THE AMYGDALA IN AMPHIBIA » 233 
the dorsal border of the chiasma ridge, which is termed the nucleus 
of this tract. Our preparations indicate that this tract includes 
both ascending and descending fibers in both Anuraand Urodela. 
Free terminal arborizations are abundant at both ends of the 
tract and in urodeles axons of neurons of its hypothalamic nucleus 
are directed dorsally into it. 
The nucleus of the olfactory projection tract is not clearly 
defined in cell preparations (figs. 12, 20, 21), but in Golgi prepara- 
tions of Rana it is seen as a horseshoe-shaped mass of dense 
neuropil occupying the most dorsal part of the chiasma ridge 
immediately caudad of the decussating chiasma fibers and 
extending across the median plane (figs. 22, 23). In Anura it 
appears to occupy the extreme dorsal border of the chiasma 
ridge, but in urodeles it lies considerably farther caudad and 
ventrad in the hypothalamus. We have no satisfactory impregna- 
tion of its neurons in the Anura. 
Following the dorsal olfactory projection tract spinalward from 
the amygdala (figs. 7 to 12), its fibers are seen to assemble from 
the entire caudal part of this structure on the medial border 
of the lateral forebrain bundle, to accompany this bundle for 
Fig. 19 Section through the olfactory and vomeronasal formations of the 
olfactory bulb and the amygdala. The ventrolateral olfactory tract, which 
curves slightly dorsally in its course from the vomeronasal formation to the 
amygdala, does not lie in the plane of this section. On the right side it is 
sketched in by projection from the three adjacent sections farther dorsal. In 
the region of the vomeronasal formation the stratum moleculare is absent and 
the mitral cells are more or less mingled with the granule cells. 
Fig. 20 The section passes considerably farther ventral than that shown in 
figure 19, below the level of the interventricular foramen. The amygdala lies 
for the most part dorsally of this level. From its ventral border the olfactory 
projection tract passes backward and medialward to its nucleus at the level of 
the chiasmaridge. The brain being small and the sections thick, almost the whole 
length of this tract lies in the plane of a single section. At its caudal end it dips 
ventralward for a short distance. The commissure between the amygdalae 
and the decussation of the lateral forebrain bundles are sketched in from the 
adjacent section ventrally. 
Fig. 21 Three sections ventrally of the plane of figure 20, passing through 
the dorsal border of the chiasma ridge. The nucleus of the olfactory projection 
tract lies mostly dorsally of this plane, probably including some neurons in the 
position indicated (nwuc.o.p.tr.) at the level of this section. Its boundaries are 
nowhere clearly defined in this series, 
