82 



BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 





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before rne, although it appears to be absent in S. ungulatus (fig. 46) and the allied 

 European forms. The presence of this atrophied trochanter, which is such a 

 prominent feature of all bipedal dinosaurian femora, apparently represents the 

 remnant of a much larger process, which has been handed 

 down from a bipedal ancestry. 



"With the exception of having the trochanter just described, 

 the whole proximal end of the femur of Stegosaurus is remark- 

 ably like those of the Sauropodous dinosaurs, especiallr that of 

 Diplodocus. 



Marsh ' has pointed out the absence of the third tro- 

 chanter (now recognized as the fourth) in S. ungulatus and I 

 find it absent in S. stenops. The origin of the caudo-femoral 

 muscle is nevertheless usually indicated by an obtuse longi- 

 tudinal swelling, which fades out rapidly both above and be- 

 low. As shown by Nopcsa in S. p?iscus "it must be considered 

 as the last trace of this trochanter." In specimen No. 7380, of 

 which we have both femora preserved, the vestigal fourth 

 trochanter is roughly rugose. In the American Stegosaurus the 

 fourth trochanter appesirs always to be more vestigal than in 

 Tnceratops. 



The distal end of the femora is more expanded trans- 

 versely than antero-posteriorly. The external condyle, as usual. 

 is larger than the internal. The intercondylar notch is wide 

 and moderately shallow. The external condyle has on its 

 outer side a shallow groove which probably transmitted one 

 of the strong tendons. 



Nopcsa 2 has contributed some interesting observations 

 on the Stegosaurus hind hmb, which are given herewith: 



I wish to emphasize the fact that in this genus [Stegosaurus] the amount 

 of cartilage on both ends of the femur was decidedly much greater than in 

 the Ornithopodidae, and that the shape of the proximal and distal end of the 

 bone must have been originally somewhat different from the present shape. 

 The lack of a trochlea on the distal end of the femur of Stegosaurus can 

 give us a clue to the amount of cartilage missing, for Stegosaurus, being a 

 terrestrial animal, can not have walked, and especially sat down without 

 bending its knees sometimes for more than 90°, while as shaped in the 

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

 than 45° 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 4.5 mm., while the femur itself measured 94 mm. in length. It becomes evi- 

 dent 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 can not base any conclusion 

 as to the position or direction of the femur in Stegosaurus exclusively on the shape of its articular sur- 

 face. * * * 



Even by those who hold the contrary view of the amount of cartilage in Diplodocus it is thought 

 to be correlated with the aquatic habits of this monster, but this theory can not apply to the heavily 



Fig. 46. — Left femur of 

 Stegosaurus ungulatus 

 Marsh. ^ nat. size. 

 Front view, c, inner 

 condyle; s, shaft show- 

 ing ABSENCE OF FOURTH 



trochanter; (, great 

 trochanter. after 

 Marsh. 



1 Dinosaurs or North America, 1S96, p. 191. 



* Gcol. Mag., vol. S, No. 4, 1911, pp. 147-148. 



