NO. 166G. OSTEOLOGY OF CAMPT08AURUS—GILM0RE. 227 



face of the pedicle of the arch. Viewed posteriorly the neural canal 

 is subelliptical in outline, the longer axis being vertical. 



The most striking feature of the axis is the presence of a second 

 intercentrum firmly co-ossified with the inferior surface of the an- 

 terior extremity of the centrum. Attention has been called to this 

 element in a former pajDer " as follows : 



In compai-ins the axis of Morosaurus agilis with the homologous parts of 

 other Diuosauriau specimens in the V. S. National Museum, the writer found, 

 on the axes of two individuals of the genus Camptosaurus, intercentra attached 

 by suture to the centra of the axes. So far as tha writer is aware, this element 

 has not been observed before in a representative of the Orthopoda. In the 

 smaller (No. 5474, U.S.N.M.) and probably younger specimen the intercentrum 

 has been somewhat crushed out of position, but in the larger specimen (No. 

 5473, TT.S.N.M.) it is retained in place. * * *_ 



Inferiorly the intercentrum of Camptosaurus is roughly subelliptical in form, 

 the longer axis being tranverse. It is closely united by 

 suture to the lower half of the anterior end of the 

 centrum, forming a prominent lip-like projection which, 

 when articulated, underlaps somewhat the centrum of 

 the atlas [see fig. 12]. In a fully adult specimen this 

 element would probably become coossifled, as in Moro- 

 murus gramJis, and thus lose its identity. Viewed 

 from the side, it is triangular in form, the deepest 

 portion being next to the centrum. The inferior sur- 

 face is gently convex transversely and slightly concave 

 antero-posteriorly. Seen from the front, the center has 

 the greatest vertical depth, the upper margins gradu- 

 ally sloping down to the lateral borders. The anterior 



face is smooth and somewhat concave supero-inferiorlv. ^^^" ^'- Central view 



'■ "'of atlas and axis of 



There are two small pits on the median anterior part Camptosauuus dispak 



of the inferior surface. The presence of an axis inter- Marsh. Cat. No. 5473, 



centrum in both the Opisthocoelia (Sauropoda) and TLS.N.M. ; | nat. size. 



„ ^, , ,T^ -,.,.. , „ (it. in, ATLAS intercen- 



Orthopoda (Predentata) tends to confirm somewhat t^vm; ax, k^is; ax. in, 

 the contention of Marsh and Hatcher that the Diuo- second intercentrum ; 

 sauria is a natural group, and in the examples cited ''^ facets fob rib. 

 here it should be considered a persistent primitive character which was present 

 In a remote but common ancestor. 



The second intercentrum is also present in the typical skeleton of 

 Camptosaurus nanus, although not suturally united. 



In 1889 Lj^dekker '' called attention to the axis of a dinosaur from 

 the Wealden of the Isle of Wight, which had an axil intercentrum 

 attached to it. After comparing it with Marsh's figures of the axis 

 of Ceratosaurvs nasicornis (holotype, Cat. No. 4735, U.S.N.M.), he 

 considers the general resemblance so close as to indicate the prob- 

 ability of its belonging to the same suborder. He says : " It therefore 

 seems highly likely that it may be referable to the Wealden species 

 of Megolosaurus or to a nearly allied form." 



" C. W. Gilmore, Proc. U. S. Nat. Mus., XXXII, 1907, p. 164. 

 ^ Quart. Journ. Geol. Soc. London, XLV, 1889, pp. 44, 45. 



