shufeldt: osteology of the steganopodes 123 



12tli, and still more so on the cervico-dorsals, where there coexists with it the barest 

 suspicion of lateral spines. 



Viewed dorsad, the third cervical appears to have a quadrilateral form, which 

 passes to the more oblong shape in the fourth, and the bones of this part of the 

 column commence to shorten antero-posteriorly with sixth, they being wider than 

 they are long for the remainder of the spinal series. The last two cervico-dorsals 

 develop a low, quadrilateral neural spine, which resembles, but is antero-posteriorly 

 shorter than the same process as it occurs throughout the dorsal vertebrae. 



P. fiavirostris has a delicate, osseous, interzygapophysial bar, extending from the 

 back of either prezygapophysis backwards and inwards to the corresponding ante- 

 rior bases of the postzygapophyses, in the fifth, sixth and seventh cervical vertebrae. 

 Usually it only ossifies in the fifth and sixth in P. xthereus, its place being taken by 

 ligament in the seventh and eighth. No such character as this is ever present in 

 any of the Sididse. Strong and broad diapophysial processes are first pronounced 

 in the first and second cervico-dorsals ; in the last cervico-dorsal these processes are 

 markedly shorter and shallower, while throughout the dorsal series of vertebroe they 

 are decidedly slenderer, and in their vertical diameters of very little thickness. 



Passing to the dorsal series of vertebrae, we find in P. fiavirostris six of those bones 

 freely articulated with each other between the last cervico-dorsal and the leading 

 one in the consolidated pelvic sacrum. This last-mentioned vertebra, in all my 

 specimens of P. ssthereits, coossifies with the anterior sacral, though, as we shall see 

 presently, this difference does not affect either the number or the arrangement of 

 the thoracic ribs. Hypapophyses are fairl}^ well developed upon all the dorsals of 

 the middle of the back, but they become small as we near the pelvis, to be very 

 inconspicuous or entirely absent from the last one or two bones. Pneumaticity 

 characterizes all the vertebrae between the atlas and the first caudal, and the centra 

 of the dorsals are but moderately compressed in the transverse direction. They 

 present the usual ornithic plan of articulation with each other, and the same may 

 be said of the manner in which the true ribs are connected with the segments of this 

 division of the spinal column. There are five pairs of these ribs that bear uncinate 

 processes, firmly attached to the middle of their hinder borders, and each pair of 

 these appendages is slender, sHghtly overlapping the succeeding rib in every case 

 save the last, which may or may not be of sufficient length to do so. As for the 

 ribs themselves, they, too, are long and narrow, sweeping well backwards, a fact that 

 entails the presence of lengthy haemapophyses to reach the sternum. These latter 

 are of no great caliber ; the first pair being nearly straight, and the succeeding pairs 

 becoming gradually more carved as we approach the last ones, which are the most 



