214 RALPH EDWARD SHELDON 
a fourth commissure, entirely unmedullated, connecting the 
ventral parts of the two nuclei pyriformes, and here termed the 
commissura hippocampi, pars posterior. Its fibers are closely 
intermingled with those of the decussating tractus olfactorii 
mediales, partes laterales, distinguishable in Weigert preparations 
owing to their lack of medullary sheaths (fig. 138). See also 
Goldstein, Taf. 11, fig. 7; Goldstein terms this the commissura 
olfactorii internuclearis. This commissure is shaped like a bow, 
with either end bent caudally to terminate inthe nuclei pyriformes 
(figs. 36, 37, 55). This is the hippocampal commissure of C. L. 
Herrick, probably also the commissura interolfactoria of Kappers. 
This commissure offers points of resemblance with the fibers of the 
commissura dorsalis, which connect the two occipital poles in the 
frog and with a part of the commissura pallii of Kappers in the 
frog. 
It will be noticed that.the anterior commissure complex con- 
tains two bundles connected with the primordium hippocampi, 
and one with the nucleus pyriformis, all of which are probably 
represented in the commissura dorsalis, or commissura hippocampi 
of amphibians. The morphological significance of the regions 
thus connected will be considered later. 
These comprise all of the connections of the basal lobes except- 
ing those bringing them into relation with the diencephalon, 
together with a few praethalamic connections which will be taken 
up later. 
c. Diencephalic connections 
(1) The tractus olfacto-habenularis. In 1892 Edinger described 
for selachians a tract between the basal lobes and the ganglia 
habenularum which he called the tractus ganglii habenulae ad 
proencephalon, stating, however, the possibility that its fibers 
might run in the opposite direction. Such a connection was also 
indicated by C. L. Herrick, in the same year under the name of 
taenia thalami. All recent writers have observed these fibers, 
and have shown that they are largely ascending, from the basal 
lobes to the habenular ganglia of the epithalamus. Catois 
traces the fibers of his tractus olfacto-habenularis from the caudal 
