266 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA, 
The floor of the orbit presents an oblong depression (the “ entorbital fossa”), with 
a sharp anterior and superior margin. From the fore part of this depression proceeds 
the suborbital canal, commencing by a large circular hole (“ entorbital foramen ”) ; a little 
way behind this is a smaller (“ spheno-palatine ”) foramen. 
The inner wall of the orbit, formed by the maxillary and palatine, curves outward 
and upward from the upper border of the depression to unite with that in advance con- 
tributed by the lacrymal, leaving the outer circumference of the entorbital foramen free 
from any direct rise of the interorbital plate. Anterior to the entorbital canal there 
is a more shallow and imperforate depression affecting the lower part of the lacrymal, 
at a little distance from the anterior border of the orbit. This structure of the orbital 
surface agrees with that in Macropus and Osphranter , with minor differences. 
In Macropus major the entorbital fossa is deeper, the sharp upper border being 
extended backward beyond the spheno-palatine foramen ; there is a third smaller 
“ ptery go-palatine ” foramen at the end of that border ; but the fractured state of the 
fossil prevents the determination of its agreement or otherwise in regard to that third 
foramen. 
In Osphranter rohustus the second foramen is as large as the first, and is situated to 
its inner side and very little posterior to it, the intervening bony plate with a sharp 
concave edge forming the inner border of the entorbital foramen and the antero* 
external border of the more oblique spheno-palatine foramen. 
In Sthenurus Atlas the upper border of the entorbital fossa, in its shortness and 
degree of sharpness, is more like that in Macropus Titan. The inner wall of the orbit 
ascends rather more directly therefrom than in Macropus major. The pterygo-palatine 
foramen in the palatine part of the inner orbital wall is more minute in Osphranter 
than in Macropus . In Phascolagus erubescens the proximity of the first and second 
foramina is closer than in Osphranter. 
In the unique skull of Boriogale magnus it appears that part of the inner wall of the 
orbit completing, above, the circumference of the second foramen is unossified ; and 
such part of the skull in a petrified state would show only one large circular orifice, 
answering to the first or entorbital one in Macropus major and Macropus Titan. In 
the comparison of the orbital part of the skull, Macropus Titan^ in the relative size and 
position of the two anterior foramina (entorbital and spheno-palatine), agrees with 
Macropus major more closely than with the above-cited representatives of other sub- 
genera of living Kangaroos. 
From the upper and anterior margin of the entorbital foramen (Plate XXIV. fig. 5, o) 
rises a plate of bone ( n , figs. 4 & 5), quickly narrowing to form part of the inner wall of 
the orbit, or partition-wall between that cavity and the nasal one. This structure implies a 
less relative depth, or diameter, of the orbit from without inward or transversely than in 
the existing genera above cited *. But a nearer approach to the above-defined orbital 
* Whence may be inferred a smaller eyeball, associated perhaps with more diurnal habits, than in the still 
living Kangaroos. 
