WEALDEN FORMATIONS. 3 



vertebral column of a young Alligator from the fourth cervical to the first lumbar 

 vertebrae inclusive ; which vertebrae are also seventeen in number in that reptile. 

 Supposing the vertebrae of the young Iguanodon in question to be the homologous or 

 nearly homologous vertebrae to those of the Alligator compared, the characters of the 

 cervical vertebrae are given by the detached specimens, i, 2, and 3, fig. 1, and figs. 2, 

 3 and 4, forming the anterior end of the series, and the degree of curvature shown by 

 these vertebrae, which have been fixed together by the matrix, as they were naturally 

 juxtaposed at the animal's death, and the slenderness of the portions of the ribs, 

 pl, fig. 2, therewith preserved, add to the probability that they belonged to the neck. 



In my 'Report on British Fossil Reptiles,' 1841, torn, cit., p. 126, I showed 

 that the cervical vertebrae, which had been referred by Dr. Mantell to the Iguanodon, 

 on the supposition that such vertebrae had ball and socket articular extremities, 

 placed as in the neck-vertebrae of the Iguana, had, in fact, these articular surfaces 

 situated in a reverse position to those in the Iguana and most existing Saurians, 

 and that they agreed in that peculiarity with the vertebral characters which 

 Cuvier had demostrated* in an extinct Saurian genus, subsequently called 

 Streptospondylus. I had previously, however,f suggested the possibility that 

 such Streptospondylian vertebrae from the Wealden might be the cervical ones of a 

 large Saurian having plain-surfaced or concave vertebrae in the dorsal and lumbar 

 regions. The authors of the paper ' On the Osteology of the Iguanodon,' in the 

 'Philosophical Transactions' for 1849, adopting this idea,j have applied it to the 

 Iguanodon itself, but on no better grounds than a conjectural guess, which considera- 

 tions of difference in other characters and proportions forbad my hazarding, when 

 maturely considering the nature of the anteriorly convex vertebrae from the Wealden, in 

 my ' Report.' Accordingly, in regard to the cervical vertebrae of the Iguanodon, I re- 

 stricted myself to the following remark : " The desirable knowledge, therefore, of the 

 anatomy of that region of the spine in the Iguanodon, which in other Saurians is usually 

 distinguished by its w r ell-marked and varied characters, remains to be acquired." p. 126. 



* 'Ossein. Foss ,' v, pt. ii, p. 153, pl. 8 and 9. t 'Report,' Op. cit., p. 96. 



X P. 2/3. The reference to my observation is so made as to compel me to reproduce textually the 

 passage in which the- possible nature of Streptospondylian vertebrae was first indicated. "Since the 

 vertebrae of the Streptospondylus lose their peculiar convexo-concave character by the gradual subsidence of 

 the anterior ball, as they approach the tail, the cervical vertebrae of the Cetiosaurus may approach, more 

 nearly than do the dorsal ones, to the convexo-concave structure of the Streptospondylian vertebrae. The 

 fact that, hitherto, only cervical vertebrae of the great Streptospondylus, and only dorsal and caudal 

 vertebrae of the Cetiosaurus, have been discovered in the Wealden formations, has induced me well to 

 consider the grounds for assigning them to Saurians of distinct genera. But the general constancy of the 

 vertebrae of the same Saurian in their antero-posterior diameter, forhids the supposition of a vertebra of six 

 inches in length in the neck being associated with one of three inches in length in the back. Additional 

 evidence of a very decisive character must at least be obtained before the great Cetiosaur can be admitted to 

 have resembled the Pterodactyle in such disproportionate length of the cervical vertebrae." p. 96. 



