490 PEOFESSOR OWEN ON THE SPECIES OF PHASCOLOMTS. 



the interval obliquely downward and inward, expanding and becoming lost upon the fore 

 part of the broad distal end of the bone. 



At the back or anconal part (ib. figs. 2, 4) the head of the humerus (a) is seen to 

 descend lower and in a more angular form in Phase, latifrons (fig. 2, a) than in Phase, 

 platyrhinus (fig. 4, a). The short transverse ridge for the humeral head of the triceps 

 is most strongly marked in Phase, latifrons (fig. 2, n). The margin of the supinator 

 ridge is thicker, and is bent forward in the bare-nosed species (fig. 4, h). 



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'. 



The figures 1-4 of PI. LXXII. 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 (PI. LXXII. figs. 5-8) is a strong bone, slightly 

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

 adaptation 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, J) 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,y). 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 (Plate LXXII. 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, ?«) of the humeral articu- 

 lation, one (fig. 11, rf) 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 

 ' " On the Osteologj- of the Marsupialia," torn. cit. p. 401. 



