FOREBRAIN MORPHOLOGY 409 
olfactorium cortex have been replaced by the ‘area somatica’ 
of Johnston(?), a cortex-like structure which in the form of a ~~ 
covers the brain medially. The band of scattered cells in fore- 
going sections between the medial extremities of the tubercula 
olfactoria now is found below the area somatica. In preceding 
sections there is a more densely aggregated group of cells (n.t.) 
at the medial end of the olfactory cortices. More backwards 
‘ these condensations are found more lateral and as the “~~ - 
shaped area somatica makes its appearance in the series this 
cell-heap lies below the lateral end of the same area. This cell 
formation that accompanies and emigrates from the inner part 
of the tuberculum olfactorium in Cajal preparations has been 
found to give origin to taenia fibers. It is the nucleus taeniae, 
hitherto not clearly demonstrated in selachians. 
7. Stage of 6.5-cm. body length (measured after preservation in 
formolalcohol). Cross-sections. In this stage no essential 
changes in the structure of the telencephalon are to be noted. 
The general arrangement is the same as in the preceding stage, 
but the different parts are more accentuated than before. Thus 
the hippocampal rudiment has grown much more distinct with 
more densely packed cells, especially in its frontal part (fig. 17 
A). It now has taken on the aspect of an ordinarily constructed 
cortical layer. The two hippocampal cortices meet each other 
above the neuroporic recess. 
The medial thickening of the general pallial cortex is greater 
than before (fig. 17 B) and just at the level of the basis of the 
processus neuroporicus it joins in the medial line the correspond- 
ing part of the opposite side. Here the hippocampal cortex is 
no longer present. 
The pyriform cortex is not distinctly delimited from the 
general pallial cortex. The zona limitans medialis is absent. 
The lateral zona sometimes is present, sometimes absent. 
The nucleus olfactorius lateralis is more distinct (fig. 17, 
n.olf.l.) than in the preceding stage. Other structures are as 
before, but somewhat more pronounced. 
8. Stage of 8-cm. body length (measured after fixation in 10 per 
cent formalin). Cross-sections. The definitive arrangement of 
