30 FOSSIL REPTILIA OF THE 



with very fine, subparallel, short impressions ; tliese grow deeper and more irregular 

 at the thick, rugged, and everted margins of the articular ends. 



The neurapophyses are firmly anchylosed here, as in the caudal region, and the 

 line of the primitive suture is hardly discernible : their base is shorter than the short 

 centrum, and is attached nearer its anterior part ; in the Iguanodon the neural arch 

 is very nearly coextensive in antero-posterior diameter with the centrum supporting 

 it ; in a dorsal vertebra of an Iguanodon 4g inches in breadth, the antero-posterior 

 extent of the base of the neural arch is 4 inches ; in the present vertebra, which exceeds 

 7 inches in breadth, the antero-posterior extent of the neural arch is 2| inches, and 

 only 2 inches a little above the base. The outer side of the neurapophysis is convex 

 in the axis of the vertebra, and concave in the opposite direction as it ascends to the 

 base of the diapophysis, showing only the posterior of those ridges and hollows that so 

 singularly characterise the same part in the dorsal vertebrse of Streptospondylus 

 Cuvieri. The antero-posterior diameter of the base of the diapophysis is 2 inches, its 

 vertical diameter 1 inch. The diameter of the neural canal (n) is 1 inch 9 lines. The 

 articular surfaces of the anterior zygapophyses (Tab. IX, fig. 1 , z) are flat, and look 

 upward and slightly inward and forward. In the Iguanodon, their under margins, in the 

 dorsal vertebrae, converge at nearly a right angle ; in the present vertebra they incline to 

 each other at an angle of 40°. The spinous process begins to rise immediately behind 

 the anterior zygapophyses by a narrow vertical plate, which seems as if it were nipped in 

 between two shallow depressions ; its base ascends obliquelv, and grows thicker to the 

 posterior part of the neural arch. The summit was not entire in any of these vertebrae. 



The height of this dorsal vertebra to the posterior origin of the spinous process is 

 9^ inches ; from the base of tlie neurapophysis to the upper part of the transverse 

 process, measures 3 inches. 



No. irVtV in the Mantellian Collection, British Museum {" Vertebra of Iguanodon, 

 8 inches in diametfer," MS. Catalogue), may have actually presented that dimension 

 when entire, for even now, not allowing for the margin of the posterior articular 

 surface which has been broken away, it measures 7 inches across the surface. This 

 remarkable specimen, which may probably have afforded the type of the " third or 

 plano-concave" vertebral system, in the summary of the vertebral characters of the 

 Wealden reptiles given by Dr. Mantell in his 'Geology of the South-east of England,'* 

 and which accords best with the characters assigned by M. H. von Meyer to the 

 vertebrse of the Iguanodon,f presents, in fact, in a striking degree, those of tbe 

 vertebrae of the Cetiosaurus, and belongs to a more posterior part of the dorsal region, 

 perhaps to the loins, of the same individual, certainly to one of the same species, as 

 the vertebra (No. 2133) last described. A figure of a corresponding vertebra bisected 

 vertically is given in Tab. IX, fig. 2. 



* 8vo, 1833, p. 292, fig. 3. f ' Palseologica,' p. 212. 



