256 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



A large bone of this kind from Tilgate Forest, which I 

 refer to the Iguanodon, approximates in many respects to 

 that of the Mosasaurus (ante, p. 196.) The body bears some 

 resemblance to that of a vertebra, but the large cells and 

 hollows which pervade it throughout readily distinguish it. 

 It forms a thick pillar or column, which is contracted in the 

 middle, and terminates at both extremities in an elliptical 

 and nearly flat surface. Two lateral processes pass off ob- 

 liquely, and are small in proportion to the size of the column. 

 On placing this fossil beside the homologous bone of the 

 Iguana, we at once perceive that the relative proportions of 

 these parts are reversed ; for in the latter the pillar is small 

 and the lateral processes large. 



From the great size of the body, and the extreme thinness 

 of its walls, the tympanic cells must have been very consi- 

 derable in number and magnitude, and have constituted a 

 large portion of the auditory cavities. This bone is 6 inches 

 high, and 5| inches in its greatest diameter. It is larger 

 than the tympanic bone of the Mosasaurus, and exceeds by 

 14 times in linear dimensions that of an Iguana, four feet 

 long. This specimen is figured on a reduced scale in the 

 " Geology of the S. E. of England," PL XI. fig. 5. 



SPINAL COLUMN OF THE IGUANODON. Wall-case C. (ante, 

 p. 138.) The bones composing the vertebral column are the 

 most important elements, and at the same time the most 

 numerous remains of the skeleton, that occur in the Wealden 

 deposits ; but, unfortunately, the structure of the neural arch 

 and its processes renders the characteristic parts of the ver- 

 tebrae so liable to injury, that it is but rarely the specimens 

 imbedded in the rocks are in a perfect state, or can be 

 extricated entire. For reasons previously mentioned, con- 

 nected portions of the skeleton are but seldom met with in 

 fluviatile deposits ; hence, but few examples of vertebrae in 

 juxtaposition have been obtained. Of the Iguanodon but 

 one specimen has been discovered, exhibiting the cervical, 

 dorsal, lumbar, and caudal, vertebrae of the same indi- 

 vidual. 



The difficulty of arriving at any satisfactory conclusions as 

 to the generic relations of the mutilated vertebrae which were 

 among the earliest indications of the Wealden reptiles at the 

 commencement of my researches, can scarcely be conceived 



