WEALDEN FORMATIONS. 5 



most freely moveable cervical vertebrae, and, a fortiori, therefore, between the less 

 moveable dorsal, lumbar, and caudal vertebrae, is further indicated by the interval 

 separating the centrums in the three cervical vertebrae preserved with the natural co- 

 adaptation of their zygapophyses, and with their natural upward curvature, in the 

 specimen figured in Tab. I. The elasticity of the concentric ligamentous substance 

 has permitted the vertebral bodies, in this upward flexure, to be more divaricated at 

 their lower than at their upper borders. 



Nothing in the characters of these unequivocal vertebrae of the Iguanodon affords 

 any countenance to the conjecture that the broad and sub-depressed convexo-concave, 

 or streptospondylian vertebrae, which I had stated might be a cervical modification of 

 the vertebral column of the Cetiosaur, are from the cervical region of the Iguanodon. 

 The parapophysis of the true cervical vertebrae of this reptile, figs. 2 and 4, p, is 

 developed, in a great proportion from the centrum, in a less proportion from the 

 neurapophysis, close to the anterior articular end of the centrum, which surface is 

 continued upon the parapophysis. This process is short, obtuse, and terminates by a 

 surface for the attachment of the head of the rib. 



The neurapophyses, which are confluent at their summit, remain free below, where 

 they are joined by suture to the centrum, embracing the upper third of the articular 

 end. They contribute, as above stated, a small proportion to the parapophysis ; ascend 

 a short way vertically with a smooth and concave outer surface, then develope large 

 zygapophyses, and, from the outside of the anterior of these, z , send out a diapophysis, 

 d, for articulation with the tubercle of the rib. The neural arch is notched before, and 

 more deeply behind ; there is a ridge above each zygapophysis, and these ridges con- 

 verge to the base of the neural spine. The broad, flat articular surface of the anterior 

 zygapophysis, z , looks inwards and a little upwards and backwards ; that of the poste- 

 rior zygapophysis, s ', exhibits, of course, the opposite aspects ; the outer border of both 

 zygapophyses is rounded. The zygapophyses are not connected, externally, by a ridge 

 continued forwards and backwards from the diapophysis, as in the dorsal vertebrae, 

 where such ridges form the neural platform, Tab. XXXV, n, ri. The neural canal is 

 proportionally wider than in the dorsal vertebra of the older Iguanodon (' Monogr. Creta- 

 ceous Reptiles,' Tab. XXXVI), but this is no doubt due to both the comparative im- 

 maturity of the present specimen, and to the more advanced region of the spine, 

 formed by the vertebrae under consideration. 



The bases of the neurapophyses do not extend so far inwards as in the dorsal 

 vertebrae, but leave a median tract of the floor of the neural canal which is formed by the 

 centrum itself: this part of the centrum sinks into a hollow, and is perforated by the 

 myelonal veins. 



The antero-posterior extent of the base of the neural spine is two lines, that of the 

 neurapophysis, between the extremes of the anterior and posterior zygapophyses, being 

 thirteen lines : the spine is much compressed laterally : it has been broken off near its 



