494 PEOFESSOK OWEN ON THE SPECIES OP PHASCOLOMTS. 



triedral below that cavity, aud then rapidly expands into a long and large subquadrate 

 plate of bone (03'), the hinder angle of which (A) is thickened and produced upward -with 

 a curve hounding 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 I, figs. 3 & 4). 



The bare-nosed Wombat differs from the hairy-nosed species in the gi-eater 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, e) and of the ' rectus tuberosity ' (fig. 2, d) \ in the longer and more slender 

 pubis (fig. 4, 64), in the shorter ridge (Jc) for the marsupial bone ; in the larger obturator 

 foramen (o), 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 platyrJdnus, 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 platyi'liinus 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 ^aew when that of the ischium (63) isin direct view ; whilst 

 the outer or lower border only (fig. 3, t) 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 

 Phascolomys j^latyrhimis (fig. 4, i, 'i) ; and the entering groove (y) is narrower in the 

 bare-nosed than in the hairy-nosed Wombat (fig. 3, y). 



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, e), production of subtrochanterian ridge (/), 

 longitudinal extent of trochanter minor {g, g'), flattening of the back part of the shaft 

 (ib. h), community of rotular (fig. 1, i) and condylar (fig. 2, k, I) 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 (PI. LXIX. figs. 15 & 16). 



The head of the tibia (PI. LXXIV. fig. 8), like that of the radius, presents a horizontal 

 surface {a, b) for the condylar articulations of the proximal limb-bone (fig. 4, Jc, I), and a 

 smaller vertical articular surface (fig. 6, e) for the contiguous bone ; this surface for the 

 lower division of the proximal articulation of the fibula (fig. 11, f7, e) is the homotype of 

 the surface in the radius (PI. LXXII. figs. 5 & 6, a) for the ' lesser sigmoid cavity' of the 

 ulna (ib. fig. 11, e). 



