WEALDEN DINOSAURS. 375 



As the fully developed toes which follow this rudiment have respectively three, 

 four, and five phalanges, the analogy of both the fore- and hind-foot of the Iguanas 

 and Monitors would indicate the small innermost metapodial (Pis. 43 and 44, i) to be 

 the rudiment of the first toe (pollex or hallux), and the three fully developed toes to be 

 the homologues of the second, third, and fourth toes of the feet in the Lizard tribe ; the 

 fifth toe being wholly suppressed in the Iguanodon. The analogy of the Crocodilian 

 foot would lead to the same conclusion, since the second toe in that reptile has three 

 phalanges, and the third toe has four phalanges, whilst in the hind-foot the fifth toe is 

 suppressed. The fourth toe, however, in some of the Crocodllia differs from that in the 

 Lacertilia, in having only four phalanges, and usually wanting a claw. Hence it would 

 seem that, whilst the Iguanodon resembled the Crocodilia, as regards the hind-foot in 

 that order, in the suppression of the fifth toe, it resembled the Lacertilia in having the 

 fourth toe unguiculate, and with five phalanges : but it differs from both those Rep- 

 tilian orders in the suppression of the first toe, and its representation by a hidden 

 rudimental metatarsal, thus reducing the number of conspicuous and functional toes 

 to " three." 



The resemblance to the hind-foot of the Crocodilia in the suppression of the fifth 

 toe, and the resemblance of the third and fourth toes, in regard to their nearly equal 

 length, to those toes in the Monitor, render it most probable that the tridactyle foot 

 of the Iguanodon, here described, is a "hind-foot;" but it cannot be assumed that 

 the fore-foot may not have been similarly modified. 



In the leading characteristics of the bony framework of the foot, whether fore or 

 hind, it is interesting to find that the Iguanodon manifests a combination of Croco- 

 dilian and Lacertian characters, with superinduced Dinosaurian peculiarities, analogous 

 to the plan of structure which I have had occasion to point out in other parts 

 of its fossilized remains. So far as the Dinosaurian peculiarity of a reduced number 

 of functional toes prevails, that order departs further from the general Reptilian type 

 than do the existing Crocodiles and Lizards. 



Having premised these general I'emarks on the fossils in question, I proceed next 

 to point out the chief characters of the constituent bones of the foot. 



The rudimental metapodial of the first or innermost toe (Pis. 43 and 44, i ) articu- 

 lates by its proximal end with a notch, 9 lines in diameter, at the middle of the inner 

 (tibial) surface of the second metapodial ( n). It seems not to have been anchylosed 

 at this part, from the circumstance that the slender bone has been broken, 

 soon after death or interment, and the upper portion has been displaced obliquely 

 from the lower half, which maintains, perhaps through anchylosis, its natural position ; 

 the displaced portion is cemented in that position by the hardened matrix to the con- 

 tiguous large metapodial.* The rudimental metapodial, 9 lines by 6 lines in the 



* In the f]gure it is represented as restored to its natural position. 



