad of the olfac- 

 tory glomeruH numbers of myelinic fibers appear which pass 

 dorso-cephalad to the mesal wall. Whether or not these con- 

 stitute a tract connecting the lateral and mesal walls of the 

 olfactory lobe, or come cephalad from the peduncles in the cin- 

 erea, could not be determined.^ 



Upon the ventral surface of the cerebrum several small 

 fascicles of amyelinic fibers go caudad from the olfactory lobes 

 to the region immediately cephalad of the mesencephalic groove 

 ( mammillary region ? ) where they turn mesad and disappear. 

 They undoubtedly represent a diencephalic olfactory tract 

 and are shown in the figures as olf. tr. Some of these fibers 

 decussate below the precommissure, others do not. They are 

 shown in Figures 27 and 36 and in the transections through 

 the regions they traverse. 



^Since the above was written has appeared a paper by G. Elliot Smith in the 

 Anatomischer Anzeiger (Vol. X, No. 15, pp. 470-474) on " The Connection between 

 the Olfactory Bulb and the Hippocampus," in which is discussed a direct con- 

 nection in the mesal wall, of the fascia dentata with the olfactory lobes, which 

 was found in the Marsupial Brain (Platypus), and believed by him to be repre- 

 sented in the brain of the higher mammals by the striae Lancisii. Should that 

 portion of the mesal wall in the amphibian brain to which the fibers of the 

 dorsal commissure are distributed be shown to constitute a representative of 

 the hippocampal region of the mammalian brain, it is suggested that the above 

 described fibers might in that case represent a direct connection between the 

 region of the olfactory glomerules and the mesal wall. In that event, however, 

 the olfactory lobes would be almost entirely lateral, being represented in the 

 mesal wall only by the extreme cephalic portion. 



