THE FOREBRAIN OF THE ALLIGATOR 337 
free zone and, in the turtle, by the sulcus limitans hippocampi. 
Farther caudad, however, the line of separation between the two 
becomes indistinct. In the region just anterior to-the commis- 
sure, if the writer has understood Johnston correctly, the sulcus 
disappears. Certainly in both the alligator and the turtle (Cis- 
tudo carolina) the cell-free zone disappears and there is no line 
of demarcation, so far as could be determined from the material 
available, between the primordium hippocampi and the more 
posterior portion of the nucleus parolfactorius lateralis. A cell 
mass is thus formed which has cells apparently of the type both 
of the primordium hippocampi and of the lateral parolfactory 
nucleus, although the latter type appears to predominate. Con- 
sequently, Herrick (10) after a study of amphibian and reptil- 
ian material (including Lacerta, Cistudo carolina, and Alligator 
mississippiensis) and after an examination of embryonic reptilian 
brains from the Harvard collection, reached the conclusion that 
this nucleus was a part of his septal nucleus, consisting of cells 
of the basal region which had invaded this region, migrating 
upward along the descending hippocampal fibers. 
Johnston (713), on the other hand, has considered this inter- 
mediate cell group a part of the primordium hippocampi, basing 
his conclusion partly on the presence of the fornix fibers and the 
fibers of the hippocampal commissure, and especially on its 
position, as he believes from a study of embryonic material, 
above the neuroporic recess in a thickened portion of the lamina 
supra-neuroporica. 
In the more anterior part of the brain, the ventro-lateral, small 
celled area (Johnston’s caudate nucleus) is apparently continued 
around the corner of the ventricle to the medial surface (figs. 
7 to 9, 16, 17). This continuation of the caudate has been 
termed nucleus accumbens by many observers. Johnston in- 
cludes this nucleus accumbens in his nucleus parolfactorius 
lateralis. 
It will be seen from the above discussion that the terms lat- 
eral septal nucleus (Herrick 710) and lateral parolfactory nu- 
cleus (Johnston *13 and 715) are not synonymous. If the writer 
has understood the authors correctly, the two masses compare 
