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The bone is reduced to transparent thinness between the coronal (o) and anconal (p) 

 depressions ; but I have not noticed a vacuity here in either of the continental species, 

 as in one individual of the Tasmanian Wombat 1 . 



The figures 1-4 of PL CI. will supply other features of the bone, not noted in the 

 text, which has been purposely restricted to the salient differential characters of the 

 humerus in the two continental species of Phascolomys, most likely to be available in 

 the determination of fossils. 



The radius of Phascolomys latifrons (ib. figs. 5-8) is a strong bone, slightly bent, 

 with the convexity forward ; the head (fig. 7) is subcircular and concave for adap- 

 tation to the humeral ball (ib. fig. 1, 1). From the outer side of the head a narrow 

 semielliptical convex surface ('lesser sigmoid cavity' of Anthropotomy) (figs. 5 & 6, a) 

 is adapted to the radial concavity of the ulna (fig. 11, e). A few lines below the neck 

 of the radius projects a large tuberosity (figs. 5 & 6, b) for the biceps. 



The shaft gradually expands as it descends, and assumes a triedral shape ; a ridge 

 (fig. 5, c) for the insertional fascia of the ' supinator longus ' defines at the lower third 

 of the shaft the fore from the inner surface of that part of the bone. This ridge leads 

 to a small tuberosity (d) above the base of the short thick styloid process (e). The 

 interosseal ridge or angle is well marked, and shows a rough tract at its middle third 

 (fig. 6,/'). The broad distal articular surface (fig. 8) is gently convex from before 

 backward, concave from side to side ; it is adapted to the large scapho-lunar carpal 

 bone, and to the radial facet of the cuneiform. 



The head of the radius is less circular in Phascolomys platyrhinus than in Phase, 

 latifrons, and the bicipital tubercle is rather nearer to it ; the entire bone is less thick 

 in proportion to its length ; but the differences are not such as to call for a drawing of 

 the bone in this species. 



The ulna (ib. figs. 9-11) in both Wombats is remarkable for the length and breadth 

 of the olecranon (a, a'), and for the concavity (b) continued from its ulnar (inner) side 

 (figs. 9, 10) downward below the proximal articulation. This presents three con- 

 tinuous facets — one (fig. 11, c) for the ulnar division (fig. 1, m) of the humeral articu- 

 lation, one (fig. 11, d) for the back part of the radial division of the same (fig. 2, I), 

 and the third (fig. 11, e) for the side of the head of the radius (fig. 5, a). 



The thick hind border of the olecranon contracts into the sharper hind border of the 

 shaft of the ulna, which is compressed, rounded, and thicker anteriorly, gradually nar- 

 rowing from before backward to the distal end, which suddenly contracts to form the 

 base of the short obtuse 'styloid process' (g). The ridge (fig. 11, f) opposing the 

 interosseal one of the radius, begins below the radial articular cavity, and projects as it 

 descends along the radial side of the anterior border of the ulna, developing a rough 

 facet at its middle third, which is bound by strong ligaments to the corresponding surface 

 (fig. 6,/") on the radius. On the radial side of the extension of the bone supporting 

 1 " On the Osteology of the Marsupialia," torn. cit. p. 401. 



35 



