PEOFESSOE OWEN ON THE GENUS DINOENIS. 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 thii-d sacral centrum (PI. XV. fig. 2, c), 

 where it begins to expand, as in Aptornis otidiformis (Zool. Trans, vol. vii. pi. 42. fig. 2). 



The surface for the head of the second sacral rib is small, subcircular, concave, 

 and produced. The succeeding pleurapophyses [pi) 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 (PI. XV. fig. 2, 64). There are consequently six pairs of 

 interapophysial vacuities (ib. id. u.) at the antacetabular part of the pelvis. The mid 

 tract beneath the centrums gains a breadth of J 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 9J lines to the eleventh 

 vertebra, beyond which they contract to the fifteenth, and again expand at the seven- 

 teenth (i7) to a breadth of 5 lines, which they retain, below, to the twentieth vertebra. 

 The last three of them («, n, fig. 1, PL XV.) are caudals, which, like the dorsal and 

 lumbar vertebrae at the other end of the pelvis, have become " sacral " by anchylosis. 



In the three interacetabular sacrals (PI. 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, u), where they are long and slender, and combine at their distal ends with 

 those of the twelfth, thirteenth, and fourteenth sacrals to fonn a plate or screen of bone 

 (ib. u), dividing the interacetabular depression [t) from the postacetabular or postrenal 

 one (m). The parapophyses of the fourteenth (ib. fig. 2, u), 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 vertebrae. 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 (PI. XV. fig. 2, u), extending from the ischium 

 and confluent part of the ilium inward or mesiad to join the hinder sacral vertebra 

 (ib. c, 17), led me to examine the pelvic viscera in a recent Ealline {Rallus aquaticus) 

 with a view to determine the nature of the contents of the homologous ilio-ischial 

 postacetabular excavation in that bird. 



