(t I'achifpoil pi'iii tin: i'tunhndijt li>jn.r (i rt.>ustiud. .517 



riil_i;«' has beooiuo dcpirsst-d, aiul the side is roiUKled, so that 

 the tiattened artirular end has an aspect ot' beiii^^ a little eoin- 

 pressed from side to side. 



These vertebriv, it" really belonging to the same individual 

 as the foot-bones, would indicate a smaller and more mammal- 

 like tail than that attributecl to the other Dinosaurs. Jud^MnLT 

 fn»m Prof. () wen's ri,:,nn-es (Paheont. 1802), the early caudal 

 vertebra' of StrlidosiiiirKs liave the centrum more obliijuely 

 inclined forward, a neural arch with a lonL,a'r attachment, 

 lon«;er and stronger transverse processes placed more anti-riorly, 

 ami an absence of ridges on the side of the centrum, wjiieh has 

 the articular margin more thickened ; but the absence of ridges 

 from the centrum is the most marked character of Scelido- 

 saurm^ which distinguishes its caudal vertebrte from those of 

 this animal. 



The caudal vertebra of Hi/l(POsaurus have not been figured 

 by Prof. Owen. 



The caudal vertebra? of Jl^psi/ophodon, so far as can be 

 judged from Prof. Owen's figm-e (Palieont. 1854, pi. 1), ajipcar 

 to be not dissimilar, but have the transverse processes from 

 the centrum more developed and placed anteriorJn instead of 

 posteriorly, while the articular margins of the centrum seem 

 to be greatly developed. In Ljnanodon (Pala^ont. 1804, pi. 9, 

 and 1851, pi. 37) the resemblance to the centrum of Acaatho- 

 phoUs is much closer (supposing the figured determinations to 

 be satisfactory), and the differences would seem to be chiefiy 

 in the proportions of the bones. Presuming that most of the 

 Dinosaurian caudal vertebra from the Potton Sands are to be 

 referred to L/uanodon, it will be noticed that the centrum is 

 more elongated than in Acant/toj)huliSj and has but one ridge 

 on the middle of the side of the centrum, while the basal sur- 

 face is not so concave from front to back, nor the parts of the 

 side so concave or convex respectively from above downward. 



In Hadrosaurus the centrum, as figured by Leidy, appears 

 to be much shorter from back to front, and not likely to be 

 confounded with Acanflup/ioh's. 



On comparing the fossil with reptiles, the cup-and-ball 

 articulation, the long attachment of the neural arch, and the 

 strong transverse processes (not to mention the number of 

 verfebrge) show the tail of lizards to be well distinguished 

 from AcantJiojyJiolis. In Chdydra {Emysaura)^ where the 

 Chelonian tail is long and has the vertebra in some respects 

 comparable, the centrum is opisthocoeliau. 



Among crocodiles the articular ends of the centrum are 

 flattened instead of being concave, and the centrum differs in 

 most of its details ; but of all reptiles the crocodile is least 

 unlike this Dinosaur, though no crocodilian vertebra? have the 



