PROFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 



541 



as it ascends, to an obliquely truncate summit nearly 5 inches in fore-and-aft extent ; 

 narrow and ridgc-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 XLIII. 

 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 JElejphas 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 Biprotodon. 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 Biprotodon. 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, <? 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. 



