244 RALPH EDWARD SHELDON 
The olfactory crus is attached to the rostral end of the basal 
lobe by two systems of tracts, a medial and a lateral. The former, 
as in Amphibia, connects chiefly with the precommissural body 
(tractus olfactorius medialis) and in smaller measure with 
the dorso-medial part of the basal lobes termed primordium 
hippocampi in this paper, this relation being in principle similar 
to that of Amphibia and higher forms. The closely associated 
nervus terminalis and tractus olfactorius ascendens have been 
discussed in another connection. The tractus olfactorius lateralis 
connects chiefly with the lateral part of the basal lobe, the 
nucleus olfactorius lateralis and the nucleus pyriformis. These 
nuclei correspond ina general way with the dorso-lateral part of the 
amphibian hemisphere, or primordium of the lobus pyriformis. 
Like the palaeostriatum, they tend to move laterad away from the 
ventricular and toward the lateral surface of the basal lobe. 
In vertebrates with evaginated hemipheres the two dorsal 
parts (pars pallialis) lie on opposite sides of the lateral ventricle 
and in later phylogenetic stages become respectively the hippo- 
campus and the pyriform lobe. In the teleosts these parts are 
very imperfectly separated, especially at the rostral end of the 
basal lobe; here both are parts of a common secondary olfactory 
nucleus. Incident to the progressive enlargement of the:telen- 
cephalon without the evagination ofits walls, the thickened second- 
ary olfactory nucleus moves laterad, carrying with it the taenia, 
or line of attachment of the membranous roof, which accord- 
ingly becomes dilated laterally. (See figs. 126 to 134 illustrating 
the arrangement of these parts and the process of eversion.) 
It will be observed that the teleostean form has not been 
reached by a simple process of eversion of the whole wall such as 
that suggested by Mrs. Gage (’92; see fig. 185); for that would 
bring the primordium hippocampi, which borders the taenia in 
Amphibia, far ventro-laterally in the teleosts. This appears not 
to be the case, but a portion of the dorsal secondary olfactory 
nucleus retains its dorso-medial position with reference to the 
other massive structures, in spite of the lateral movement of the 
taenia. 'The movement in question is not, in fact, a simple lateral 
bending of the whole wall at the sulcus limitans telencephali, 
