WEALDEN FORMATIONS. 37 



references, measures nearly 3 feet in length ; its circumference at the middle of the shaft is 

 18 inches ; the contour of the rounded inward-projecting part of head, a, is \1\ inches ; 

 two flat longitudinal facets meet near the middle of the anterior surface of the shaft at a 

 rough and slightly elevated angle, c, which runs straight down to within thirteen inches of 

 the distal end ; the ridge there inclines towards the internal condyle and subsides. Two 

 strong muscles, answering apparently to the vastus internus and vastus externus, are indi- 

 cated by the surfaces converging to this ridge. The head of the bone is carried 

 inwards, overhanging the shaft. The line of the inner side of the shaft describes a 

 graceful sinuous curve, being first concave, then slightly convex at the middle, where 

 there is a peculiar process or ridge sometimes called the " third trochanter," d, but 

 which does not answer to the part so called, and projecting from the outer side of the 

 femur, in the Rhinoceros and some other mammalia. The part answering to the great 

 trochanter, b, is characterised by its compression in the direction of the bone from a to 

 I, and its great breadth in the opposite direction : it is flattened externally and is 

 divided by a deep and narrow fissure from the neck of the femur. The line of the 

 outer side of the shaft is slightly concave as it descends from the great trochanter, is then 

 convex along the middle part of the shaft, and is again concave as it is continued into 

 the somewhat expanded external condyle, e . This condyle is narrow in the direction 

 from e to /, fig. 1, especially at its prominent fore part, which has been broken off 

 in the specimen figured : it gradually expands towards its back part, and the femur of 

 the Iguanodon is characterised by the depth, as compared with the breadth, of the 

 rotular, (fig. lb, r') and popliteal, fig. lb, p, channels or cavities which separate the 

 outer condyle from the inner one /. The inner border of the femur below the process 

 d gradually inclines and expands to a flattened antero-posteriorly extended, slightly 

 concave surface, which then descends vertically to the articular surface of the condyle, 

 which surface extends horizontally at nearly a right angle with the line of the shaft 

 of the bone. The antero-posterior extent of the flattened inner condyle is 8 inches. 

 The thickness of the compact external wall of the shaft varies from half an inch to an 

 inch and a half. The medullary cavity, at its widest part, has an area of four inches by 

 two inches in diameter. Both ends of this fine bone are somewat crushed and mutilated. 

 The characters of the articular extremities of the femur which are obscured by the 

 mutilated condition of the large specimen above described, are beautifully shown in the 

 femur of a young Iguanodon, in the private collection of Mr. Holmes, obtained from a pit 

 near Rusper, four miles north of Horsham. The rounded portion of the head extends in- 

 wards ; it is indented at its anterior part by the commencement of a longitudinal broad 

 channel, which extends down upon the shaft ; the articular surface is not confined to the 

 inwardly produced head, but extends over the whole proximal horizontal surface of the 

 femur, expanding as it approaches the outer part of the head. The articular surface is cir- 

 cumscribed by a well-defined linear groove, which separates it from the longitudinal 

 striated surface of the shaft of the bone. At the posterior and external angle of the articular 



