359 



their expanded distal halves of the first and second, and by a less proportion in the third 

 and fourth sacrals, leaving vacuities (sd l-sd 3) between their proximal portions, into 

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

 anchylosed in the specimen figured. The bodies of the sacral vertebrse (ib. fig. 1, s is 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 vertebras, 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 0) are curved 

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



In a large full-grown Phascolomys platyrhinus there are four sacral vertebras 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-grown, example of Phascolomys platyrhinus 

 (PI. XCIX. 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 

 small sacrum (d 6, d 7), according to the character of coalescence. 



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

 the proportions contributed by the first and second sacrals (d 1, d 2) are further apart 

 than in Phascolomys latifrons (fig. 2). 



In the example of Phascolomys vombatus, described in the ' Catalogue of the Osteology 

 in the Museum of the Royal College of Surgeons' (4to, 1853, no. 1814, p. 333), anchy- 

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

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

 But, in both specimens, as in the skeleton of the Tasmanian Wombat (torn. cit. p. 330, 

 no. 1792), the two anterior vertebras only are sacral by the character of abutment 

 against and syndesmotic junction with the iliac bones. 



In an old individual of Phascolomys vombatus I have seen, and figured ', a sacrum of 

 seven vertebras by anchylosis of the centrums. Of these the first four repeat the cha- 

 racters of the four sacrals in Phascolomys latifrons by coalescence of the terminally 



1 Anatomy of Vertebrates, vol. ii. p. 331, fig. 213. 



