22 SHUFELDT — OSTEOLOGY OF THE CUCKOOS. [Jan. 4, 



close interlocking is evidenced among these four dorsal segments, 

 and the post- and prezygapophyses are no longer than is necessary 

 to afford the proper amount of surface for their respective articular 

 facets. Anteriorly, these face upward and inward, precisely the 

 reverse being the case with those found on the postzygapophyses. 



So far as we have examined the vertebral column, the articulation 

 which obtains among the centra is upon the hetei-ocoelons plan — i.e, 

 the anterior facet is concave from side to side, convex from above 

 downward, precisely the reverse condition being present in the 

 posterior facet. All these vertebrae, as well as both kinds of ribs, 

 are eminently pneumatic, groups of foramina occurring at the usual 

 sites in these bones. 



The Pelvis (PL I, Fig. 4). — From its singularly unique form the 

 pelvis of Geococcyx has attracted the attention of a number of 

 anatomists. Owen speaks of the ilium as forming behind "a. 

 prominent ridge in most birds, which generally overhangs the outer 

 surface ; in Geococcyx to a remarkable extent, like a wide pent- 

 house, producing a deep concavity in the outer and back part of 

 the ilium, where it coalesces with the ischium." l 



Marsh, in his classical work upon the Odoniornithes, again calls 

 attention to the same thing, and points out other particulars in con- 

 nection with it, making admirable comparisons with the pelves of 

 Peptilia, Tinamus and other forms. 2 



Strange to relate, the only other living American bird, so far as 

 I have examined, that possesses a pelvis anything like the one we 

 find in Geococcyx is the common Sora Rail (Porzana Carolina). 



This bird not only has either ilium forming the peculiar outward- 

 curling crest behind, but has also the propubis well marked and 

 identically the same style assumed by the anterior portions of the 

 ilium, i.e., a deeply concave inner margin, with the sacral crista 

 mounting above it and not coming in contact with the same. 



Viewing the pelvis of Geococcyx from above, we are to notice the 

 condition just alluded to as well as the raised anterior emargina- 



1 Anat. of Verts. , Vol. ii. p. 34, London, 1866. 



2 Marsh, O. C, Odontomithes, pp. 70-73, Figs. 16-20, Washington Govern- 

 ment Printing Office, 1880. There certainly can be nothing that advances our 

 knowledge of the exact origin of birds more certainly than the constant compari- 

 son of recent forms with the material palaeontology has thus far been enabled to 

 supply us — not a great deal as yet. Prof. Marsh never seemed to allow such an 

 opportunity to escape him. 



