274 
DR. MANTEL L ON THE OSTEOLOGY OF 
tation of these vertebrse in my subsequent geological works*, yet I could not divest 
myself of the idea that this inference might be erroneous, from the fact that all the 
convexo-concave vertebrse of the Wealden were cervical ; it was indeed this circum- 
stance, and the extreme rarity of this type, which deterred the Rev. W. D. Conybeare 
and myself, at the very commencement of my exploration of the Wealden, from 
assigning them to the Iguanodon-f-. 
The inspection of a large anterior dorsal vertebra of the convexo-concave system, 
recently obtained by me from the Isle of Wight (Plate XXVIII. fig. 5), first suggested 
to Dr. Melville the idea that this bone, as well as the cervicals above described, 
belonged to the Iguanodon ; and he has spared neither time nor trouble to determine 
the correctness of this solution of the problem. To him, therefore, alone is due the 
credit of having first correctly interpreted the characters of this important part of 
the skeleton, should future discoveries confirm our present view of the subject. 
The gradual transition from the anteriorly convex cervical vertebrae with their 
deep posterior concavity (see Plate XXVIII. fig. 4® and fig. 4*), to the plano-concave 
vertebrse of the posterior dorsal and lumbar regions, appears, at least in the absence 
of the only certain evidence — a naturally connected spinal column — to warrant the 
conclusion that all these vertebral elements are referable to the same gigantic herbi- 
vorous Saurian:}:. If this opinion be correct, the adult Iguanodon must have ap- 
proached in the structure of its vertebral column, as well as in its maxillary and 
dental organs and hinder extremities, to that of the Rhinoceros and other large 
pachyderms ; for in them the convexo-concave type characterizes the cervical and 
anterior dorsal regions of the spine 
Anterior dorsal vertebra, Plate XXVIII. fig. 5. — In this specimen from Sandown Bay, 
the convexity is relatively less than in the cervical, and appears to indicate a gradual 
transition to the flat or but slightly elevated face of the middle dorsal, as shown in 
the fine vertebra found at Brook Bay with some enormous bones of the extremities 
of an Iguanodon; see Plate XXIX. fig. Si]. 
* Medals of Creation, p. 725. Wonders of Geology, 6th edit. p. 414. 
t See Geology of the South-East of England, p. 307. 
I A reference to Cuvier’s Oss. Foss., tome v. p. 156, will show that even in the typical form of the genus 
Streptospondylus the same disappearance of the convexo-concave character in the middle and posterior dorsals, 
takes place. 
^ If the discrepancy in the relative proportions and configuration of the cervical, dorsal, and caudal vertebrEe 
be regarded as presenting objections to this view, let it he remembered that in the spinal column of our domestic 
Mammalia an equal dissimilarity prevails ; for example in the Ox, in which the cervical are convexo-concave, 
and the convexity gradually disappears in the posterior regions of the spine ; and the bodies of the distal caudal, 
instead of being solid throughout as in the anterior vertebrse, have a large medullary cavity in the centre, as in 
the fossil reptile, called Poikilopleuron. 
II In my memoir of 1841, a fragment of a vertebra, which Baron Cuvier supposed to be part of the atlas of 
an Iguanodon, is described as such ; and the cast of the spinal canal in calcareous spar is regarded as that of the 
medulla oblongata (Philosophical Transactions, Plate IX. fig. 1). This specimen has since been cleared of the 
sandstone with which it was partially invested, and proves to be the neural arch of a crocodilian cervical vertebra. 
