PROFESSOR OWEN ON THE SPECIES OF PHASCOLOMYS. 485 



more convex than in any of the other ribs ; and this fits the deep cup on the diapo- 

 physis of the first dorsal vertebra (ib. fig. 6, d!). There is a rough low tuberosity (ib. 

 fig. 7, d) on the middle of the outer or anterior surface of the first rib for the attach- 

 ment of a strong scalenus muscle. In the second rib (ib. fig. 8) besides the head [a), 

 neck (c), and tubercle {b), there is, on the outer border, at the same distance from the 

 tubercle as this is from the head, a second tubercle or process {e), smaller than the 

 normal one {b), and serving exclusively for muscular attachment; it answers to what is 

 called the ' angle of the rib ' in anthropotomy. The articular surface on the tubercle 

 is flat (6), as in all the succeeding ribs possessing it ; anterior to this surface is a tubercle 

 for the attachment of the costal ligament. In the fifth rib (ib. fig. 9), besides the 

 process holding the same relative position to the tubercle as in the second rib, there is 

 another (/") at a greater distance, which answers better to the 'angle.' 



The neck (c) shortens as the ribs recede in position, and disappears with the loss of 

 the articular tubercle in the last three pairs. The longest ribs are the seventh and 

 eighth pairs in Phascolomys latifrotis. The hind border of the proximal third of the 

 shaft is slightly produced, indicative of an ' intercostal groove.' The shaft is flattened 

 and expanded at its distal end {g and fig. 9'), which is twisted at right angles to the 

 broadest part of the neck of the rib. This terminal expansion (fig. 9') is lost in the 

 three last pairs (fig. 10). Six anterior pairs of rib-cartilages (PL LXIX. fig. 11, h, i-e) 

 articulate directly with the sternum, which consists of six bones, including the manu- 

 brium (m) and xiphisternal {x). The fourth and fifth sternebers coalesce earlier than 

 any of the others ; the articulation of the cartilages of the fifth pair of ribs ( 5 ) indicates 

 the place of the harmonia and the shortness of the fifth stemeber compared with the 

 rest ; its antero-posterior thickness is considerable, and increases as it recedes (as shown 

 in the side view (PI. LXIX. fig. 11 a, i). The cartilages of the sixth pair of ribs {h, 6) 

 articulate to the lower angles ; and the inner or hind border alone affords attachment to 

 the xiphisternal {x). The manubrium (ib. fig. 11, m)\s subcarinate, and affords oblong 

 syndesmotic surfaces for the strong clavicles. 



Phascolomys, like all the other genera of Marsupialia of which the vertebral formula 

 is known, has twenty-six vertebrae between the skull and sacrum. The nineteen ver- 

 tebrae following the seven cervical vary as to the number of the pleurapophyses deve- 

 loped as movably articulated ribs. In the two examples of Phascolomys platyrhinus of 

 which I have had the opportunity of examining the entire skeleton, fifteen vertebrae 

 sustain such pairs of ribs, leaving four vertebrae as ' lumbar ;' and this was the formula 

 presented by the corresponding part of the vertebral column of the Phascolomys vombatus 

 described in a former Paper'. In the only complete skeleton oi Phascolomys latifrons 

 which has yet reached me the number of lumbar vertebrae is six. In this formula it 

 deviates less from the rule of ' dorsal ' and ' lumbar ' vertebral notation in the mar- 

 supial order than do the bare-nosed Wombats of Tasmania and Australia. 



' Trans. Zool. Soo. vol. ii. p. 395, pi. Ixviii. 



VOL. VIII. — PAKTViii. April, l^li. 3y 



