3G4 



the surface for tho ulnar division of the humeral articulation is the mark of the insertion 

 (fig. 11, h) of the 'brachialia 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 Phase, 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. 



Tho carpus of Phascolomys (PI. XCIX. fig. 5) consists of a scapholunar (ib. si), a cunei- 

 form (ib. cu), a pisiform (p), a trapezium (t), a trapezo'ides (z), a magnum (m), and an 

 unciform (u)\ Of these seven carpals the first and last are the largest. 



The scapholunar has the proximal articular surface (si) 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, trapezo'ides, 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 Bodentia 2 . 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 trapezo'ides and that for the magnum, 

 the former concavity coming almost into contact with the radial convexity, yet separated 

 by a 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, cu) presents a concavity for the styliform process of the ulna, 

 to the reception of which the pisiform (p) also contributes ; the cuneiform supports the 

 rest of the pisiform, and articulates with the lunar part of the scapholunar and with the 

 unciform. 



The pisiform (ib. fig. 5, p) is a strong, thick, subelongate bone, expanded at both ends ; 

 the proximal one offers two articular surfaces for the ulna and cuneiform, the distal end 

 is simply convex and smooth ; it might be mistaken for a proximal phalanx, to which 

 it has a general resemblance ; but the form of the two facets of the proximal surface 

 distinguishes the pisiform. 



1 The same letters are used as those which indicate the homologous bones in the carpus of Phascolomys vom- 

 batus'm fig. 15, pi. i., ' Xature of Limbs,' 8vo, 1849. Neither in that species, nor in the two larger continental 

 kinds, have I found a distinct os lunare. 5 Cuvier, ' Lecons d'Anat. Comp.' 8vo, 1835, vol. i. p. 427. 



