312 BRITISH FOSSIL REPTILES. 



proximal end of the bone, a longitudinal column, the top of which may be compared to a 

 trochanter, is separated by a deep and narrow vertical groove or fissure, from the main 

 shaft of the bone, and falls into that shaf a little lower down : here the shaft expands 

 and becomes rather flattened from before backwards, but is sub-quadrangular : a low 

 ridge, produced by the union of two broad and flat surfaces, extends down the middle 

 of the anterior surface of the shaft, and, inclining towards the inner condyle, gradually 

 disappears. A little below the middle of the shaft the inner margin is produced into 

 the angular ridge or low and long process, above described {d, fig. 1). The shaft of 

 the bone has a large medullary cavity. The distal end is characterised by a deep and 

 narrow anterior longitudinal groove, situated not quite in the middle, but nearer the 

 external condyle ; there is a corresponding deep longitudinal groove on the posterior 

 part of the distal end, which is wider than the anterior one, and in the middle of the 

 bone, separating the two condyles, but inclining beneath, and as it were undermining 

 the backward projecting part of the internal condyle ; this is much more prominent 

 than the external one, which is traversed or divided by a narrow longitudinal fissure. 

 The articular surface is irregular and tuberculate. 



The following are some of the dimensions of this femur : 



The lateral diameter of proximal end 



The lateral diameter of distal end . 



Antero-posterior diameter of outer part of proximal end 



Antero-posterior diameter of outer part of internal condyle 



In. Lin. 



2 8 



3 

 2 

 2 3 



In five separate long bones, in the Mantellian Collection, having the general 

 characters of the two bones above described and of those of the Maidstone Iguanodon, 

 which are marked " femur" in PI. 2, ' Binosauria,' Section II, ' Cretaceous Reptiles/ 

 Nos. 1 and 3 difi'er from Nos. 4 and 5 in the greater inward production of the head, 

 making the concavity of the line descending from the head to the median internal 

 ridge somewhat deeper. The lower angle of this median ridge is more produced 

 in Nos. 1, 2 and 3, than in Nos. 4 and 5. The whole inner contour is more regalarly con- 

 cave in No. 5 than in Nos. 1 or 3. Of these five bones. No. 2 was found associated with 

 a tibia and fibula ; and the differences above indicated illustrate the extent of the indi- 

 vidual varieties of the same bone, so far as my opportunities of comparison have extended. 



The femur of the Iguana differs as widely from that of the Iguanodon as does that 

 of the Monitor or any other Lacertian reptile. The forms of the head and trochanter 

 of the femur of the Iguana are just the reverse of those in the Iguatiodon. The head 

 of the femur in the Iguana is flattened from side to side, and its upper convex surface 

 is extended from before backwards, making no projection over the gentle concave line 

 leading from its inner surface down to the inner condyle. In the Iguanodon the head 

 is rounded and rather compressed from before backwards, and is produced, as in 

 Mammals, over the inner side of the shaft. 



