ROOM III. DORSAL VERTEBRAE OF THE IGUANODOX. 265 



the neural arch is identical ; and the only essential difference 

 between the bodies of the respective vertebrae is, that the an- 

 terior articulating facet is less convex in the young reptile 

 than in the adult ; but as the posterior articular end of the 

 centrum is deeply concave, it is probable that in the recent 

 state the anterior facet possessed a cartilaginous convex 

 epiphysis, by which the ball-and-socket joint was completed : 

 as in the skeleton of the young Gavialihe facets of the sacro- 

 coccygeal vertebra are flat, though very convex in the adult ; 

 (ante. p. 167.) so in the Iguanodon, the ball and socket of the 

 cervicals may not have been fully developed and ossified till 

 the reptile arrived at maturity. 



The detached neural arch of a small cervical vertebra on 

 the shelf on the extreme left of Wall-case C, merits notice, 

 because I submitted it to the examination of Baron Cuvier 

 in 1830, who expressed his belief that it was the axis of a young 

 Iguanodon. The bone was then imbedded in a block of 

 Tilgate grit, and the cast of the spinal canal in calcareous 

 spar was visible, resembling the prolongation of the medulla 

 oblongata : the surrounding stone has since been removed, 

 and the fossil proves to be the neural arch of a cervical ver- 

 tebra probably, of a crocodilian reptile. 



DORSAL VERTEBRAE. Wall-case C, lowest compartment. As 

 the anterior dorsal vertebrae have not been found in juxtaposi- 

 tion with other known parts of the skeleton, our knowledge of 

 this region of the spinal column is scarcely more definite than 

 that of the cervical. A large convexo-concave anterior dorsal 

 in my possession, is figured and described by Dr. Melville 

 ("Philos. Trans.," 1849, p. 284, PL XXVIII.) as a vertebra of 

 the Iguanodon; and if that accurate observer's reference of the 

 cervicals proves to be correct, there can be no doubt that the 

 dorsal in question belongs to a reptile of the same genus. 

 Although there are no vertebrae of this type in the Museum, 

 yet the following notes may be useful to the anatomical 

 inquirer : 



" The anterior convexity is much less than in the cervical, 

 and the posterior concavity shallower ; the section of the 

 body would present a deep triangular outline, with the apex 

 below, corresponding to a thick median crest. The body is 

 contracted in the centre, so that the sides are concave 

 parallel to its axis, but convex vertically, owing to the great 



