PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
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as it ascends, to an obliquely truncate summit nearly 5 inches in fore-and-aft extent ; 
narrow and ridge-like at the mid part, expanding and obtuse at the fore and hind angles, 
the latter being the thickest ; from each side of this angle a low ridge (Plate XLXII. 
fig. 1, g ) descends obliquely forward, subsiding upon the lateral surface of the spine. 
The neural canal is 2 inches 3 lines in width, and rather less in height, especially behind, 
where the vertical diameter is 1 inch 6 lines. A wide groove leads outward and down- 
ward from the canal between the postzygapophyses and the back part of the centrum. 
The upper (neural) surface of the centrum is impressed at its middle with a deep pit, to 
which a groove leads on each side ; the smooth surface has been broken away before 
and behind the pit, indicative of its having been crossed lengthwise by a bony bar, which 
would have converted the lateral groove into a pair of foramina. 
Of the quadrupeds resembling in size the Diprotodon . the Proboscidians have the axis 
most like that of the Australian giant, but the following differences present themselves. 
In Eleplias the odontoid is absolutely, as well as relatively shorter ; the anterior arti- 
cular surfaces are less uniformly convex and less convex in any direction ; the neural 
spine is relatively lower, much thicker transversely, with a subquadrate termination or 
upper surface, canaliculate along the mid line, and deepening to produce a posterior 
bifurcation. The centrum has no hypapophysis. In Macropus , on the other hand, we 
find the hypapophysis is repeated both as to size and position ; the odontoid process also 
offers a like development, with resemblance in such details as the disposition and propor- 
tions of the pair of upper terminal surfaces for ligamentous attachment, and the poste- 
rior smooth surface for the transverse ligament. The neural spine is, however, more 
produced anteriorly and less so behind. 
In my ‘ Osteology of Marsupialia,’ I noted, as a result of observations on the skeleton 
of Macropus major , that “in the Kangaroo both the dentata and atlas have the trans- 
verse processes grooved merely by the vertebral artery”*. I have since observed in 
Macropus laniger the circumscription of the groove by the development of a slender 
parapophysis, as in Diprotodon. A similar vertebrarterial canal occurs in Phascolomys 
and Phascolarctos. The neural spine of the axis in the Wombat resembles in shape 
that in the Diprotodon , but is rather more produced behind. The hypapophysis is, how- 
ever, a mere medial low ridge ; that in the Kangaroo is significantly more like the pro- 
cess in Diprotodon. In both Macropus , Phascolomys , and Phascolarctos a pair of con- 
spicuous foramina near the hind part of the upper (neural) surface of the centrum lead 
to canals converging as they sink in the osseous substance to a common (venous) passage ; 
these are not present in Proboscidians ; a few minute irregular venous foramina may be 
seen on the corresponding surface of the axis vertebra. 
The third (Plate XLIV. fig. 4) and two consecutive (Cut. fig. 5, c 3, c 4) cervical ver- 
tebrae resemble by their shortness those of the Wombat rather than of the Kangaroo; 
they are by no means, however, so compressed from before backward as in the Probo- 
scidians. 
* Trans. Zool. Soc. vol. ii. p. 394; see also Art. Marsupialia , Cycl. of Anat. p. 276. 
