496 PROFESSOE OWEN ON THE SPECIES OF PHASCOLOMTS. 



summit of the lever retains its individuality and articular union with the basal part of 

 the uprising process. 



The proximal articular surface of the fibula has one facet (fig. 11, d) for the outer 

 condyle of the femur, and a rather more concave sxirface {e) for the contiguous lateral 

 facet or the proximal end of the tibia (fig. 6, a). The articular surface (figs. 10, 11, a) 

 for the ' fabella' (ib. ib. b) is subcircular and almost flat. 



The proximal half of the fibula is triedral; the outer facet (fig. 10, f) between 

 the homotype of the olecranon (a) and the antero-extemal ridge [g) is deeply concave, 

 repeating the character of the homotypal facet of the ulna, the concavity in both 

 being transverse. The anterior facet is slightly concave and of less longitudinal extent ; 

 the inner facet (fig. 11, h) is feebly convex transversely, with low longitudinal ridges 

 and imjn'essed marks of muscular attachments. 



The distal half of the shaft beomes more cylindrical, though with indications of the 

 three facets ; and these are better marked in Phascolomys platyrJiinus than in Phasco- 

 lomys latifroiis, although the fibula, like the tibia, is a relatively stronger bone in the 

 hairy-nosed Wombat. The outer malleolus (/), answering to the styloid process of the 

 ulna (PI. LXXII. figs. 9-11, g), presents, as in this production at the inner side of its 

 base, a strip of smooth articular surface (PI. LXXIV. fig. 11, k) for the contiguous part 

 of the parallel bone (fig. 6, k). But the ' process' or produced part of the distal end of the 

 fibula is broader than its homotype, and is longitudinally grooved on its outer surface. 



The tarsus of Phascolomys (PI. LXX. figs. 8, 9, 10) consists of the usual seven bones — 

 'naviculare' (s), 'astragalus' {a), 'calcaneum' {cl, ct), 'ento-' (ci), 'nleso-' (cm), 'ecto-' 

 (ce) cuneiforms, and ' cuboid' (b), together with the peculiar marsupial accessory ossicle 

 (o) described (in Dasyurus macrurus) as " a small sesamoid bone wedged in between the 

 astragalus, tibia, and fibula"'. 



The naviculare or scaphoid (s) is transversely oblong, interposed between the tibial 

 malleolus and the astragalus above, and the three cuneiforms and cuboid below. The 

 proximal surface is transversely concave for the ball of the astragalus [a, i) ; posteriorly 

 it is continuous with a narrow tract articulating with the fore and inner part of the 

 calcaneum, and externally with the small fiattened facet for the cuboid (5), which is 

 continuous with the outer of the three facets for the cuneiforms. 



The astragalus (PI. LXX. fig. 8, a, & fig. 9) is broad, depressed, and remarkable for the 

 continuity of all its articular surfaces. The upper or proximal mid surface (fig. 8, a i), 

 gently concave transversely, convex longitudinally, slightly broadening as it advances, is 

 adapted to the horizontal terminal surface of the tibia ; the lateral facets (ib. 2 & d) 

 slope away from this surface, the inner one (d) to be adapted to the oblique one on the 

 inner malleolus, the outer one (2) with a gentler slope to the more nearly horizontal 

 facet at the distal end of the fibula. The anterior convexity ( 4 ) fits into the concavity 

 of the scaphoid, touching also part of the cuboid ; it is continuous internally by a 

 ' " Osteology of the Marsupialia," torn. cit. p. 406. 



