398 PROFESSOR OWEN ON THE GENUS CNEMIORNIS. 



which has a broad, flattened inferior surface, rather concave transversely ; beyond this 

 they again contract, and reassume the inferior ridge, to which the flat sides converge 

 and meet at a right angle. The first and second sacral vertebrae show the subcircular, 

 shallow depressions, at the upper and anterior border of the centrum, for the long ribs ; 

 the third shows a similar, but much smaller, surface, indicative of a short and loose 

 pleurapophysis which has been lost ; the five following vertebrte send parapophysial 

 abutments (p,p) against the ilia (i, i), of which the seventh is the shortest and thickest, 

 afi'ording the chief resistance against the pressure from the acetabulum (a). The three 

 following vertebrae have no parapophyses : the lateral pairs of orifices for the separate 

 issue of the sensory and motory roots of the sacral nerves are here conspicuous ; the 

 parapophyses reappear in the twelfth sacral vertebra, and are continued on to the 

 seventeenth, mostly in the form of broad, thin, antero-posteriorly compressed plates, 

 continuous with the diapophyses, and about an inch in length in the first three, thence 

 gradually diminishing and abutting in a direction upward, outward, and backward 

 against the junction of the ilia with the osseous expansion from the neural spines of 

 the posterior sacral vertebrae (PI. LXIV. fig. 5, ns). 



The long iliac bones, as they extend from their anterior border backward, converge 

 to coalesce with the ridged summits of the spines of the first seven sacral vertebrae, 

 then rapidly diverge to the thirteenth, and again converge to the seventeenth vertebra, 

 leaving a rhomboidal space, 4 inches in length and 2 inches in breadth, where the 

 pelvic roof is formed by a thin expanse of bone (ns), continued from the neural spines 

 and the upper borders of the diapophyses to the ilia ; this part of the roof is straight 

 lengthwise, concave across, with a smooth, medial convexity formed by the summits of 

 the confluent spines, 4 lines in breadth. A few small foramina alone here indicate the 

 primitive division of the sacrum (fig. 5, o). The ilia, at their fore part, do not extend 

 outward beyond the parapophysial abutments of the anterior sacrals, but rise, at first 

 concave and then convex, to the summits of the spines ; the concavity is bounded by a 

 curved ridge, convex upward. The acetabulum (fig. 7, a) is circular, 1 inch 2 lines in 

 diameter, with an irregular, oval vacuity of II lines in long diameter ; the anterior wall 

 is deepest, having an extent of 8 lines, the posterior wall becomes reduced to 3 lines ; 

 the articular surface of the upper part of the cavity is continued upon the superace- 

 tabular prominence (6), which is applied to that upon the upper part of the femur; the 

 large ligamentous depression upon the head of the femur projected, in the living bird, 

 through the acetabular vacuity. There is a pneumatic fossa above the upper border of 

 the acetabulum : the superacetabular surface is supported by a thick, strong, subtri- 

 hedral part of the ilium, strengthened by the three longest abutments (fig. tt, /J, p) of 

 the posterior sacrals. The ischium (63) contributes the lower and posterior third of 

 the acetabulum : the pubis (64) was attached to about one-fifth of the lower part of the 

 cavity. 



