181 
When the hippocampus bends down posteriorly with the hemi- 
sphere, as it does in Marsupials, the hippocampal commissure 
takes a corresponding bend (35), so that it limits the thickened 
lamina terminalis behind and below as well. This thickened 
lamina terminalis represents the septum pellucidum of Eutheria, 
and corresponds to the appearance seen, according to Marchand 
(23) and Paul Martin (24), in the development of the commissures 
of higher Mammals. It corresponds to part of Rabl-Rickhard’s 
(31) “Ammonswulst,” which lies external to, rather than below, 
the hippocampal commissure in Reptiles. In the evolution of the 
septum lucidum a gradual progression may be seen from Reptiles 
to Platypus, from the latter to the Marsupial condition, and from 
the latter to the lowly Eutheria such as Frinaceus or the 
Edentata.. 
The large rounded section of the anterior commissure will be 
seen in the lower part of the lamina terminalis, and in the upper 
part the large V-shaped sagittal section of the hippocampal or 
fornix-commissure. The relative size of these two commissures 
is about the same as in Perameles. The hippocampal commissure 
of course varies directly in size with the hippocampus. The 
anterior commissure, however, is a compound bundle, composed 
of a rhinencephalic and a pallial part, each of which varies with 
the size of its area of “‘ Ursprungzellen.” In Eutheria, however, 
a considerable part of the pallium is connected by the corpus 
callosum. Hence in them the size of the anterior commissure 
will depend largely (but not wholly) upon the size of the olfact- 
ory bulb (of course the pyriform and tuberculum increase pro- 
portionately to the bulb). Thus among the Edentata with their 
small pallium and large rhinencephalon (Turner, 41, Rabl- 
Ruckhard, 30) and in Hrinaceus (Flower, 11), the anterior com- 
missure is very large. In all Marsupials and Monotremes it is 
large, because it takes the place of the corpus callosum, and con- 
nects the whole of the pallium, so that it is very large in the 
higher members like Hchidna, Macropus, and Thylacinus, which 
have large pallia. 
In Notoryctes (as in all Marsupials) the hippocampal commis- 
sure is bilaminar (fig. 10), consisting of a dorsal (ps.d.) and a 
ventral limb (ps.v.), connected posteriorly by a “ spleniwm” (spl.). 
These two parts do not, however, correspond to the psalterium 
dorsale et ventrale of Honegger (21) in placental Mammals, since 
the ventral limb (ps.v.) of the Marsupial hippocampal commissure 
is the representative of the whole psalterium of Eutheria (35). In 
addition to the hippocampi, the hippocampal commissure also 
connects the precommissural aree. This part corresponds to the 
“corpus callosum” of Herrick and the “commissura pallii 
antertor” of Rabl-Rickhard (31). Arguing from the arrange- 
