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dorsal vertebra, by the verticality of its spine, towards which both 

 the preceding and succeeding spines incline. In the Peraraeles the 

 centre of motion is at the eleventh dorsal vertebra ; in the Potoroa 

 and Kangaroo at the twelfth ; in the Petaurists at the thirteenth 

 vertebra. In the Phalangers, Opossum, Koala, and Wombat, the 

 flexibility' of the spine is much diminished, and the centre of motion 

 is not defined by the convergence of the spinous process towards a 

 single vertebra, but they all incline slightly backwards. 



" The lumbar vertebrae are four in number in the Wombat, seven 

 in the Petaurists, and six in other Marsupiata, the total number of 

 true vertebrae being thus the same in all the genera. The an- 

 terior oblique processes, which begin to increase in length in the 

 three posterior dorsal vertebrae, attain a great size in the lumbar 

 vertebrae, and are locked into the interspace of the posterior ob- 

 lique processes, which are double on each side, except in the Pera- 

 meles, and in the last lumbar vertebrae of all the other genera. The 

 transverse processes of the lumbar vertebrae progressively increase 

 in length as the vertebrae approach the sacrum ; they are most de- 

 veloped in the Wombat, where they are directed obliquely forwards. 

 In the Kangaroos, Potoroos, and Perameles thej^ are curved for- 

 wards, and obliquely downwards. The length of these and of the 

 anterior oblique processes is relatively least in the Petaurists, Pha- 

 langers, and Opossums. 



" The number of vertebrae succeeding the lumbar, which are an- 

 chylosed together in the sacral region of the spine, amount in the 

 Wombat to seven ; but if we regard those vertebra? only as sacral 

 which join the innominata, then there are three. In the Pha- 

 langers there are generally two sacral vertebrae ; but in a Phal. 

 Cookii I have observed three sacral vertebra;, both by anchylosis 

 and juncture with the ossa innominata. In the Kangaroos and 

 Potoroos the impetus of the powerful hinder extremities is trans- 

 ferred to two anchylosed vertebrae. In the Perameles there is 

 only a single sacral vertebra, the spine of which is shorter and 

 thicker than those of the lumbar, and turned in the contrary direc- 

 tion, viz. backwards. In Mange's Dasyure two sacral vertebrae are 

 anchylosed, but it is to the expanded transverse processes of the 

 anterior one that the innominata are joined. The same kind of union 

 exists in the Viverrine Dasyure, but three vertebrae are anchylosed 

 together. In the Phalangers and Petaurists there are two sacral 

 vertebrae. In Petaunts taguanoides and Pet. macrurus three arc 

 anchylosed together, though two only join the ilium. In the Wom- 

 bat the transverse processes of the numerous anchylosed vertebrae 

 are remarkable for their length ; those of the first four are directed 

 outwards and are confluent at their extremities ; the remaining ones 

 are turned in a slight degree backwards, and very nearly reach the 

 tuberosities of the ischia, behind which they gradually diminish in 

 size, and are lost in the three last caudal vertebrae. The transition 

 firom the sacral to the caudal vertebra; is very obscure in the Wom- 

 bat ; if we limit the sacral to the three which join the ilium, then 

 there remain twelve vertebrae for the tail. The spinal canal is com- 



