369 



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 impressed 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 platyrhinus than in Phasco- 

 lomys latifrons, 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. CI. figs. 9-11, g), presents, as in this production at the inner side of its base, 

 a strip of smooth articular surface (PI. CIII. 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. XC1X. figs. 8, 9, 10) consists of the usual seven bones — 

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

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

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

 astragalus, tibia, and fibula" 1 . 



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, ±) ; posteriorly 

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

 calcaneum, and externally with the small flattened facet for the cuboid (b), which is 

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



The astragalus (PI. XCIX. 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 l), 

 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 

 narrow tract (fig. 9, 5) with the tibial malleolar surface (fig. 8, d), and below with the 

 surface articulating anteriorly with the cuboid and continued backward expanding 

 (fig. 9, a) to rest upon and articulate with the calcaneum. 



The calcaneum (PI. XCIX. fig. 8, cl, and fig. 10) has three articular surfaces on its 

 expanded tarsal or articular half: — one above, feebly convex, sub triangular in shape 

 (fig. 10, a), for the astragalus ; one anterior, concave (b), for the cuboid ; and a narrow 

 slip continued therefrom to the inner side of the bone for articulation with the scaphoid. 

 The posterior fulcral or ' sesamoid' part of the bone (ib. ct) is triedral, broad, and 

 1 " Osteology of the Marsupialia," Zool. Trans, torn. cit. p. 406. 



