WEALDEN FORMATIONS. 39 



In the Iguana the trochanter is compressed from before backwards, and is 

 separated by a wide and shallow groove from the oppositely compressed head ; in the 

 Iguanodon the trochanter is singularly flattened from side to side, and is applied to the 

 outer side of the thick neck, from which it is separated by a deep and narrow fissure. 

 The Iguana has no sub-median internal process, and its distal condyles are slightly 

 divided by a shallow depression. 



The circumference of the femur of the Iguanodon very nearly equals one half its 

 length ; the circumference of the femur of the Iguana only equals one fourth its length ; 

 yet the femur of the Iguanodon equals the united length of eleven of its dorsal 

 vertebrae, while that of the Iguana equals the united length of only six of its dorsal 

 vertebrae. 



The femora of the Iguana stand out, like those of most other Lacertians, at right 

 angles with the vertical plane of the trunk, which is rather slung upon than supported 

 by those bones ; but it is evident from the superior relative length and strength of 

 those bones in the Iguanodon, from the different conformation of the articular, especially 

 the proximal extremities, and from the ridges and processes indicative of the powerful 

 muscles inserted into the bone, that it must have sustained the weight of the body in a 

 manner more nearly resembling that in the pachydermal Mammalia. As in some of the 

 more bulky of these quadrupeds, the indication of the " ligamentum teres" is wanting 

 in the head of the femur of the Iguanodon. 



Tibia and Fibula of the Iguanodon. Tab. XV, figs. 2 — 7. One fourth the nat. size. 



By the side of the femur, figured in Tab. XV, fig. 1, were found two other bones, 

 the largest of which corresponds with the tibia in recent Crocodiles and Liza 

 The homologous bone, better preserved, of a somewhat larger individual, is figured in PI. 

 XV, fig. 2. The external part of the head of this bone is produced horizontally, audits 

 back part expands and divides into two condyles, e , f, fig. 2 ; the circumfej ence of the 

 proximal articular surface is 30 inches. The longitudinally finely striated vertical 

 surface of the shaft of the tibia commences at the anterior part of the proximal end 

 along a well defined curved line, which runs transversely across the bone, convex 

 downwards in the" middle, and concave downwards at each end: the bone gradually 

 contracts, and assumes, about 8 inches below the head, the sub-quadrilateral form ; it 

 is broadest from side to side; its circumference is here 15 inches. The anterior 

 surface is flattened ; the outer side is convex or rounded ; the dense external walls 

 of this bone are very thick, at least 1 inch. The proximal articulation is convex from 

 behind forwards, but, at the middle, it is slightly concave from side to side. 



In. Lin. 

 Its lateral diameter is . . . . . 12 



Its antero-posterior diameter is . . . . 13 6 



