241 
off. The bodies of the sacral vertebra diminish in breadth to the third (fig. 6, c), where 
the sides converge to a ridged inferior termination; they then expand to the seventh, 
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 vertebra 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 vertebrie send parapophysial 
abutments (p, p) against the ilia (, 7), of which the seventh is the shortest and thickest, 
affording 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 vertebra (Pl, LX VII. fig. 5, ns). 
The long iliac bones (fig. 5, 62), as they extend from their anterior border backward, 
converge, to coalesce with the ridged summits of the spines of the first seven sacral 
vertebree, 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. 5,0). The ilia, at their fore part, do not extend 
outward beyond the parapophysial abutments of the anterior sacral vertebra, 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, | inch 2 lines 
in diameter, with an irregular, oval vacuity of 1] 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, subtrihedral 
part of the ilium, strengthened by the three longest abutments (fig. 6, p, p) of the posterior 
sacrals. The ischium (fig. 7,63) contributes the lower and posterior third of the ace- 
tabulum: the pubis (64) was attached to about one-fifth of the lower part of the cavity, 
