SEPTUM, HIPPOCAMPUS, PALLIAL COMMISSURES 443 



Fig. 28 Opossum, transverse section a short distance rostral to the anterior 

 commissure. Note that the nucleus parolfactorius medialis is imbedded in the 

 precommissural bundle. Note the continuity of the fascia dentata and the hip- 

 pocampus and the close connection of the primordium with both. The rostral 

 limb of the anterior pallial commissure contributes most of the fibers to the 

 alveus at this level. 



Fig. 29 Opossum, transverse section through the neuroporic recess. Here is 

 seen the typical fully developed hippocampal formation with the primordium 

 transversed by the anterior pallial commissure. All above the neuroporic recess 

 belongs to the pallium. The commissure was thicker in the Weigert specimen 

 than in the other. For the stria medialis Lancisii compare figure 37. 



Fig. 30. Opossum, transverse section through the interventricular foramen 

 and at the caudal border of the anterior pallial commissure. The fusion of the 

 hippocampus with the overlying dorsal wall seen in the right half of the figure 

 occurs frequently. In these fused places fibers seem to pass from the corona 

 radiata into the alveus. These would probably be regarded as corpus callosum 

 fibers. Of the three bundles constituting the stria terminalis the middle one 

 enters the anterior commissure, the lower one passes beneath the anterior com- 

 missure, and the upper one passes over the anterior commissure and down in 

 front of it. 



