FOREBRAIN MORPHOLOGY AO 
seen in the sections as a row of white points (fig. 6). Thus the 
primordial cortex here is practically differentiated as an uninter- 
rupted cortical layer passing from one side of the brain roof over 
to the opposite. Examining this layer with attention, one cannot 
avoid observing that the extreme lateral part of it is somewhat 
different from the remaining. Its cells are a little larger, less 
densely packed and assume a paler color than the other cortical 
cells. Jn this early stage the differentiation of the pyriform cortex 
thus 1s begun. ‘This pyriform lobe is quite dorsal in position and 
dorsal also to the olfactory prominence (bulbus olfactorius). 
Lateral to the pyriform lobe a relatively cell-free space represents 
an obsolete zona limitans, lateral to which the olfactory bulb 
rudiment is situated. 
It is of some importance to observe that the primordial cortex 
at one point is continuous with the ventricular layer, viz., the 
dorsolateral part, medial to and below the pyriform lobe, where 
cell masses are streaming out from the ventricular layer pressing 
the primordial cortex against the brain surface and partially 
coalescing with it. This process represents the first stage of the 
formation of a new cortical layer, which begins below the medial 
part of the pyriform cortex and from here extends medially, 
forming what I will name the general pallium. 
In the subpallial parts of the brain the cortex of the tuberculum 
olfactorium is nearly quite disengaged from the ventricular sheet. 
The bulbar nuclei are in this stage under formation from the ven- 
tricular layer at the lateral part of the ventricle inside the olfac- 
tory bulb rudiment (the most lateral part of the forebrain). 
Between these bulbar nuclei and the upper border of the tuber- 
culum olfactorium cortex there is found a diffuse, in the lateral 
part rather dense, mass of cells, derived from the underlying 
ventricular sheet. This cell-mass, I think, represents a lateral 
olfactory nucleus. 
3. Stage of 3.7-cm. body length (measured after fixation in Carnoy’s 
fluid). In this stage the pyriform lobe is separated from the 
remaining primordial cortex layer, excepting in the foremost 
part of the brain, where the two cortex components seem to flow 
together. The part of the ventricular layer from which the 
