THE AMYGDALA IN AMPHIBIA 253 
Necturus and Amphiuma 
In Necturus maculosus the relations are broadly similar to 
those of Amblystoma, though there are important differences 
which have not been fully worked out. There is an accessory 
olfactory bulb very poorly differentiated from the rostral portion 
of the bulb. The fibers of the lateral olfactory tract arising from 
it are distributed to the entire lateral wall of the hemisphere 
mingled with those from the rostral part of the bulb. There is 
no separately differentiated amygdala, but a very clearly defined 
dorsal olfactory projection tract passes between the ventro- 
lateral nucleus of the hemisphere and the hypothalamus, as in 
Amblystoma. 
In Amphiuma means the relations are much as in Necturus. 
The large olfactory bulb is fairly uniformly developed in the 
rostral third of the lateral wall of the cerebral hemisphere. The 
caudal part of it receives the more lateral bundles of fibers of the 
olfactory nerve, but there is no clearly defined accessory bulb. 
Our material does not permit determination of the peripheral 
relations of the fibers related with the caudal end of the bulb, 
nor can the unmyelinated fibers of the lateral olfactory tract 
be analyzed. 
The dorsal olfactory projection tract is large and can readily 
be followed in horizontal sections for its entire course. Its 
hypothalamic nucleus lies very far ventrally at the caudal border 
of the chiasma ridge. The fibers of the tract enter the nucleus 
in many small fascicles, most of which decussate as the most 
caudal component of the postoptic commissure complex and then 
spread widely caudolaterad in the deepest part of the stratum 
album of the infundibulum. 
Following the fibers of the olfactory projection tract forward 
from their nucleus, they are seen to converge into one or several 
compact fascicles which pass dorsalward along the caudal border 
of the chiasma ridge, then turn slightly lateralward and abruptly 
forward embedded among the fibers of the lateral forebrain 
bundle. Their further course can readily be traced into the 
neuropil of the ventrolateral nucleus of the cerebral hemisphere, 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 33, No. 3 
