VIRGINIAN OPOSSUM. 
4G7 
meeting so as to form a much-elevated sagittal crest; the 
interorbital space is moderately broad, hut in the temporal 
region the skull is much contracted : an obtuse post-orbital 
process is thrown out from the frontal hone, and the malar 
bone is also produced into an angular process, so as partially 
to separate the temporal from the orbital fossa. The zygo¬ 
matic arch is curved both outwards and upwards. The nasal 
bones arc broad towards the hinder part, and are produced 
posteriorly so as to encroach much upon the frontal hones. 
This is one of the points of distinction which strikes one 
upon comparing the skulls of the Opossum with that of a 
Dasyurus, the nasal hones in the animals of that genus being 
much less produced in the mesial line of the skull; their 
greatest diameter is at the hinder part, whilst in the Opossum 
the broadest part of the nasal hones is always considerably 
in advance of that point. Another distinction observable 
in these bones, when the Dasyurida and Didelphidce are 
compared, consists in their being pointed in front and pro¬ 
duced considerably over the entrance of the nasal cavity in 
the latter group, whilst in the Dasyures the nasal bones are 
truncated or emarginated in front, so that the upper boundary 
of the nasal cavity terminates in a line with the lateral 
boundaries formed by the intermaxillaries, or behind that 
line. The facial portion of the skull is larger, the cerebral 
portion smaller in proportion than in the Dasyuri and the 
palate is longer. 
1 The brain, as in a great measure indicated by the structure of the skull, 
is remarkable for the proportionately large size of the olfactory lobes, and the 
small size of the cerebral hemispheres; these latter are much contracted in 
front, and destitute of convolutions. As compared with the brain of the 
Mammalia of the higher classes, that of the Opossum furnishes the most 
remarkable contrast in its small size in proportion to the bulk of the animal, 
and the small development of the cerebrum, which is here distinctly separated 
from the cerebellum, and leaves exposed the optic lobes above, as well as the 
crura cerebri below. The Dasyuri come next in grade, and their brain con- 
