238 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



orly and coalesces with the similarly expanded end of the second rib, 

 thus inclosing a siibcircular sacral foramen (/ and /% iig. 17). If 

 present, the other ribs would probably repeat this arrangement, and 

 there would be a row of at least four of these foramani — possibly 

 five, if the transverse of the first sacro-caudal reaches the intero- 

 posterior border of the ilium, which I doubt. The outer coalesced 

 ends of ribs one and two exhibit a wide articular area, looking down- 

 ward and outward, for articulation with the ilium. Two of these 

 ribs were found with specimen No. 2210, but both were detached, 

 although not far removed from their positions in the sacrum. It 

 would appear from the evidence of these two individuals that in the 

 young they remain distinct, but in the adult become completely fused 

 with the sacrum. 



After a study of these processes as represented in Camptosaunis, it 

 is at once apparent that they are derived from centers of ossification 

 entirely distinct from those which give origin to the centra or their 

 neurapophyses. Inasmuch as the diapophyses are distinct from the 

 sacral ribs, as shown in some individuals, there a^^pears no good 

 reason why, in this group at least, they should not be considered 

 true ribs, modified to fit the exigencies of their position. The sacro- 

 dorsal in Camptoscmrus, as in Tricei'htojjs, is considered to be without 

 parapophyses. The parapophyses of the second sacral, however, 

 might be considered the articular area on the pedicle of the arch 

 below the diapophyses, extending down on to the centrum which sup- 

 jDorts the lower articular portion of the sacral rib. The additional 

 support given this rib by the posterior area of the first sacral centrum 

 I should consider as being homologous with the demi-facets found 

 in the dorsals of certain groups of the mammalia. The fact that a 

 single-headed rib is borne by the last dorsal shows without question 

 that the first sacral rib would, as shown previously, pertain to sacral 

 one. 



"V^Tiile Hatcher " has shown the probability of the supports for the 

 ilia in the Sauropoda being the coalesced dia- and parapophyses, his 

 arguments do not appear conclusive, and in view of the evidence 

 here presented I am convinced that in Camptosaunis at least the 

 existence of true sacral ribs is fully determined. 



When the centra are articulated the ventral surface as a whole is 

 slightly arched, its outline being rendered sinuous by the constriction 

 of the middle of the centra and the prominence of their terminal 

 borders. In Camptosaurus, as shown by the sacra considered in the 

 previous pages, the sacrum is composed of either four or five vertebrae, 

 which will receive further attention in the present paper when the 

 several species are discussed. 



"Mem. Carnegie Mus., II, No. 1. Nov., 1903, pp. 21, 22. 



