314 BRITISH FOSSIL REPTILES. 



The fibula nearly equals the length of the tibia ; the well-preserved specimen figured 

 in PI. 20, figs. 4 — 7, forms part of Mr. Holmes's" choice collection of Wealden Re- 

 mains from the vicinity of Horsham : it has belonged to a younger individual Iguanodon 

 than the femur and tibia figured in the same plate. 



The tibia of the Iguanodon equals the united length of nine of the dorsal vertebrae, 

 while in the Iguana it does not exceed the united length of five dorsal vertebrae, 

 although it more nearly equals the femur in length than in the Iguanodon. The head 

 of the tibia is more expanded and more complicated by the condyloid prominences, 

 and by their deep and wide groove in the Iguanodon than in the Iguana. 



The disparity of strength between the tibia and fibula is considerable, but the difiference 

 in the thickness of the lower extremities of the two bones is less than the proportions 

 of the shaft would indicate. On the middle of one of the flat sides of the fibula is an 

 oblong rough surface slightly raised, measuring 3 inches by 2 inches. The articular 

 extremities of the fibula are tuberculate, the lower and larger end is 5 inches across, 

 the smaller one 3 inches across. 



The fibula is more expanded towards the distal end and more flattened against the tibia 

 in the Iguanodon than in the Iguana. It differs, also, from that of the Iguana in the well- 

 marked, shallow, longitudinal concavity along the side of the lower half of the shaft which 

 is next the tibia, as is shown in PI. 20, fig. 4, (the views of the fibula in this plate have 

 unfortunately been drawn on the stone upside down). The opposite side of the shaft is 

 smooth and convex, as shown in fig. 3. In one diameter the fibula gradually contracts 

 from the proximal to the distal end, as is shown in fig. 5 ; but in the opposite 

 diameter it expands in a greater degree, and very suddenly, at the articular distal end. 

 The form of the proximal surface is shown at fig. 7, that of the distal one at fig. 6. 



The unusually perfect specimen, from which the figures 3-7 were taken, was obtained 

 from the Wealden formation at the Tower-hill pit or quarry, near Horsham, by my 

 esteemed friend G. B. Holmes, Esq., of that town, by whose accomplished daughter 

 the original drawings of the bone were made. Another fibula of a small Iguanodon 

 from a pit at Rusper, in the same gentleman's collection, equals the antero-posterior 

 extent of the spines of eight dorsal vertebrae of the same individual. This bone is 13 

 inches long, 6 lines across the proximal end, and two inches across the distal end. 



Metatarsal and Phalangeal Bones of the Iguanodon. Plates 21 and 22. Nat. size. 



Of the great Iguanodon from the Horsham quarry, two metacarpal or metatarsal 

 bones are preserved in natural juxtaposition, in Mr. Holmes's Museum : one exceeds 

 the other by four inches in length, and measures 2 feet 6 inches : the breadth of its 

 distal end is 3 inches 3 lines ; the shaft is compressed and subtrihedral ; its texture is 



