PEOFESSOK OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 



545 



anchylosed lumbar vertebra of the Mylodon ; but the bodies of the dorsal vertebrae in 

 the great extinct Bmta are longer and narrower in proportion to their breadth than in 

 the present fossil. In the Kangaroo the upper surface of the body of the dorsal and 

 lumbar vertebra) is perforated by two vascular canals, which pass down vertically and 

 open below by a single or double outlet. In the Wombat the middle of the upper surface 

 of the bodies of the dorsal and lumbar vertebrse exhibits a single large and deep depres- 

 sion, which in the dorsal vertebrse has no inferior outlet, and in this character they closely 

 resemble the present fossil. The dorsal vertebrse of the Wombat are, however, longer in 

 proportion to their breadth. 



Thus the present mutilated vertebra alone would support the conclusion that there 

 had formerly existed in Australia a mammiferous quadruped, superior to the Ehinoceros 

 in bulk, and distinct from any known species of corresponding size. It is interesting 

 and instructive to find one well-marked character in it, viz. the median excavation on 

 the upper part of the body, repeated in the same vertebrae of one of the largest of the 

 existing Marsupialia. 



The remaining evidences of vertebrse in the Boydian or purchased series of Diprotodont 

 Fossils in the British Museum consist of five centrums and two pairs of detached ter- 

 minal epiphyses of those elements. 



The centrums, in the absence of any costal or hsemapophysial depression, in their 

 increased length and greater expanse of the neural canal, are referable to the lumbar 

 series. Three retain the coalesced bases of the neurapophyses, yet these do not develope 

 diapophyses in the extent to which they are preserved. 



The foremost of these lumbar centrums shows a length of 2 inches 4 lines at its lower 

 part, increasing to 2 inches 8 lines at its upper part ; the others, with slight general gain 

 of size, show the same proportions. Thus the one which seems the last of the series has 

 a length of 3 inches 3 lines at the lower part, and of 3 inches 8 lines at the upper part 

 of the centrum. Thus we may infer that the part of the spine from which these vertebras 

 have come was habitually bent in Bij^rotodon w^ith the concavity downward. The degree 

 of increased length in the last over the longest of the other three centrums indicates two 

 or three missing vertebrae intervening between those to hand. The Kangaroo has six 

 lumbar vertebrae, the Koala eight, the Wombats only four {Phascolomys vomhatus) or 

 five {Phascolomys latifrons). Six lumbars is the rule in Marsupialia, and I incline to 

 view Biprotodon as amenable thereto, rather than as repeating the exceptional formula 

 of Phascolomys* . 



In the foremost of the five fossil lumbar centrums a small protuberance from the upper 

 and fore part of one side indicates the rudiment of a diapophysis ; it is not present on 



* As I was led to note in my ' Osteology of Marsupialia,' he. cit., p. 396, the number of free trunk-vertebrae 

 is signifieautly constant in that order, whatever be the difference of costal formiila ; thus, Pliascolarctos has 11 

 costal, 8 lumbar, =19 ; Petaurus, 12 costal, 7 lumbar, =19; Macropus, Phalangisia, Perameles, MyrmecoUus, 

 Phascogale, Didelphys, Dasyurus, Sarcophilus, Thyladnus, have severally 13 costal, 7 lumbar, =19 ; Phasco- 

 lomys vomhatus has 15 costal, 4 lumbar =19. 



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