of the Iguanodon in the Isle of Wight and Isle of Portland. 427 



As large bones of the Megalosaurus are found mixt with those of the 

 Iguanodon in the Wealden formation, and some doubt may arise, from this 

 circumstance, as to the possibility of our large metacarpal being derived from 

 the foot of a Saurian of this genus, I have engraved on the same plate, with 

 my metacarpal bone of an Iguanodon, the metatarsal bone of a Megalosaurus, 

 thirteen inches long (Plate XLI. fig. 5 and 6), and a metatarsal bone of a 

 crocodile (Plate XLI. fig, 7 and 8), both from the oolitic slate of Stonesfield, 

 and now placed in the Oxford Museum. The elongated form and slender 

 proportions of both these bones differ most essentially from the short and 

 thick characters which mark the metatarsus of the Iguanodon. This variation 

 is in due conformity with the difference in the habits of the respective ani- 

 mals ; the lighter and more slender structures being more suited to the feet 

 of the carnivorous reptiles, while the more massive and ponderous form was 

 equally adapted to the bulk and babits of a reptile which was herbivorous. 



Together with our metacarpal bone, there were found at Sandown Bay 

 some vertebrae and fragments of other bones of smaller reptiles ; and in the 

 same place also about four years ago, the Rev. Gerard Smith discovered part 

 of a very large bone, probably a fragment of a coracoid bone, or of the pelvis, 



joint than that assigned to it, excepting in the little toe of the right foot, or little finger of the right 

 hand ; both these are places for which the flatness of its posterior surface, as well as its vast size, 

 would render it unfit. 



Srdly. It cannot be a carpal bone analogous to either of the two carpal bones of the crocodile, 

 (Cuvier's Oss. Foss. vol. v. Part II, Plate IV, fig. 13, c, d,) because both articulating surfaces of 

 these two carpal bones are concave, whereas the anterior surface of our fossil bone is highly con- 

 vex and nearly semicircular, and must have formed part of a hinge having very considerable 

 power of flexure, such as it may have afforded if it were a metacarpal bone, articulating with the 

 first phalangeal bone of the left thumb. 



■ithly. The posterior surface of our fossil accords with the metacarpal place thus assigned to it ; 

 Its slight degree of concavity would not admit of sufficient flexure for a phalangeal bone, but 

 enough of motion for the articulation of a metacarpal with a carpal bone : see Plate XLI. fig, 3. 

 profile of posterior surface of fig, 2, 



5thly, The nearly straight edge by which the posterior surface is bounded towards the left 

 side (Plate XLI, fig, 4, h, c, where it is drawn reversed,) accords with the supposed juxtaposi- 

 tion of this edge of the metacarpal of a left thumb to that of the straight edge of the metacarpal 

 of a fore finger of the left hand, Tlie circular form of the right portion of the margin could be 

 found only in a bone which came in contact with no other bone on the side so curved outwards, i. e. 

 only in a metacarpal of the left thumb, or a metatarsal of a right little toe. The strong markings 

 produced by the origin and insertion of muscles, tendons, and ligaments, which appear at the points 

 a, h, c, d, in figs. 1 and 2, would probably be sufficient in the hands of an experienced anatomist 

 to decide with certainty by reference to the muscles to which they had relation, whether the bone 

 formed part of a little finger or little toe of the right side, or is derived from a thumb or great 

 toe of the left side. 



