452 J. W. HULKE ON" IGUANODOlir PEESTWICEII 



The Calcaneum (PL XX. figs. 3, 4), smaller than the astragalus, is- 

 (to borrow a simile from the older anatomists) a somewhat boat-shaped 

 bone, wider behind than in front. It has an upper, an under, and 

 an outer surface. The under surface is crescentic, strongly convex 

 from back to front, and less convex transversely. It forms an arc 

 of a circle, and was plainly part of a trochlear joint. The upper 

 surface is subdivided by a prominent ridge, directed obliquely from 

 behind forwards and inwards, into a posterior part, a deep trough 

 parallel with the ridge, and an anterior part somewhat quadrilateral 

 in shape, with the anterior corners rounded off, and the outer and 

 jposterior sides longer than the two others. The outer surface, 

 vertical, is non-articular; below, behind, and in front it is slightly 

 encroached on by the trochlear surface. Its lower border is an arc ; 

 its upper border is straight. Eather behind the middle this latter 

 is interrupted by the outer end of the ridge mentioned as sub- 

 dividing the upper surface. The inner border of the bone is thin 

 and crenated; here, as lately mentioned, the upper and under 

 surfaces nearly meet. 



When the calcaneum is placed with the border which I have 

 termed inner touching the outer border of the astragalus, and the' 

 upper or crural surfaces of the bones are viewed, it is evident that 

 the deep trough in the calcaneum behind the oblique ridge in its 

 upper surface forms the outward continuation of the trough in the 

 outer half of the upper surface of the astragalus, and that it arti- 

 culates with the outer tibial malleolus, which, as I have already 

 said, is not borne on the astragalus. The quadrilateral depression 

 in the upper surface of the calcaneum, lying in front of this tibial 

 trough and of the oblique ridge, received the lower end of the fibula, 

 the distal part of the shaft of which rests in a splint-like manner 

 on the front of the tibia parallel with its outer border. Yiewed 

 from beneath, the convex under surface of the calcaneum is seen to 

 complete the pulley, of which the astragalus forms much the larger 

 part. The mutual adaptation of the two bones is so suggestive, 

 that this alone would have justified the identification of the lesser- 

 bone with the OS calcis, a bone previously unrecognized ; but I for- 

 tunately obtained confirmation of the true skeletal position in a 

 hind foot of Hypsilophodon Foxii, a closely allied form, in which I 

 found the bones in situ joined to each other, as also to the tibia and 

 fibula, in the manner described *. 



In the articulation of its tibia with the calcaneum, as well as 

 with the astragalus, the Iguanodon's foot difi'ers from the hind 

 foot in the three extant orders, Chelonia, Lacertilia, Crocodilia — in 

 each of which the distal end of the tibia rests wholly on the 

 astragalus, which latter, by an outer facet, is in contact with the 

 fibula. But in the very point wherein the Dinosaurian foot differs 

 from that of living reptiles, it closely resembles the foot of birds. 



* Since this was written, by the courtesy of M. E. Dupont, the Director, 

 I have had an opportunity of studying some of the very instructive Iguanodon- 

 remains lately acquired by the Museum of Natural History at Brussels, and' 

 have been gratified by finding the bones in natural articulation as described. 



