48 FOSSIL REPTILIA OF THE 



the same degree and direction of curvature as that on the right side ; but the left groove 

 becomes shallower and wider towards its beginning, which may be traced as far back 

 as the base of the phalanx, as in Mr. Saull's specimen. The vascular foramina, at 

 and beyond the opposite termination of the left groove, are not less numerous and 

 conspicuous than are those on the right side; but the left groove is somewhat in 

 advance of the right, and sinks into the unsymmetrical phalanx one inch and four lines 

 from the broken apex. At one fourth of an inch below the left vascular groove there 

 is a shallow, smooth impression, /, fig. 1, along the distal half of the bone, indicating 

 the extent to which the lateral margin of the claw reached on that side : there is no 

 corresponding impression on the opposite side, which coincides with the dissymmetry 

 of the phalanx, in showing it to have belonged either to an outermost toe of the left 

 foot, or to an innermost toe of the right foot. 



The exterior of the bone around its base is sculptured, as in other and normally 

 shaped phalanges, by smaller but coarse longitudinal impressions, corresponding with 

 the attachments and insertions of the articular capsule and ligaments. The part of the 

 bone, proved by the direction of the large smooth lateral grooves to be the under side, 

 is the shortest, and is most convex transversely. The upper side is the longest, and 

 is narrower across than the under side. 



In. Lines. 

 The length of this phalanx is . . .46 (doubtless 5 in. when entire.) 



The longest diameter of its base is . .33 



The shortest diameter of its base is . .22 



The distance between the distal terminations of the 



lateral grooves . . . .10* 



What might be the chances, it may be asked, that the single small bone supporting 

 the median frontal horn should be found fossil, on the hypothesis that the Iguanodon 

 possessed, like the Iguana cornuta, such a dermal appendage ? Supposing an extreme 

 toe, outermost, or innermost, of the fore and hind feet of the great reptile to have had 

 a claw shorter and straighter than the rest, it would be four to one that the bone of 

 such claw should be found, than the unique bone of the horn. By great good luck, 

 indeed, the latter might once turn up; but one could not expect the only bone of its 

 kind, and one of the smallest in the skeleton of the Iguanodon, to be frequently found. 

 Yet I have had not less than three " horns of the Iguanodon" submitted to my 

 inspection since describing the one so called in the British Museum. And two of 

 these supplemental examples of straight conical claw-phalanges are figured in 

 Tab. XVII. The first, figs. 3 and 4, was discovered in the Wealden of the Isle of 



* The two figures in Tab. XVII have been made with the most scrupulous accuracy from the original 

 fossil now in the British Museum, and exhibit characters not before given in any published figure of the 

 so-called "horn of the Iguanodon." 



