CELL MASSES IN THE FOREBRAIN 409 
complex on the other hand. In the ichthyopsid brain where 
the temporal pole has not yet been. formed, the continuity of the 
corresponding regions is broad and direct. The size and func- 
tional importance of this connection in reptiles and mammals 
is of great significance for the explanation of the evolution of the 
temporal pole and the general_pallium. 
LOBUS PYRIFORMIS 
As already indicated the pyriform lobe forms a somewhat 
prominent ridge along the dorso-lateral surface of the hemi- 
sphere, extending from the olfactory peduncle into the caudal 
pole. It is separated from the general pallium dorsally by the 
fissura rhinalis. Rostrad this fissure runs obliquely mesad and 
joins the peduncular groove or constriction as it bends down into 
the medial wall. Caudally the fissura rhinalis presents consider- 
able individual variation in its depth and length. Usually it 
fades away at about the middle of the hemisphere (fig. 1) so that 
there is no gross boundary line between the caudal part of the 
pyriform lobe and the general pallium. In the rostral part of the 
hemisphere a slight sulcus endorhinalis approximately marks the 
boundary between the pyriform lobe and the area occupied by 
the tuberculum and corpus striatum (figs. 22 to 26). The caudal 
continuation of this sulcus becomes much deeper between the 
pyriform lobe and the striatal area (fig. 1) and bends down 
between the striatal area and the amygdaloid prominence. At 
the point of bending is the deepest part of this groove and from 
this point the: amygdaloid fissure extends caudad as above 
described. 
The pyriform lobe consists of the lateral olfactory tract and 
the special gray matter accompanying the tract. Sections 
through the middle or rostral part of the lobe (figs. 19, 25) show 
that it consists of a superficial fiber layer and a deeper plate of 
cells and that it is everywhere very clearly and sharply separated 
from. the border of the pallium, the dorsal ventricular ridge and 
the lenticular nucleus by a cell-free zone. This cell-free zone is 
more sharply marked than any other in the brain. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, NO. 5 
