522 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
The basioccipital, as it advances, expands and gains a thickness of nearly an inch of 
compact and minutely cellular bony tissue. 
The occipital condyles (Plate XXXV. fig. 3, 2 ), an inch apart below and 2^ inches apart 
above, have their lower extremity obtuse, about an inch broad, curved inward and forward ; 
they expand as they ascend, diverging to a breadth of 2 inches at their upper ends. The 
vertical convexity of each condyle describes a semicircle, the extent of the articular 
surface following this curve being 6 inches. The outer border is longer than the inner 
one, so that the upper margin of the condyle rises obliquely from within outward. The 
narrow lower ends of the condyles rise or project more abruptly from the intervening 
basioccipital border of the foramen magnum than in Macropus. Each condyle is here 
impressed by a rough surface or shallow notch at its inner surface, indicative of tendinal 
insertion. A low narrow ridge extends from the outer part of the lower end of the 
condyle, forward, and may indicate the lateral extent of the basioccipital at this part. 
The transverse convexity of the condyle is greater, less angular, especially at the lower 
half, than in Macropus. The oblique base or upper end of the condyle projects pro- 
portionally more from the non-articular part of the exoccipital. A similar better defi- 
nition or greater prominence characterizes the outer margin of the condyle ; the inner 
margin forming the sides of the foramen magnum is sharper and better defined than in 
Macropus : these borders are also less divergent as they rise. The inner, non-articular 
side of the condyle is slightly concave, rough, subtuberculate. The outer border of the 
articular part is sharp, and projects over the inner non-articular side of the condyle. In 
their posterior terminal position and degree of prominence the occipital condyles of 
Diprotodon resemble those in Dinotherium. 
The foramen magnum (ib. fig. 3, 0 ) is bounded above by the arched obtuse border of 
the exoccipitals, which bones rapidly gain thickness as they extend from the foramen. , 
I assume that the exoccipitals met above the foramen, as in many Marsupials ; or, if not 
meeting, had their interspace filled by the superoccipital, as in Phascolarctos : they left 
here no notch, such as one sees in Macropus Bennettii. The upper border of the 
foramen magnum is non-emarginate in Macropus major ; but it is relatively of greater 
extent in that Kangaroo, through the greater divergence of the condyles, and it is less 
arched or concave transversely than in Diprotodon. Two precondyloid foramina open 
upon each exoccipital, opposite the junction of the lower and middle thirds of the 
condyle, from which the hindmost foramen is distant 9 lines, the next 1 inch 2 lines ; 
each foramen is about 4 lines in diameter. An irregular or tubercular ridge curves over 
the fossa of the precondyloid foramina, expanding to be lost on the paroccipital. This 
process (ib. figs. 1 & 3, 4 ) is tuberous, thick, and short ; it is not so much produced as 
in Macropus. 
The foramen magnum is more erase than in Macropus , i. e. it expands funnel-wise to 
its outlet, backward, and especially above and below ; it has more the character of a 
short (neural) canal than a foramen, through the antero-posterior extent of its wall or 
rim. It is transversely elliptical, 2 inches 5 lines in long, 1 inch 3 lines in short, dia- 
