13G 



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

 the preceding and succeeding spines incline. In the Perameles the 

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

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

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

 flexibilit3' 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 totai number of 

 true vertebrse being thus the šame in all the genera. The an- 

 terior obliąue processes, ^hich begin to increase in length in the 

 three posteiior dorsal vertebrse, attain a great size in the lumbar 

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

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

 meles, and in the lašt lumbar vertebrse of all the other genera. The 

 transverse processes of the lumbar vertebrse progressively increase 

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

 veloped in the Wombat, •where they are directed obliąuely forwards. 

 In the Kangaroos, Potoroos, and Perameles they are curved for- 

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

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

 langers, and Opossums. 



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

 chylosed together in the sacral region of the sj^ine, amount in the 

 Wombat to seven ; but if ■^'e regard those vertebrse ouly as sacral 

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

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

 Cookii I have observed three sacral vertebrse, 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 vertebrse. 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 Alauge's Dasyure two sacral vertebrse are 

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

 anterior one that the innominata arejoined. The samekind of union 

 exists in the Viverrine Dasyure, but three vertebrse are anchylosed 

 together. In the Phalangers and Petaurists there are two sacral 

 vertebrse. In Petaurus taguanoides and Pet. macrurns three are 

 anchylosed together, though two only join the iliinn. In the ^Vom- 

 bat the transverse processes of the numeroiis anchylosed vertebrse 

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

 outwards and are confluent at their extremlties ; the remaining ones 

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

 tiiberosities of the isckia, behind which they gradually diminish in 

 size, and are lošt in the three lašt caudal vertebrse. The transition 

 from the sacral to the caudal vertebrse is very obscure in the Wom- 

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

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



