492 PROFESSOR OWEN ON THE SPECIES OF PHASCOLOMYS. 
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. 
The trapezium (¢) presents a concavity to the scaphoid (s/), a convexity to the meta- 
carpal of the pollex (m1.), and a concavity for the contiguous border of the base of the 
metacarpal of the index (m I1.). 
The trapezoides (z) supports the metacarpal of the index (m 1:) on the major part of 
its distal surface, and applies the rest to the radial extension of the magnum (m); it 
also articulates with the trapezium and the scapholunar. 
The magnum (m) pushes its head between the lunar part of the scapholunar (/) and 
the unciform (wz), so as almost to touch the cuneiform, but leaves a small part of both 
those bones for mutual union, as in the Beaver, The expanded distal end of the magnum 
offers a very slight concavity to the broad base of the third metacarpal (m I11.); it also 
contributes a facet to part of that of the index (m I1.). 
The unciform (w) touches the ulnar margin of the scapholunar(s/), presents a triangular 
convexity to the cuneiform (cw), mainly supports the metacarpals of the fourth and fifth 
digits at its distal surface, and touches, there, the outer extension of the base of the mid 
metacarpal, 
The metacarpal of the index (m 1.) has its base extended ‘ proximad,’ to be wedged 
between the trapezium and pollex, on one side, and between the magnum (7) and medius 
metacarpal, on the other side, but is mainly applied to the trapezoides (z). 
The outer or ulnar part of the base of the mid metacarpal (m 111.) is similarly extended 
and interposed between the base of the fourth metacarpal and the magnum (i), so that 
the three chief metacarpals overlap, interlock, or wedge each other firmly into their 
places, adding, of course, to the strength and power of resistance of this main part of 
the fossorial foot. The comparatively narrow base of the metacarpal of the ‘ minimus’ 
(m v.) is wedged between that of the fourth metacarpal and the unciform (7). 
The numerical character of the digital phalanges adheres to the mammalian formula. 
The proximal ones of the three outer digits are shorter in proportion to their breadth 
than those of the thumb (I.) and index (11.), as are also the second phalanges(2). The 
ungual ones (3) are larger than the two preceding phalanges (2,1) in the three outer 
digits l11., IV., v.; they are depressed and subtruncate at the free end on each side the 
lever of insertion (fig. 7, f) of the flexor perforans tendon; they are subdepressed and 
' subtruncate at the free end, near which the bone shows many small vascular perfora- 
tions, indicative of the rich supply of material for the quickly worn digging claws. 
