546 



PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 



the other side ; it may be a vertebra, as is sometimes seen in the Kangaroo and other 

 mammals, transitional between the dorsal and lumbar series, having the characters of a 

 rib-bearer on one side and not on the other. A trace of roughness on the side of the 

 fossil centrum corresponding to the protuberance on the other side, may indicate there 

 a ligamentous attachment of a rudiment of the last free rib. The present vertebra, 

 whether interpreted as the last dorsal or first lumbar, shows the small extent to which 

 those vertebrae gained in length as they receded in position. The antero-posterior dia- 

 meter at the under part of the centrum is 2 inches 5 lines, at the upper part 2 inches 

 10 lines; the breadth of the anterior surface is 4 inches 10 lines, the vertical diameter 

 of the same surface is 3 inches 9 lines. The epiphysial plate adheres to this surface ; it 

 is concentrically marked, thinning off to the centre, where it leaves a vacuity transversely 

 oblong, 1 inch 4 lines by 1 inch in its diameters. From the opposite surface the epi- 

 physis has been detached, showing the radiate disposition of the rugge of the diaphysial 

 surface, and the proportions contributed by the bases of the neurapophyses to the ver- 

 tebral body. 



In the next vertebral body, of similar dimensions, the anterior epiphysis is adherent, 

 but with the line of suture conspicuous ; it is from 3 to 4 lines thick at the periphery, 

 and thins off toward the centre, where it leaves a vacuity of about 1 inch in diameter. 

 The surface, for 1 inch at the periphery, is moderately convex, the rest is flat. The free 

 surface of the centrum is greatly and equably concave lengthwise. At the middle of the 

 neural surface is a transversely oblong venous fossa, 9 lines by 6 lines in diameters. This 

 centrum adheres by matrix to the succeeding one, which, repeating the characters above 

 noted, retains about 1 inch of the neurapophysial pedicles or lamellae. Each at its origin 

 has a fore-and-aft extent of 2 inches, contracting to 1 inch 8 lines at the fractured end ; it 

 rises nearer the fore than the hind end of the centrum. The extreme thickness (1 inch) 

 is toward the fore part of the pedicle. The transverse diameter of the neural canal at 

 the broken ends of the pedicles is 3 inches 6 lines. The venous fossa is repeated 

 in this as a single median one ; but in another lumbar centrum the entry is divided 

 by a median longitudinal tract of the neural surface, as is commonly the case in the 

 Kangaroo, 



In the third of these the left pedicle is preserved to a height of 2 inches, expanding 

 then to an antero-posterior extent of 2 inches 3 lines, and a transverse one of 1 inch 5 lines ; 

 at the lower contracted part of the neurapophysis these diameters are, respectively, 1 inch 

 9 lines and 1 inch. Yet the whole of the outer surface is smooth without trace of out- 

 standing transverse process ; whereas in both Kangaroo and Wombat that process comes 

 off at the junction of the neurapophysis with the centrum. We may therefore infer that 

 the neural arch of the lumbar scries was loftier in Biiirotodon, as we have already seen 

 it to have been in the two anterior dorsal vertebrae preserved. The epiphysis is wanting 

 from the hind surface of the third lumbar described, and the sutures of the neurapophyses 

 with the centrum are there exposed. They project a little beyond the epiphysial surface 

 of the centrum. The largest and hindmost of the present series of lumbars (Plate XLIV. 



