OLFACTORY CENTERS IN TELEOSTS 243 
the basal lobe the ventro-medial column appears in its primitive 
relations, forming here the nucleus medianus of the precommis- 
sural body. Passing caudad the nucleus medianus bifurcates 
at- the anterior commissure into the dorsal pars supracommis- 
suralis and the ventral pars commissuralis or commissure bed. - 
The latter is directly continuous with the nucleus preopticus, 
which in turn grades almost insensibly into the hypothalamic 
nuclei. The pars supracommissuralis becomes continuous cau- 
dally withthe nucleus intermedius. The cells of the latter nucleus 
likewise grade over into those of the nucleus posthabenularis and 
habenula, but this connection is probably secondary, as will be 
brought out later. 
The other diencephalic columns are interrupted at the level 
of the velum transversum save for the fiber tracts of .the basal 
forebrain bundles. Dorsal to the ventro-medial column lies the 
primordium hippocampi rostrally, immediately above the corpus 
precommissurale. This, the dorso-medial column of Herrick, is 
probably the telencephalic extension of the epithalamic habenula 
and nucleus posthabenularis of the diencephalon. 
The nucleus entopeduncularis probably belongs to the same 
column as the pars ventralis thalami, the pars ventro-lateralis 
of Herrick, which expands rostrally to form the palaeostriatum. 
In the evaginated hemispheres of the Dipnoi and Amphibia the 
striatal complex is carried outward into the ventro-lateral wall 
of the hemisphere vesicle. In teleosts the wall as a whole does 
not evaginate in this way; but the striatum complex, with the 
associated lateral forebrain tract, moves outward within the 
solid basal lobe away from the ventricular surface and toward the 
lateral surface of the brain, a movement which has been carried 
to a greater extreme in the ‘somatic area’ of elasmobranchs 
(Johnston, ’11). The precommissural body and the palaeostria- 
tum are tobe regarded as extensions of the hypothalamus and ven- 
tral part of the thalamus respectively and, therefore, as equiva- 
lent to the pars basalis, or pars subpallialis, of the amphibian 
hemisphere. The remainder of the basal lobe is the extension 
of the epithalamus and dorsal part of the thalamus and, there- 
fore, is the equivalent of the pars pallialis of the amphibian brain. 
