556 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
and there the spine is 1 inch in thickness and 1 inch 7 lines in fore-and-aft extent. The 
anterior orifice of the neural canal (Plate XL'VII. fig. 3, n) is 3 inches 5 lines in transverse 
diameter, but only 1 inch vertically between the centrum and summit of the neural arch ; 
and this dimension is rather lessened at the middle of the canal by a slight rising along 
that part of the neural surface of the centrum. A medial vertical ridge with a depression 
on each side marks the fore part of the base of the thick neural spine (ns i,). The frac- 
tured base of the prezygapophysis ( z ) of the first sacral measures 2 inches 4 lines by 1 
inch 5 lines. 
A partial ossification extends from the base of the neural spine of the first to that of 
the second sacral (ib. fig. 2 , ns i & 2 ), bisecting a deep triangular depression, which, how- 
ever, does not communicate with the neural canal ; a continuous ossification from the 
first to the second sacral neural arch forms a smooth unbroken ceiling to the canal. 
The posterior outlet of the neural canal (ib. n!) of the second sacral is transversely extended, 
3 inches 6 lines across, 10 lines in height on each side the mid rising of the centrum. 
A greater proportion of the neural spine (ns 2 ) of the second sacral than of the first is 
broken away ; the remaining base gives 1 inch 8 lines in fore-and-aft extent, 10 lines in 
greatest breadth, which is at the hind part ; the fore part is ridged with a small depres- 
sion on each side. The irregular ossification is continued from the median ridge to the 
antecedent spine. 
Of both ilia a large proportion has been preserved. The acetabular part ( 0 ) swells out 
from the body of the bone, before (fig. 1 ) and behind (fig. 2 ), and developes a tuberosity 
(d) oblong lengthwise, triangular transversely, at the upper or anterior part of the brim 
of the cavity. I 11 advance of the acetabulum the ilium contracts, especially from the 
neural to the htemal aspect, or is depressed and lamellifornr ; but continues thickest 
medially to form the junction with the sacrum, and contracts laterally to a smoothly 
rounded concave margin (ib. figs. 1 & 2, n). About the sacro-iliac symphysis the medial 
and anterior border, or “crista” of the ilium (c) contracts to a thickness of 1 ^ inch, and 
where it is entire is convex and roughened. At the fore part of this symphysis is an oval 
foramen, 1 inch by 9 lines in diameters (ib. fig. 3, f), the outlet of a canal communicating 
with the capacious intervertebral canal. The free portion of the ilium is lamelliform, 
arches outwardly, the thin outer or hinder border (n) describing a bold concave curve. 
Save for two inches near the symphysis of the right ilium, the crista is broken away. 
The hsemal surface of the iliac plate (fig. 1, 62 ) is almost flat. Transversely, it is convex 
one-third of the extent from the fractured margin ( c ), concave to the opposite outer 
margin (a, n ), both curves being feeble ; lengthwise it becomes concave toward the ace- 
tabulum. The haemal tract (p,jo) °f ^ ie sacro-iliac symphysis forms a low broad smooth 
convex ridge, enlarging and slightly rising as it approaches the acetabular part of the 
ilium, but subsiding before this begins to expand ; this ridge, or tract, feebly represents 
the “ linea ileo-pectinalis.” It seems to be suddenly resumed by a process ( e ) at the 
junction of the ilium with the acetabular end of the pubis (<u). I infer, at least from its 
being broken off on each side of this pelvis, that it projected far enough to be called 
