

ROOM III. DORSAL VERTEBRA OF THE IGUANODON. 267 



ridge, which passes outwards from beneath, and is gradually 

 blended with the process. The spinal canal is nearly circular, 

 and expands slightly in front, where it assumes a transversely 

 oval outline. The following are the dimensions of the ver- 

 tebra above described : 



Antero-posterior length of the body 5 inches. 



Transverse diameter of anterior face 5 



Vertical diameter of the same 6 



Height from the base of the centrum to the neural plat- 

 form 7 n 



Height of the spinous process 7 



Width of spinal canal anteriorly \\ 



The essential distinctive characters of the dorsal vertebrae 

 of the Iguanodon, as demonstrated by Professor Owen 

 (" Brit. Reports," p. 127), are the strong, broad, and lofty 

 bony platform into which the neural arch expands, with its 

 supporting buttresses ; and the presence of a lower transverse 

 process (parapophysis) for the reception of the head of the 

 rib, either on the side of the centrum, as in the anterior 

 dorsal vertebrae, or from the side of the neural arch, as in 

 the middle dorsal; characters which distinguish these ver- 

 tebrae from those of ophidians, lacertians, and enalosaurians ; 

 while the absence of the posterior convex facet on the cen- 

 trum, separates them from those of the existing species of 

 crocodilians and lizards. 



The usual condition in which dorsal vertebrae are found, 

 is the centrum or body deprived of its neural arch, as in 

 Lign. 35, fig. 8 (ante, p. 164) ; specimens with the upper trans- 

 verse processes (diapophysis of Professor Owen), and the 

 neural arch (as in fig. 6, which is either a posterior dorsal 

 or lumbar), are comparatively rare ; a few vertebrae only 

 have been obtained with the spinous process entire. In the 

 Maidstone specimen, (ante p. 146, Plan p. 138, Case No. 23) 

 there is a series of dorsal vertebrae (some are probably lum- 

 bar), but these are so much distorted by compression, that 

 not one presents the normal form, either of the body or the 

 apophyses. 



The great strength and expansion of the transverse pro- 

 cesses of the posterior dorsals indicate the large development 

 of the abdominal region in this stupendous reptilian vegetable 

 feeder. 



RIBS. Wall-case C, lowermost compartment. There are 



