126 REPORT — 1841. 



distinguished in different rogions of the spinal column. Hitherto I have not 

 met with any specimen of a cervical vertebra ; the comparatively small frac- 

 tured vertebra, Nos. gl^r ^"^ 2%%' " ^^i^ of the Iguanodoti" Mantell. 

 Catal., is an ordinary, or more posterior, cervical vertebra of a large Croco- 

 dilian Reptile, which, if not belonging to the Poikilopleuron, indicates a spe- 

 cies distinguishable from all other known Saurians*. The large cervical ver- 

 tebrte with ball-and-socket articular surfaces, agreeing with the Iguanodon 

 in size, have been shown to have these surfaces the reverse in position to 

 those in the Iguanag and modern Saurians, and to belong to the genus Strep- 

 tospondylus. The desirable knowledge, therefore, of the anatomy of that 

 region of the spine in the Iguanodon, which in other Saurians is usually 

 distinguished by its well-marked and varied characters, remains to be ac- 

 quired. 



Costal or dorsal vertebr(B\ . — Towards the middle or anterior part of this re- 

 gion tlie bodies of the vertebree are laterally compressed, and meet below at 

 an obtuse ridge. Through, apparently, a considerable proportion of the dor- 

 sal region of the spine, the neurapophyses rise vertically to a height equal to 

 that of the centrum, and expand into a broad and strong platform, the upper 

 surface of which is slightly concave transversely, and ai'ched from behind 

 downwards and forwards in a regular curve ; this platform is supported by a 

 strong vertical buttress on each side, and sends upwards from the whole of 

 its middle line a thick, broad and high spinous process. Two oblique, flat, 

 articular processes look downwards and outwards from the posterior angles 

 of the platform; and the corresponding anterior oblique processes, having 

 their flat articular surfaces looking upwards and inwards, and inclining to 

 each other at a right angle, terminate the contracted anterior part of the plat- 

 form, and do not project beyond it as two distinct processes separated by a 

 median fissure. They are not continued beyond the anterior end of the body 

 of the vertebrae, and consequently the posterior processes overhang the hinder 



* A portion of this vertebra is alluded to at p. 137, and figured at pi. ix., fig. 1, of Dr. Man- 

 tell's Memoir on the Iguanodon, pubhshed in the Philosophical Transactions for the present 

 year, 1841, as the " atlas of a young Iguanodon ;" its position iu the neck has been apparently 

 determined by the resemblance of the cast of calcareous spar, which fills up the spinal canal, 

 to the medulla oblongata. This resemblance arises from the expansion of the open ends of 

 the canal ; in which expansions, in the recent Crocodile, the contained spinal chord does not, 

 however, in the least degi-ee participate. The longitudinal fissure in the cast is due to a cor- 

 responding ridge of bone projecting from the inner surface of the contiguous wall of the spinal 

 canal ; doubtless giving attachment to the dura mater of the chord, but not impressing the 

 chord itself. The external surface of the vertebra exhibits an upper and a lower transverse 

 process for the attachment of a bilobed cervical rib, which unequivocally demonstrates it not 

 to agree with the Lacertian type of structure. 



t In the Memoir in the Philosophical Transactions, 1841, above quoted, Dr. Mantell says, 

 " The usual characters of the dorsal and caudal vertebra; of the Iguanodon have been pointed 

 out in my former works," and refers to the ' Fossils of Tilgate Forest,' and the ' Geology of 

 the South-east of England,' p. 136. I have again, therefore, carefully perused the passages 

 in which the structure of the vertebrae from the Wealden strata is alluded to in those valu- 

 able works, in the hope that the present tedious section of my Report might be cancelled ; 

 but they leave the same doubt, which their first perusal occasioned, as to whether the author 

 intended to attribute to the vertebra; of the Iguanodon the characters of those of the second 

 system of Wealden vertebrae, viz. Cetiosauriis ; or those of the fourth system, viz. Strepto- 

 spondylus. See Geology of the South-east of England, p. 306. M. H. v. Meyer adopts the 

 former, or the Cetiosaurian ijpe, for his characters of the Iguanodon's vertebrfe, from the 

 works to which Dr. Mantell refers. The six caudal vertebrae of the Iguanodon described in 

 the Memoir of 1841, are referred to, in the ' Geology of the South-east of England,' at the 

 conclusion of the account of the Hylceosaurus, and the accomphshed author there states, " The 

 bodies of these vertebraj, like those of the newly-discovered reptile, are shghtly concave at 

 both extremities," which is one of the characters whereby they might l)e distinguished from 

 the vertebra; of the Cefiosaurus. 



