298 



incline. In the Bandicoots (Perameles) the centre of motion is at the eleventh dorsal 

 vertebra ; in the Potoroos and Kangaroos at the twelfth ; in the Petaurists at the thir- 

 teenth vertebra, In the Phalangers, Opossums, Koala, and "Wombat the flexibility of 

 the spine is much diminished, and the centre of motion is not defined by the conver- 

 gence of tin' spinous process towards a single vertebra, but they all incline slightly 

 backward. 



The lumbar vertebrae are four in number in the Phascolomys wmbatus, eight in the 

 Koala, seven in the Petaurists, and six in other Marsupialia — the total number of 

 kk true vertebra;" being thus the same (nineteen) in all the genera. 



The metapophyses, which begin to increase in length in the three posterior dorsal 

 vertebrse, attain a great size in the lumbar vertebrae, and are locked into the interspace 

 between the anapophyses and postzygapophyses, except in Perameles, and in the last 

 lumbar vertebra of all the other genera. The diapophyses of the lumbar vertebrae 

 progressively increase in length as the vertebra; approach the sacrum; they are most 

 developed in the Wombats, where they are directed obliquely forward. In the 

 Kangaroos, Potoroos, and Bandicoots they are curved forward and obliquely down- 

 ward. The length of these and of the anterior oblique processes is relatively least 

 in the Petaurists, Phalangers, and Opossums. 



The number of vertebrae succeeding the lumbar, which are anchylosed together in 

 the sacral region of the spine, may amount in some kinds of Wombat to seven ; but if 

 we regard those vertebrae only as 'sacral' which join the ossa innominata, then there 

 are but three. In the Kangaroos and Potoroos the impetus of the powerful hinder 

 extremities is transferred to two anchylosed vertebrae. In Perameles there is only a 

 single sacral vertebra, the spine of which is shorter and thicker than those of the 

 lumbar vertebra;, and turned in the contrary direction, viz. backward. In Myrmecobius 

 there are four sacral vertebrae by anchylosis, two of which join the ilia. In Mauge's 

 Dasyure two sacral vertebra; are anchylosed ; but it is to the expanded transverse pro- 

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

 union exists in the Viverrine Dasyure ; but three vertebrae are anchylosed together in 

 this species. In the Phalangers and Petaurists there are two sacral vertebrae. In 

 Petaurus taguanoides and Pet. macrurus three are anchylosed together, although two 

 only join the ilium. 



The transition from the sacral to the caudal vertebrae is obscure in the Wombats ; if 

 we limit the sacral to the three which join the ilium, then there remain twelve vertebrae 

 for the tail. The spinal canal is complete in all but the last three, which consist only 

 of the central element. There are no inferior spines; and as only the six posterior 

 vertebrae, which progressively diminish in length, extend beyond the posterior aperture 

 of the pelvis, the tail is scarcely visible in the living animal. In the Koala the tail is 

 also very short. In one species of Perameles I find eighteen caudal vertebrae, in another 

 twenty-three. In two species of Potoroo there are twenty-four caudal vertebrae ; but the 

 relative length of the tail differs in these by one third, in consequence of the different 



