PROFESSOR OWEN ON THE SPECIES OF PHASCOLOMYS. 491 
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’ (7). 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, f) on the radius. On the radial side of the extension of the bone supporting 
the surface for the ulnar division of the humeral articulation is the mark of the insertion 
(fig. 11, h) of the ‘ brachialis anticus,’ 
The ulna of Phascolomys latifrons (ib. fig. 9) differs chiefly from that of Phascolomys 
platyrhinus (ib. fig. 10) in the quadrate form of the long olecranon (a, a’) which preserves 
its breadth to the truncate summit, while in Phasc. platyrhinus (fig. 10) it contracts to 
that summit (fig. 10, a), which is thick, obtuse, and tuberous. The hind border of the 
olecranon is thicker in Phascolomys latifrons than in Phascolomys platyrhinus. The 
surface (fig. 11, c) for the ulnar division of the humeral joint is relatively longer, nar- 
rower, and more oblong in Phase. latifrons than in Phase. platyrhinus. 
The carpus of Phascolomys (Pl. LXX. fig. 5) consists of a scapholunar (ib. s/), a cunei- 
form (ib. cu), a pisiform (p), a trapezium (t), a trapezoides (z), a magnum (mm), and an 
unciform (wv). Of these seven carpals the first and last are the largest. 
The scapholunar has the proximal articular surface (s/) traversed lengthwise by the 
obtuse ridge or angle between the anterior subconvex and posterior subconcave surfaces, 
both of which are adapted to corresponding surfaces of the radius; it articulates also 
with the cuneiform, trapezium, trapezoides, magnum, and unciform. Of the mammals 
in which a single carpal bone repeats the proportion, position, and connexions of two 
carpal bones, viz. the ‘ scaphoid’ and ‘lunar,’ in man, the most numerous instances are 
afforded by the Carnivora and Rodentia*. In the former the extent to which the unci- 
form joins the lunar part of the scapholunar resembles that in man; in the latter (Castor, 
e.g.) the extent of such junction is much less. In Phascolomys the radial surface of the 
scapholunar is broader in proportion to its length, and less convex than in Macropus; it 
contracts more suddenly to its outer end above the part extended to offer the convexity 
to the trapezium. The anconal or dorsal non-articular tract is mainly reduced to a small 
subtriangular space between the concavity for the trapezoides and that for the magnum, 
the former concavity coming almost into contact with the radial convexity, yet separated 
bya linear tract continued from the triangular portion to the trapezial process or convexity. 
The chief extent of non-articular surface is at the under or thenal aspect of the bone. 
The cuneiform (ib. fig. 5, ew) presents a concavity for the styliform process of the ulna, 
' The same letters are used as indicate the homologous bones in the carpus of Phascolomys vombatus in fig. 15, 
pl. i., ‘Nature of Limbs,’ 8vo, 1849. Neither in that species, nor in the two larger continental kinds, have I 
found a distinct os lunare. 
* Cuvier, ‘ Legons d’Anat. Comp.’ 8yo, 1835, vol. i. p. 427. 
