hel 
Petaurus breviceps, Phalangista vulpina, various species of 
Macropus and Potoroo, as well as a number of foetal specimens 
of these genera. 
GENERAL ACCOUNT OF THE CEREBRUM. 
The cerebrum of WVotoryctes presents an extreme simplicity of 
structure, and relatively a diminutive size fora Mammal. It is 
the lowliest Marsupial brain that I have examined, and compared 
with the size of its olfactory bulb, it is relatively smaller than 
that of any other Mammal with which I am acquainted. 
Although its ‘ pallial” development is far below that of both 
Monotremes, it exhibits features in its general plan of construc- 
tion which must be regarded as superior to the Prototherian con- 
dition. Thus it exhibits a greater degree of bending than either 
Monotreme.* It possesses a much more compact internal capsule 
than Ornithorhynchus, in spite of the smaller “ pallium.” 
Together with the olfactory bulb, each hemisphere has a 
roughly pyramidal form, with a base, which is almost vertical, 
directed backwards. Its superior surface presents a gradual 
incline backwards and upwards, whose slope may be readily ap- 
preciated from Dr. Stirling’s profile view of the skull (fig. 1, pl. 
vi.). The maximum length is about 13 mm., of which, roughly 
speaking, the anterior one-third is olfactory bulb and the posterior 
two-thirds cerebrum (figs. 1 e¢ 3). The maximum breadth of the 
hemisphere—near the posterior border—is 6°5 mm. ; and, as may 
be seen from the shape of the skull, and from fig. 2, it rapidly 
tapers as it is traced forwards, the somewhat heart-shaped 
olfactory bulb forming its apex. The posterior part of the 
olfactory bulb is slightly wider than the anterior extremity of 
the hemisphere, a fact which can be readily appreciated from the 
shape of the cranium in Dr. Stirling’s fig. 1, pl. vii. The 
maximum depth of the hemisphere is 10 mm. 
THE OLFACTORY BULB. 
The bulbus olfactorius is a large grey mass placed directly in 
front of, and not overlapped by, the hemisphere. It is lodged in 
a special compartment of the cranium, whose anterior and lateral 
walls, as well as the broad flat floor, are perforated by a large 
number of foramina. The cribiform floor of this ‘‘rhinencephalic” 
part (Owen) is separated from the rest of the cranial floor by a 
transverse bony ridge, which becomes more prominent as it is 
traced on to the lateral walls of the cranium. The continuation 
of this bony thickening in the roof forms the dark transverse line, 
already referred to, in fig. 1, plate viu., of Dr. Stirling’s paper. 
* See supplementary note, p. 193. 
