1867.] DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. 80.5 



the four neural spines in advance of it are subequal in length, be- 

 sides being shorter. 



Dorsal vertebra:. — Among the Marsupialia the dorsal vertebrae 

 are thirteen in number, except in Phascolomys wombat, which has 

 fifteen. P. platyrhinus, then, agrees with the latter in this respect ; 

 but P. latifrons, on the other hand, disagrees with its two allied 

 specific forms, and reverts to the usual marsupial character. 



In the three species of Phascolomys the number of dorsal and 

 lumbar vertebrae taken collectively are nineteen. Of these, in P. pla- 

 tyrhinus and P. wombat, as the preceding formula shows, there are 

 fifteen dorsal and four lumbar ; but in P. latifrons there are only 

 thirteen rib-bearing dorsal, and consequently six lumbar vertebrae. 



The bodies of the dorsal vertebrae in P. platyrhinus and P. wom- 

 bat resemble each other, excepting in size. The under surfaces of the 

 centra are slightly laterally compressed, which gives the appearance 

 of increased vertical depth, which they otherwise do not possess ; 

 this is most marked in the large adult male of P. platyrhinus. 

 The bodies increase in antero-posterior thickness from the first to 

 the last. 



In the size of the bodies of the dorsal vertebrae P. latifrons agrees 

 most with P. wombat. One specimen of P. latifrons presented a 

 peculiar flattening of the under surface of the bodies. 



In the largest P. platyrhinus the laminar arches are flatter and 

 altogether broader. A better comparison is made between P. wombat 

 and P. latifrons, on account of the equality of size ; this brings out 

 the fact that in the latter the neural laminae, as seen from above, 

 are relatively narrower than in the former species. 



In one specimen of P. latifrons the neural spine of the first dorsal 

 possessed a bifid tip, in all the other specimens of this and the two 

 species compared it was single. In P. platyrhinus the same spine 

 at its upper half has considerable antero-posterior flattening. This 

 terminal flattening is just observable in P. wombat ; but in P. lati- 

 frons, excepting the divergence of the bifid extremity, the spine is 

 laterally compressed. 



The remainder of the neural spines are relatively longer and more 

 laterally compressed in the species P. latifrons ; their antero-posterior 

 diameter is also greatest. 



In the powerful body of P. platyrhinus the dorsal spinous pro- 

 cesses have each a bulbous extremity, and the sides of each spine are 

 marked by grooves for the attachment of muscles. 



All three species have the first dorsal spine the longest, those 

 behind diminishing gradually until they reach the shorter and broader 

 neurapophyses of the lumbar region. 



In the Common Wombat, as Owen has mentioned*, the metapo- 

 physis rises suddenly from the outside of the prozygapophysis of 

 the twelfth dorsal, increases in length to the second lumbar, dimi- 

 nishes by degrees to the second sacral, and is rudimental in the fol- 

 lowing sacral and caudal vertebrae. The same remarks apply to the 

 Platyrhine Wombat. 



* Osteological Catalogue Coll. Surg. vol. i. p. 330 (1853). 



