367 



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 (k) 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 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, 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 platyrhinus (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 (PI. CM. 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 (f), 

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

 (ib. A), 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 works on the 'Archetype of the Vertebrate Skeleton,' 8vo, 1846, and on 

 the 'Nature of Limbs' (pi. 1. figs. 15 & 16). 



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

 surface (a, b) for the condylar articulations of the proximal limb-bone (fig. 4, k, 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, d, e) is the homotype 

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

 ulna (ib. fig. 11, e). 



As in the radius, the shaft of the tibia (PI. CM. figs. 5-7) is compressed (fig. 7), 

 slightly bent (figs. 5, 6), with the concave border rather sharp ; and the shaft gains 

 thickness as it approaches the distal end. 



The proximal end (fig. 8) retains the usual superior extent of articular surface in this 

 bone of the hind limb as compared with its homotype in the fore limb. The surfaces 

 (a, b) adapted to the femoral condyles are partially divided posteriorly by a shallow 

 groove (c), the sides of which, especially the inner one, rise to give attachment to the 



