544 



PEOrESSOE OWEN ON THE EOSSIL MAMMALS OF AUSTEALIA. 



the upper part on each side the small intervening proportion of the centrum proper 

 (ib. fig. 8, c). Posteriorly they also slightly project (fig. 7, n) beyond the flat surface of 

 the centrum (ib. c) ; and a smooth tract of the neural canal (fig. 8, n', n') is continued 

 backward upon each of these prominences. The fore surface of the centrum is in a 

 very slight degree convex ; both surfaces are epiphysial or rough, with the usual tendency 

 to a radiate disposition of the fine furrows. The postzygapophyses (z') are somewhat 

 more prominent than in the former dorsal (figs. 5 & 6), and the neural spine slopes a 

 little backward. This process is narrower transversely than in fig. 5, and is longer prior 

 to its bifurcation (fig. 8, ns). Its strengthening ridges, especially the anterior one, are 

 more developed ; the bifurcation of the summit is repeated in this as in the foregoing 

 vertebra, with slight divergence of the terminal prongs, both of which have lost their 

 summits. 



In the whole range of the Mammalian series I know of no dorsal vertebrae with cha- 

 racters like the subjects of figures 5-8. Where vertebrae are notable for their shortness 

 and lamelliform type they are confined to the region of the neck, as, e. g., in Prohoscidia 

 and Cetacea ; but the dorsal series, in these, promptly resumes the ordinary proportions 

 of length of centrum. Similarly, where the transversely bifurcate character of the 

 neural spine is met with {e. g. Elephant, Man), it is restricted to one or two of the cer- 

 vical series ; in Diprotodon only is it known to exist in a dorsal vertebra. What modifi- 

 cation may ensue or at what distance from the neck in other or posterior dorsal vertebrae 

 my present materials do not enable me to state. I infer that the more usual proportions 

 are acquired in the posterior dorsals from the slight increase presented in the following 

 specimen, and from those which certain of the lumbar vertebrae present. 



The specimen referred to, which forms part of the collection in the Museum of the Royal 

 College of Surgeons, consists of the centrum only. 



It measures 2 inches 3 lines in antero-posterior diameter, 3 inches in vertical diameter, 

 and 4 inches 9 lines in transverse diameter. Both articular extremities are flat ; the epi- 

 physial plates are anchylosed ; but where they are broken away the radiating rough lines, 

 characteristic of the epiphysial surface, indicate that the union was tardy and had been 

 recently effected before the animal perished. This vertebra diff"ers by its compressed 

 form and the flattening of the articular ends from the dorsal vertebrae of the ordinary 

 placental Pachyderms, but resembles in these characters the dorsal vertebrae of the Pro- 

 boscidians ; in these, however, the breadth of the vertebral body is not so great as in the 

 fossil. From the cetacean vertebrae the present fossil is distinguished by the large 

 concave articular surface at the upper and anterior part of the side of the body for the 

 reception of part of the head of a rib ; this costal surface, which is not quite entire, 

 appears to have been about 1^ inch in diameter. The neurapophyses are anchylosed to 

 the centrum, but the internal margins of their expanded bases are definable, and have 

 been separated by a tract rather less than 1 inch in breadth, of the upper surface of the 

 centrum ; at the middle of this surface there is a deep transversely oblong depression. 

 A similar depression is present in some dorsal vertebra3 of the 3Iegatherium and in the 



