494 PROFESSOR OWEN ON THE SPECIES OF PHASCOLOMYS. 
triedral below that cavity, and then rapidly expands into a long and large subquadrate 
plate of bone (63'), the hinder angle of which (/) is thickened and produced upward with 
a curve bounding there the long sacro-sciatic notch, which is not divided by any ‘spine 
of the ischium.’ This, however, is indicated by a feeble ridge or production of the hind 
or upper border of the ischium (at J, figs. 3 & 4). : 
The bare-nosed Wombat differs from the hairy-nosed species in the greater production 
of the iliac angle (a, fig. 2), and in the narrower less robust body of the ilium (62, z); in 
the greater length, minor breadth, and less definite bipartition of the articular surface 
for the sacrum (compare figs. 5 & 6); in the minor development of the ilio-pubic pro- 
cess (fig. 4, ¢) and of the ‘ rectus tuberosity’ (fig. 2, d); in the longer and more slender 
pubis (fig. 4, 64), in the shorter ridge (/:) for the marsupial bone; in the larger obturator 
foramen (0), and the absence of the projection from its ischio-pubic margin (as at v, 
fig. 3); in the narrower ischium, prior to the expansion (63') of the great tuberosity 
(h, h'); in the minor extent of that expansion, which, in Phascolomys platyrhinus, is 
rather triangular (fig. 4) than quadrate as in Phascolomys latifrons (fig. 3, 63'). The 
twist of the innominatum is not carried so far in Phascolomys platyrhinus as in Phas- 
colomys latifrons, whereby in the bare-nosed species part of the sacral plane (fig. 4, 62*) 
of the ilium is brought into view when that of the ischium (63') isin direct view; whilst 
the outer or lower border only (fig. 3, ¢) of the ilium meets the eye in this position of the 
bone in Phascolomys latifrons; and this border is thicker in Ph. latifrons than in Ph. 
platyrhinus. There are slight differences in the acetabulum: it is rather deeper in 
Phascolonys platyrhinus (fig. 4,7, 7); and the entering groove (y) is narrower in the 
bare-nosed than in the hairy-nosed Wombat (fig. 3, 7). 
Bones of the Hind Limbs.—The femur (Pl. LXXIV. figs. 1-4) is thicker in proportion 
to its length in Phascolomys latifrons than in Phascolomys platyrhinus. Both trochanters 
(d, g) are rather more prominent; but the generic characters of the bone, as e. g. depth 
of the post-trochanterian fossa (fig. 2, ¢), production of subtrochanterian ridge (f), 
longitudinal extent of trochanter minor (9, q'), flattening of the back part of the shaft 
(ib. A), community of rotular (fig. 1,2) and condylar (fig. 2, 4, 7) articular surfaces, are 
closely preserved in all Wombats. 
In the genus Phascolomys the two bones of the ‘cnemion’ or leg, bear a closer resem- 
blance and a nearer relative proportion to their homotypes in the forearm than in any 
other mammal. ‘They were selected, on that account, to exemplify such homotypal rela- 
tions in my work on the Archetype of the Vertebrate Skeleton (Pl. LXIX. figs. 15 & 16). 
The head of the tibia (Pl. LX XIV. fig. 8), like that of the radius, presents a horizontal 
surface (a, 6) for the condylar articulations of the proximal limb-bone (fig. 4, /, 7), and a 
smaller vertical articular surface (fig. 6, ¢) for the contiguous bone; this surface for the 
lower division of the proximal articulation of the fibula (fig. 11, d, e) is the homotype of 
the surface in the radius (Pl. LX. XII. figs. 5 & 6, a) for the ‘ lesser sigmoid cavity’ of the 
ulna (ib. fig. 11, e). 
