Lirare 
development (such as Dasyurus, Petaurus, Phalangista) the 
rhinal fissure, and therefore part of the “ pallium” would be seen 
in a basal view of the brain. In Platypus, with its small pyri- 
form and large pallium, the rhinal fissure is quite near the middle 
line of the base. 
The huge size of the tuberculum olfactorium gives quite a 
characteristic appearance to the base of the brains of Votoryctes 
and Perameles. Ganser says (13) that in the mole this part of 
the brain, which he calls “ Rinde am Kopf des Streifenhiigels,” is 
larger than in any other animal with whose cerebrum he is 
acquainted. In Perameles, however, it is much bigger, and more 
prominent than it would seem to be in Z'alpa (Ganser), Dasypus 
(Turner), Lrinaceus, or Chlamydophorus (Hyrtl), all highly 
macrosmatic animals. In WNotoryctes it reaches a still higher 
development, forming a hemispherical mass, which is almost as 
large as the eminentia natiformis. In the macrosmatic Hypsi- 
prymnus and Dasyurus, although it is large and prominent, it 
appears small and flat when compared with the same region in 
Notoryctes. In Phalangista and Petaurus it is almost quite flat, 
corresponding to the lesser development of the olfactory organ. 
In such it can readily be homologised with Broca’s (5) espace 
quadrilatére or middle (grey) olfactory root. In Macropus and 
Petrogale, although it is large, it is not prominent, owing to the 
large size of the rest of the brain. In Ornithorhynchus it forms 
a small elliptical swelling. In TZalpa, and apparently also in 
Chlamydophorus, according to Hyrtl’s notes, it would appear to 
be little, if anything, larger than in Dasyurus. This will give 
some idea as to its immense size in Notoryctes. Superficially it 
is covered by a medullary coat from the external olfactory radia- 
tion. In addition to the names already applied to this mass 
above, it has been distinguished in Didelphis and Sauropsida as 
the ‘‘post-rhinal lobe” by Herrick (17). It corresponds to the 
“orbital lobe” of Turner in Dasypus sexcinctus (41), and possibly 
to Burckhardt’s “ lobus post-olfactorius” in Protopterus annectans. 
In man its homologue is probably found in the atrophic grey 
matter found in the locus perforatus anticus of Vicq d’Azyr.* It 
is intimately connected with the olfactory bulb, and varies in 
size with that organ. It is therefore ridiculous to exclude it 
from the rhinencephalon as Hill has done (19) in the case of 
Ornithorhinchus. 
This peculiar development of the base of the brain has a 
*In all Marsupials and Monotremes there is a small flat area behind 
the tuberculum olfactorium, which corresponds to what Burt Wilder calls 
the ‘‘ portio depressa” in the cat. This is the true homologue of the 
locus perforatus. In man, where the tuberculum atrophies and no longer 
forms a prominence, the term is vaguely used for the whole region. 
