486 PEOFESSOE OWEN ON THE SPECIES OP PHASCOLOMTS. 



The number of vertebrae which are confluent in the sacral region of Phascoloniys 

 latifrons is four (PI. LXX. fig. 1, s i-s 4), the two foremost of which articulate with 

 the ilia. The syndesmotic surface is formed on each side by an expansion of the hinder 

 half of the diapophysis of the first vertebra (ib. d \) and of the whole of that of the 

 second [d 2), forming together an oblong subreniform tract (ib. fig. 2) with an indication 

 of its division into two surfaces {d 1, d 2). The entire longitudinal extent of this joint is 

 1 inch 2 liues, with an extreme breadth of 6 lines. The diapophyses are confluent along 

 their expanded distal halves of the fii'st and second, and by a less proportion in the third 

 and fourth sacrals, leaving vacuities {sd i-sd 3) between their proximal portions, into 

 which open the joints between the bodies of the sacral vertebrae. These joints are not 

 anchylosed in the specimen figui-ed. The bodies of the sacral vertebrae (ib. fig. 1, s i-s 4) 

 are depressed, losing vertical extent as they recede, but maintaining breadth beyond the 

 first, which is the largest. In the first sacral the prezygapophyses resemble those of 

 the lumbar vertebrae, and develop external to the joint a small tuberous metapophysis. 

 The postzygapophyses are small; and both articular processes of the neural arch 

 decrease in size to the last sacral. Between this and the third sacral the coalescence 

 is limited to the extreme ends of the diapophyses, which in the last (d 4) are produced 

 forward. 



In the first caudal (ib. fig. 1, c 1) the broad depressed diapophyses (d 5) are cuned 

 backward, as in the succeeding caudals (d 6, d 7). 



In a large full-grown Phascoloniys platyrhinus there are four sacral vertebrae by ter- 

 minal coalescence of diapophyses, the two anterior of which articulate with the ilia, the 

 articular surface being extended along the whole terminal expanse of the first sacral 

 diapophyses. The fifth vertebra by the backward direction of its diapophysial expan- 

 sions indicates its caudal characters ; but on the right side the diapophysis is confluent 

 with that of the following vertebra. 



In the sacrum of a second, not quite full-gro\vn, example of Phascolomys platyrhinus 

 (PI. LXX. fig. 3) the vertebra (c 1) succeeding the four anchylosed sacrals has its dia- 

 pophyses {d 5) similarly directed and expanded, the left touching the one in advance by 

 its extreme angle, with the interposed ligamentous matter not yet ossified. In the 

 sixth vertebra (c 2) the diapophysial expansions extend backward and coalesce at their 

 hinder angles with the diapophyses of the seventh vertebra, forming, as it were, a second 

 smaU sacrum {d 6, d 7), according to the character of coalescence. 



The articular surface for the ilium (PL LXX. fig. 4) is longitudinally more extended, 

 and the proportions contributed by the first and second sacrals {d i, d^) are further 

 apart than in Phascolomys latifrons (fig. 2). 



In the example oi Phascolomys vombafus, described in the ' Catalogue of the Osteology 

 in the Museum of the Eoyal College of Surgeons' (4to, 1853, no. 1814, p. 383), anchy- 

 losis of the fifth vertebra having expanded antroverted diapophyses with those of the 

 fourth sacral has been completed, and a sacrum of five vertebrae by coalescence results. 



