• SiiriKi.nr: Osteology of im-. 1m,.\min(;<)Ks. 309 



forwards and on its mesial aspect are seen the pneumatic foramina. 

 This peculiar expansion becomes much less as we pass through the 

 series in the direction of the pelvis, but is never entirely lost ; while 

 on the other hand the unciform processes become enormously elon- 

 gated and widened, being anchylosed to the ribs. But these again in 

 turn are a little less conspicuous as we approach the pelvis, and the 

 pelvic ]iair of ribs are without them entirely. The cosfa/ ribs are 

 slender and flattened, and not much curved, with the exception of the 

 ultimate pair, and even they do not show it as much for their lengths, 

 as in some other birds. Measuring the chord of one of these last, it 

 is seen to be d.^^ cm. long, while the length of one of the first i)air 

 is not more than 1.7 cm. 



The /(?/<'/> of PliKnicoptenis is inclined to be rather narrow, or at least 

 moderately so, and deep in the vertical direction. Viewed upon its 

 dorsal aspect, the superficial area of the preacetabular region is about 

 equal to the postacetabular, but the latter is nearly flat in character, 

 while the sides of the former are somewhat concave, and face far 

 more outwardly than u])wardly. The long, median axis of the 

 sacrum is almost a straight line. Anteriorly, the borders of the 

 ilia are much rounded, jagged in character, emarginated, and these 

 bones here overarch the first sacral vertebra, to a considerable degree. 

 A double row of intervertebral vacuities are present, the first half dozen 

 pairs being all more or less of a size, but posterior to them, the last 

 two sacral vertebras become far more individualized — the ultimate one 

 being very distinctly so, projecting as it does beyond the iliac bones 

 posteriorly. 



In the preacetabular region the mesial margins of the ilia meet over 

 the toj) of the sacral crista only at their middle points, and these bones 

 in this locality are completely fused with the sacrum — the ilio-neural 

 canals being thus thoroughly covered over, and sealed up both in front 

 and behind. As these iliac borders sweep round in the direction of 

 the acetabulum upon either side, they are seen to be roughly sharpened 

 and rather prominent. Over either ilio-ischiac foramen the ilium is 

 seen to jut out in the horizontal plane, thus forming an overhanging 

 ledge above that vacuity, of a fairly well-marked character. Below, 

 as well as in front of this projection, and especially above and in front 

 of the cotyloid ring, the bone is wrinkled, and puckered, and pitted, 

 the various little concavities thus formed harboring at their bases the 

 pneumatic foramina that lead into the internal tissue of the pelvis. On 



