179 
Extending forwards and outwards into each of these fosse there 
is a fissure—the sphenoidal—which, with its fellow of the oppo- 
site side, forms a blunt V-shaped slit, which limits the spheno- 
ethmoidal eminence posteriorly. The foramen ovale is external 
to the carotid foramen. Immediately external to the former the 
alisphenoid is raised into a large thin-walled eminence, which 
extends forwards as far as the fossa for the tuberculum olfact- 
orium. Thisis the roof of the tympanic bulla and corresponds on 
the brain to the deep depression behind the tuberculum and 
slightly internal to the pyriform lobe. In Perameles the corre- 
sponding structure only extends forwards as far as the level of 
the foramen ovale. This bulla in Wotoryctes forms a large well- 
marked eminence of elliptical outline, whose posterior extremity 
touches the tip of the petrous temporal, which is directed for- 
wards. In this way a deep fossa is formed for the natiform 
eminence on the outer side of the bulla. The greater part of this 
fossa is formed by the alisphenoid, but it is bounded also in part 
by the petrous and squamous temporals. The opening of the 
large floccular fossa on the dorsal aspect of the petrous periotic 
is directed inwards and forwards. The attachment of the ten- 
torium cerebelli to the basisphenoid helps to deepen the trough in 
which the large trigeminal nerve lies, and separates it from the 
pituitary. 
The resemblance between the base of the brains of Wotoryctes 
and Perameles is much more striking than is that of the baszs 
cranu. The brain is modified directly in relation to certain 
functional demands, whereas the basis cranii is moulded to 
accommodate the altered brain, without modifying its essential 
morphology. 
MesiaL ASPECT. 
In the greater part of its extent the mesial surface of the 
cerebrum is flat, and separated from the corresponding part of 
the other hemisphere by the falx cerebri. Posteriorly and in- 
feriorly, however, it is deeply hollowed out, or rather, pushed 
outwards by the thalam- and mes-encephalon, the upper part of 
the posterior extremity of the hemisphere forming a kind of cap 
for these structures. At the anterior and lower part there is a 
large pale area (fig. 3 p.a.), which is situated immediately behind 
the olfactory bulb. Elsewhere (36) I have proposed the name 
precommissural area for this region. Inferiorly it is directly 
continuous with the tuberculum olfactorium (¢.0.), from which it 
differs in being of a lighter color. Dorsally it is continuous with 
the anterior extremity of the fascia dentata (fd.), while 
posteriorly it is directly continuous with the thickened lamina 
terminalis (s.), which is the homologue of the septum lucidum of 
EKutheria. It resembles the latter structure very closely histo- 
