310 BRITISH FOSSIL REPTILES. 



length, and 13 inclies in circumference at the largest tarsal extremity. The colossal 

 proportions of a fragment of a femur in his possession, from Tilgate Forest (PI. 18, 

 fig. 1 of the same work), which measures 23 inches in circumference in the smallest 

 part, sufficiently accord with those of his metatarsal bone last mentioned, as well as 

 our metacarpal bone from the same formation in the Isle of Wight, and give strong 

 probability to the opinion that all these three fragments of the skeleton of a reptile of 

 such extraordinary stature may be referred to the Iguanodon. It is obvious that 

 these supposed metacarpal and metatarsal bones are much shorter and thicker in their 

 proportions than the metacarpal or metatarsal bones of any living lizards or crocodiles ; 

 but when we consider the enormous weiglit which the foot of an animal whose femur 

 was 23 inches in circumference must have sustained, a reduction of length and 

 increase of bulk in the bones which supported such a colossal frame, must have been 

 attended with many mechanical advantages." 



The distal or ungual phalanges of the Iguanodon, although doubtless offering 

 certain modifications of form in different toes, are shown by those preserved in the 

 Maidstone Iguanodon, and by others of much larger dimensions found associated with 

 the bones of the great Iguanodon of the Horsham quarry, to have had a less incurved, 

 broader, and more depressed form than in other known saurians. Two of the largest 

 ungual phalanges of the Horsham Iguanodon in Mr. Holmes's collection, are broad, 

 subdepressed, and exhibit, as in most other saurians, the curved vascular groove on each 

 side : they have an articular, slightly concave base, and terminate anteriorly in a round 

 blunt edge ; the outer boundary of the lateral grooves form at the posterior end of the 

 groove, a laterally projecting process, making this part of the phalanx broader than the 

 articular extremity or basis. The following are dimensions of the largest of the two 

 phalanges : 



In. Lines. 

 Length . . . . . . .54 



Breadth . . . . . ..32 



Breadtli at articular end . . . . .30 



Depth . . . . . ..23 



at the posterior end it gradually diminishes to the distal end. 



The phalanx is slightly bent downwards ; the under surface being concave longi- 

 tudinally, l)ut convex from side to side. The under surface is rough, the upper 

 surface nearly smooth, except at the margin of the articular surface, on the projecting 

 sides and at the distal extremity, which is sculptured by irregular vascular grooves 

 and holes. The phalanx has a slight oblique twist to one side, and is somewhat 

 thinned off to that side on which the curved groove is longer than on the other side. 



In Mr. SauU's museum is an ungual phalanx of an Iguanodon, wdiich nearly 

 equals those from Horsham, and presents the same subdepressed form. The base is 

 slightly convex transversely, more concave vertically ; the articular surface is 



