PROFESSOR OWEN ON THE GENUS DINORNIS. 123 
surface of the centrum is carinate; the keel beginning 2 lines behind the lower border 
of the articular surface. The keel runs to the third sacral centrum (Pl. XV. fig. 2, ¢), 
where it begins to expand, as in Aptornis otidiformis (Zool. Trans. vol. vii. pl. 42. fig. 2). 
The surface for the head of the second sacral rib is small, subcircular, concave, 
and produced. The succeeding pleurapophyses (pl) are represented by short thick 
parapophyses abutting against the lower border of the ilia, to the fifth (seventh, 
including the moveable ribs) pair, which abuts against the part to which the head 
of the pubis is anchylosed (Pl. XV. fig. 2, 64). There are consequently six pairs of 
interapophysial vacuities (ib, id. id.) at the antacetabular part of the pelvis. The mid 
tract beneath the centrums gains a breadth of 4 inch at the seventh vertebra, beyond 
which it contracts to a point at the fourteenth. 
The sacral centrums maintain their breadth to the seventh vertebra, contract at the 
eighth, but between the acetabula maintain a breadth of 94 lines to the eleventh 
vertebra, beyond which they contract to the fifteenth, and again expand at the seven- 
teenth (17) to a breadth of 5 lines, which they retain, below, to the twentieth vertebra. 
The last three of them (n,n, fig. 1, Pl. XV.) are caudals, which, like the dorsal and 
lumbar vertebre at the other end of the pelvis, have become “sacral” by anchylosis. 
In the three interacetabular sacrals (Pl. XV. fig. 2, c’) the parapophyses are, as usual, 
suppressed ; there is, however, a filamentary representative of one of those processes from 
the left side of the eighth sacral centrum. The parapophyses reappear at the eleventh 
sacral (ib. p, 11), where they are long and slender, and combine at their distal ends with 
those of the twelfth, thirteenth, and fourteenth sacrals to form a plate or screen of bone 
(ib. w), dividing the interacetabular depression (¢) from the postacetabular or postrenal 
one (uw). The parapophyses of the fourteenth (ib. fig. 2, 14), fifteenth, and sixteenth 
sacrals increase in breadth, and bend or arch outward and upward to form the lower and 
lateral walls of a passage or cavity on each side of the crest formed by the continuous 
or confluent neural spines of the corresponding vertebre. These “ ectoneural” canals 
are partially divided above by diapophysial or upper transverse plates, arching from the 
neuro-spinal crest to the inner surface of the plate or ectoneural side-wall. 
The civil engineer might study, perhaps with advantage, the disposition of the several 
buttresses, beams, and arched plates of bone which support the iliac roof of the pelvis, 
and strengthen the acetabular walls receiving the pressure of the thigh-bones, in this 
large and powerful Wood-hen. 
The unusual depth and width of the excavation at the postacetabular part of the 
pelvis, the hind part of which excavation is partitioned off from the ‘general pelvic 
cavity by a deck, as it were, of bone (Pl. XV. fig. 2, v), extending from the ischium 
and confluent part of the ilium inward or mesiad to join the hinder sacral vertebra 
(ib. ¢, 17), led me to examine the pelvic viscera in a recent Ralline (Rallus aquaticus) 
with a view to determine the nature of the contents of the homologous ilio-ischial 
postacetabular excavation in that bird. 
