410 J. B. JOHNSTON 
The outer surface of the lobe is covered by a continuous sheet 
of fibers of the lateral olfactory tract. These arise in larger 
part from the lateral wall of the olfactory bulb and in smaller 
part from the dorsal and medial wall. The former fibers enter 
the extreme rostral end of the pyriform lobe on the lateral sur- 
face of the peduncle; the latter cross from the medial to the 
lateral side in the peduncular groove on the dorsal surface and 
join the former fibers to make up the common tract (figs. 55, 56). 
Just behind the peduncular constriction the pyriform lobe 
appears to thicken rapidly. This thickening forms a conspicu- 
ous rounded prominence on the dorso-lateral surface of the 
hemisphere (figs. 26, 5). The arrangement and relations of the 
cell masses in this prominence show at once that it is made up 
of two parts. The surface layer of cells belongs to the pyriform 
lobe and is no thicker here than elsewhere. The elevation here 
is due to the deep layer of cells which is the thickened lateral 
border of the general pallium (figs. 24, 25, 26). This is indeed a 
lateral extension of the dorsal pallial thickening, which lies 
beneath the pyriform lobe as the lateral border of the pallium 
does throughout the rostral two-thirds of the lobe. The pyri- 
form lobe, then, is not actually thickened but is merely bulged 
out by the thickening of a pallial formation beneath. 
The majority of cells in the pyriform lobe are large multipolar 
cells with large dendrites. In regard to this a comparison of the 
pyriform lobe with other parts of the forebrain reminds one of 
the comparison between Deiters’ nucleus and adjacent nuclei 
in the medulla oblongata. The cells are noticeably larger’in the 
rostral half of the lobe than in the caudal, the largest cells and 
the greatest proportion of large cells being found just behind the 
prominence above mentioned. In the caudal part the cells 
become distinctly smaller and where the lobe broadens out to 
form the lateral wall of the ventricle, the cells take on pyra- 
midal forms much like the cells of the eens pallium or the 
hippocampus. 
Throughout the rostral half of the pyriform lobe small cells 
are almost wholly confined to its ventral portion (figs. 19, 25, 40). 
These small cells extend somewhat below the sulcus endorhinalis, 
