172 
The mesial surfaces of the olfactory bulbs (fig. 3, olf. 6.) are flat 
and separated from one another merely by the falx cerebri. There 
does not appear to be any depression upon the mesial aspect of 
the olfactory bulb such as is found in Perameles, and which has 
been distinguished in Didelphis as the “‘ mesal olfactory fossa” by 
Herrick (17). The inferior surface of the bulb is flat and rough 
from the insertion of olfactory nerves. Posteriorly it is separated 
‘from the base of the brain by a deep curved sulcus (fig. 2). The 
lateral aspect is rough and convex, in accordance with the shape 
of the cranium, and is separated from the cerebrum proper by a 
well-marked furrow, in which the external olfactory radiation 
(tig. 1, e.o.r.) appears to arise. 
On ali aspects, therefore, the olfactory bulb is separated from 
the hemisphere proper by a deep constriction, in the depths of 
which the prosencephalic part of the bulb is continuous with the 
hemisphere. This constricted neck of tissue will be distinguished 
as the olfactory peduncle. 
The olfactory bulbs stained remarkably well with anilin blue 
black, and their structure was clearly demonstrated. There is a 
large olfactory ventricle continuous posteriorly (as in all Mono- 
tremes and Marsupials and most lowly Mammals) with the 
anterior horn of the lateral ventricle. The wall of the ventricle 
is arranged (fig. 11) in four well-marked zones—(1) a thick peri- 
pheral zone of non-medullated olfactory nerve fibres and glomeruli, 
(2) a clear zone containing numerous mitral cells, (3) a layer 
containing numerous radiating and concentric nerve fibres, and 
(4) a layer containing a dense mass of medullated nerve fibres, 
directly continuous externally with the external olfactory root, 
and internally with the internal olfactory root. The olfactory 
peduncle extends into the olfactory lobe immediately surrounding 
the ventricle, and forms a large mass on the other side of the 
olfactory ventricle, lying internal to the fourth layer described 
above. In the substance of this part of the peduncle the large 
pars olfactoria of the anterior commissure extends forwards (fig. 
11, p.o.). Its fibres enter the fourth layer described above, and 
cannot be further traced, as they are so intimately mixed with 
the fibres of the olfactory radiations. There is nothing else of 
note to describe in the histology of this region in Wotoryctes, as 
it agrees in all points with the fuller description given elsewhere 
(37). 
THE CEREBRUM PROPER. 
In describing the cerebral hemisphere, it will be convenient to 
consider it under three headings—(1) the cranial or lateral, (2) 
the basal or ventral, and (3) the mesial aspect. 
