PEOrESSOlt OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 



557 



a " process" rather than a " tuberosity." The fractured base is oblong, 1^ inch by-9 lines. 

 The process so indicated answers to that called "ilio-pubic" in Poephaga*. 



The neural surface (Plate XLVII. fig. 2, 62) of the free part of the ilium is almost as 

 flat as the haemal surface ; lengthwise the general slight convexity changes to a concavity 

 as it approaches the acetabulum ; transversely the surface becomes gently convex towards 

 the thin concave border [n). 



The nem-al surface of the ilium is divided into a rough and a smooth part ; the latter 

 is exterior, narrow, extending about 1^ inch from the external border (n), becoming 

 gradually narrower to within 4 inches of the precotylar tuberosity {d), where the smooth 

 tract ends ; the rest of the neural surface of the iliac plate is chiefly roughened by coarse 

 grooves and low ridges, mostly inclining lengthwise with more or less obliquity, indi- 

 cative of coarse and strong muscular attachments. 



At the inner and back part of the sacro-iliac symphysis an angular tuberosity, answering 

 to the " posterior inferior spine," unites with a larger rough tuberosity from the transverse 

 process of the second sacral vertebra, together forming a large " sacro-iliac " tuberosity 

 (ib. u), overhanging the deep and wide groove at the fore or upper part of the great sacro- 

 sciatic notch (m). The plane of the long curved lamelliform ilium is thus almost hori- 

 zontal, or with surfaces looking neurad and hsemad ; the long axis of the bone forms 

 with that of the sacrum an angle of 35° (Plate L. 62, s). 



Of the ischium (ib. figs. 1, 2, 4, 63) the spine is represented by a slightly promi- 

 nent surface (Z), roughened at its upper and lower margins, of an oval form, 2 inches by 

 1 inch in diameters, the long one being in the direction or axis of the ischium, and the 

 small end of the oval is forward. Between the upper part of the "spina ischii " and the 

 neural margin of the acetabulum is a low subcircular rugous tuberosity (fig. 2, q) 

 1 inch in diameter. The back or neural wall of the acetabulum contracts as it retro- 

 grades, the part contributed by the ilium being broader than that by the ischium. 



The acetabular part of the innominatum contracts transversely, and expands in the 

 neuro-hgemal direction from the line m, d to the line I, t. 



The ischium as it is produced backward beyond the acetabulum contracts, but is 

 rounded and thick posteriorly, and is thinned off" only anteriorly where it forms part of 

 the margin of the " foramen ovale." The ischia diverge from each other at this part, 

 instead of retrograding parallel with each other as in Macropus ; but to what extent is 

 not shown in the present specimen. 



The great sacro-sciatic notch (figs. 1 «& 2, m, I) presents a deep and wide groove (m) 

 at the fore part, overhung by the produced hind part of the sacro-iliac symphysis (%), 

 which symphysis is here obliterated by anchylosis. Below the groove the back part of 

 the acetabulum makes convex that part of the margin of the notch, which margin is again 

 concave slightly to the tuberosity representing the ischial spine (Z). 



* Ostcol. of Marsupialia, torn. cit. p. 403 : the shares taken respectively by the ilium aud pubis in the forma- 

 tion of the ilio-pubic process is shown in the ' Cy lopaedia of Anatomy,' 8vo, vol. iii. (1841), Art. MarswpiaUa, 

 p. 284, fig. 110 (^Hypsiprymnus). 



