148 Baron F. Nopcsa — British Dinosaurs — 



knees sometimes for more than 90 degrees, while as shaped in the fossil 

 the tibia would become dislocated if forced to make an angle of 

 more than 45 degrees with the femur. This tends to show that the 

 cartilage on the distal end of the femur must have been at least 4 cm. 

 thick, and this is certainly not too much when we consider that the 

 distal femoral cartilage of the macerated Gallus figured above had 

 a thickness of 45 mm., while the femur itself measured 94 mm. in 

 length. It becomes evident that just as we could never try to bring 

 the macerated femur of Gallus into correct juxtaposition to the 

 acetabulum without allowing for a great amount of cartilage, so we 

 cannot base any conclusion as to the position or direction of the femur 

 in Stegosaurus exclusively on the shape of its articular surface ; and this 

 must be emphasized all the more since such an attempt has recently 

 been made bj Tornier in regard to the similarly-shaped femur of 

 Diplodocus. The reason why the discussion of the femoral cartilage 

 caps of Omosaurus needs to be so detailed is, that Tornier has recently 

 expressed the belief that the similarly-shaped femur of Diplodocus was 

 only covered with a few millimetres of cartilage. 



Even by those who hold the contrary view the amount of cartilage 

 in Diplodocus is thought to be correlated with the aquatic habits of 

 this monster, but this theorj^ cannot apply to the heavily armoured 

 Stegosaurs. I quite believe that the feeble ossification of the sternal 

 apparatus and the low degree of ossification of the distal carpals and 

 tarsals in most Dinosaurs are much more likely to explain the great 

 cartilage caps on the femora of the Stegosauridas and similar animals 

 than the hypothetical aquatic habits. These features and the coarse 

 structure of the bones indicate a low degree of ossification in the whole 

 body, and the great masses of cartilage were probably needed to ensure 

 the continuous increase of size throughout life. Perhaps this was one 

 of the causes for the rapid extinction of the Sauropoda. 



Besides the development of the so-called articular surfaces, the feeble 

 development of the fourth trochanter is an interesting feature in the 

 femur of our new Stegosaurus. According to Marsh's description the 

 femur of the American Stegosaurus shows no marked fourth trochanter, 

 while St. durobrtiensis bears this process. The femur of the type- 

 specimen of 0. armatus is too badly crushed to show this feature ; on 

 0. vetustus, according to F. von Huene, there is no such process. 

 0. Lennieri shows a rounded but marked swelling with a rugose 

 surface that can well be called a distinct fourth trochanter, and 

 St. prisons bears on the interior posterior surface, rather high up on 

 the shaft of the bone, an obtuse swelling, which dies out very rapidly 

 both upwards and downwards, and must be considered as the last 

 trace of this trochanter. It may be concluded that the variable 

 development of the fourth trochanter affords a good character for 

 distinguishing the different species of Omosaurs and Stegosaurs. 



The tibia and fibula (Fig. 7) are represented by more than half of 

 each bone in St. prisms. Like in the Ceratopsidse and St. tingulatus, 

 the strong tibia is distally enlarged and flattened on the antero- 

 exterior border for the reception of the fibula. Both bones are so 

 closely applied against each other and to the fused calcaneum and 

 astragalus that this part of the foot formed one inflexible piece. 



