246 RALPH EDWARD SHELDON 
position during the lateral eversion of the remainder of this 
nucleus. The adult configuration is such as to suggest that the 
nucleus dorsalis is homologous with the amphibian primordium 
hippocampi and the sulcus limitans telencephali with the fissura 
limitans hippocampi of Herrick (fissura arcuata of Gaupp). 
The latter homology is however, manifestly incomplete, for the 
fissura limitans hippocampi is a total fissure involving the whole 
wall of an evaginated hemisphere, while the teleostean sulcus 
limitans is an ependymal groove within the ventricle of the telen- 
cephalon medium. The two sulci in question separate homol- 
ogous parts of the brain and are as nearly homologous as the 
topographic relations of these two types of telencephalon permit. 
Some justification may be found for the homology of the 
nucleus olfactorius dorsalis with the primordium hippocampi of 
Amphibia, although the apparent resemblance in position is an 
argument rather against it than for it. It must not be for- 
gotten that the nucleus dorsalis occupies a dorso-median position 
below the telencephalic ventricle, not above it, as in Amphibia. 
In the process of eversion, to which reference was made above, the 
whole of the dorsal nucleus might be expected to follow the taenia 
in its lateral movement. The fact that a part of this nucleus 
retains its position at the dorso-medial border of the basal lobe 
has been already explained as due to its connection with the trac- 
tus olfactorius dorso-medialis. This is a primary connection of 
the primordium hippocampi; cf. fig. 125 with C. J. Herrick (710 b), 
figs. 72, 73, 83 and 84, the nucleus olfactorius dorsalis or primor- 
dium hippocampi of the teleost being the functional equivalent 
of Herrick’s dorso-medial ridge in spite of its position far removed 
from the taenia. Nevertheless, the nucleus dorsalis shows few 
other resemblances with the primordium hippocampi. It has 
not been shown to receive large numbers of olfactory fibers of the 
third or higher orders; it sends very few fibers to the anterior 
commissure complex to form a commissura hippocampi and no 
clearly defined columna fornicis fibers appear to arise from it, 
though possibly the medial forebrain bundle may contain fibers 
of this type. 
