368 PROFESSOR OWEN ON THE GENUS DINORNIS. 
2 inches 3 lines from their origin; they recommence, to be continued with partial 
thickening to the hind end of the coalesced ilium and ischium, dividing its horizontal 
from its vertical surface. 
The “pelvic disk” is deeply impressed along the middle of its anterior half, the 
channel or groove contrasting with the iliac ridge in advance. The bottom of the 
channel is entire, slightly widening as it recedes and descends, when the depressed 
spineless upper surface of the neural arches of the last three sacral vertebrae come into 
view at n, fig. 1, Pl. XLII., between the hind parts of the ilia. The sloping sides of the 
interiliac groove are pierced each by three interneural foramina. The fore part of each 
side of the pelvic disk is convex transversely ; but this changes to a concavity as it recedes. 
Of the ischial and pubic elements the broken origins are preserved at 63, 64, P]. XLII. 
fig. 1, Pl. XLIII. fig. 2. That of the pubis has a long diameter of 5 lines, where it 
extends from below the acetabulum. Where the ischium becomes free, half an inch 
below the postacetabular facet, it is 4 lines by 23 lines in thickness. 
This facet (ib. 6) is a more continuous part of the general acetabular cavity than usual. 
Including it therein, the long diameter (from before backward) measures 1 inch 4 lines ; 
the vertical diameter of the acetabulum proper is barely 1 inch ; the acetabular vacuity 
(ib. a) has a diameter of half an inch; its margin projects, as usual, into the prerenal 
or interacetabular fossa. The vertical diameter of the postacetabular facet is 6} lines. 
Between the margin of the acetabulum and the free part of the ischium (63) is a well- 
defined (antischial) fossa (Pl. XLII. fig. 1, ¢). The ischial foramen is subcircular, 8 to 
9 lines in diameters. On the right side a distal part of the ischium, coalescent with 
the ilium, is preserved, descending vertically at right angles with the area of the “ disk,” 
and effecting, by an inwardly extended plate (Pl. XLII. fig. 2, v) underlying part of the 
postrenal fossa, a bony union with the depressed terminal sacral vertebra (ib. 19). ‘The 
degree of coalescence of the sacrum and iliac bones is such as to reduce the ilio-neural 
canals to small separate spaces (Pl. XLIII. fig. 4, 7d), into which the interdiapophysial 
foramina (fig. 2,7 d) open. 
The pelvis of Aptornis differs from that of Dinornis' in its greater length relatively 
to the breadth, in its less sudden and minor expansion behind the acetabula, in the 
inferiorly carinate anterior centrums, in the more sudden expansion of the hindmost 
centrums, in the more convex contour and sharper upper ridge of the coalesced pre- 
acetabular plates of the ilia, in the deeper and narrower channel dividing the post- 
acetabular parts of the same bones, in the relatively narrower interval between the 
postacetabular parts of the ilium and ischium, and in the relatively smaller ischial 
foramen?. The rather sudden down-sinking of the preacetabular iliac ridge into the 
superacetabular iliac channel is also very significative of the distinction of ordinal 
groups between Aptornis and Dinornis. 
’ Compare Pl. XLII. figs. 1 & 2, and Pl. XLITII. figs. 1-4, with pls. 19, 20, 20 a, of vol. iii. Trans. Zool. Soc. 
> Compare Pl. XLITI. fig. 1, with pl. 20. (tom. cit.) figs. 1 & 2. 
