262 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



inches long, the anterior part of the body is further indicated 

 by the position of the costal tubercle, or transverse process, 

 which is developed as a strong obtuse ridge from the middle 

 part of that half of the centrum which is nearest the convex 

 articulation." 1 



In the Memoir in the "Philos. Trans." 1849, p. 286, 

 Professor Melville enters at length on the reasons assigned by 

 Professor Owen for referring the above vertebras to the croco- 

 dilian genus Streptospondylus ; the following summary will 

 suffice for our purpose ; the British student in fossil Erpe- 

 tology, (when such an aspirant for scientific distinction shall 

 arise), I would refer to the original memoir. 2 



" The large cervical vertebrae from the Wealden strata, with 

 reversed convexo-concave joints, (Streptospondylus major of 

 Professor Owen,) enter into the composition of the cervical 

 region of the spinal column of the Iguanodon. We are led 

 to this conclusion by the following considerations : 



" Istly, An anterior dorsal vertebra (in Dr. Mantell's cabinet) 

 from the same deposits, with similar but less marked devia- 

 tions in the form of the articular facets, and with a configura- 

 tion of the neural arch, so far as it is perfect, identical with 

 that existing in more posterior dorsal vertebrae with plano- 

 concave joints, well-recognized as belonging to this great 

 herbivorous reptile, links together these apparently discrepant 

 vertebral types. 



2ndly, The amount of variation here assumed is parallel to 

 that which exists in its affine among the Crocodilidae, the 

 Steneosaurus rostro-minor 3 ; and similar changes in the form 

 of corresponding articular facets occur in the spinal column of 

 the Ruminants, Solipeds, and other Pachyderms ; 



3rdly, Other alterations in the sculpturing of the neural 

 arch of equal value with the modifications in the form of the 

 articular aspects of the body, are concomitant with these 

 changes in the different vertebrae just mentioned, and are 

 equalled in kind and degree by those which occur in the 

 series of neural arches of the spine in the recent Crocodiles ; 



4thly, These convexo-concave cervical vertebrae are found 



1 "Brit. Assoc. Reports," 1841, p. 92. 



2 "Philos. Trans." 1849. 



3 Vide Cuvier, " Oss. Fossiles," vol. ix. 8vo. edit. 



