OSTEOLOGY OF THE AKMOEED DINOSAUEIA. 117 



The external border continuing down from the proximal end is rugosely 

 roughened, and with the process here called the great trochanter was probably the 

 point of insertion of the gluteal muscles. It appears that with the retrogression 

 of this trochanter, which is vestigal in Stegosaurus, the point of insertation of these 

 muscles gradually changed, until, in S. ungulatus and in the Sauropod dinosaurs, 

 with the disappearances of this trochanter, the superior outer border functions as 

 the trochanter major, as first correctly determined by Osborn in Diplodocus. 



The shaft is slightly bowed from end to end, the arcuation of the center being 

 forward. The bone is flattened antero-posteriorly being wider than deep. 



The fourth trochanter is present, and placed above the middle on the postero- 

 internal border of the shaft, and although broken as mentioned above, appears to 

 have been more prominently developed than in Stegosaurus. 



The external condyle (see oc, fig. 69) as in other dinosaurs is larger than the 

 inner, both rounding up well on the back. They are separated by a wide but 

 shallow intercondylar notch. The internal condyle is weak and much compressed 

 transversely, and has on its internal side the usual longitudinal groove. 



Measurements of Femur No. Jfl5%. 



771771. 



Greatest length 495 



Greatest breadth proximal end 190 



Greatest breadth distal end 170 



Least width of shaft 65 



Dorsal vertebrae. — The dorsal region of the backbone is represented by a solitary 

 dorsal centrum, which is considerably distorted by pressure. Making due allowance 

 for distortion, the centrum would be deeper than wide, with flattened sides and 

 slightly expanded ends, having concave articular surfaces. Neural canal large; 

 pedicels of neural arch contracted antero-posteriorly as they rise from the centrum, 

 suggestive of a high neural process. The principal measurements of this centrum 

 are: Greatest length 74 mm.; greatest height 63 mm.; greatest transverse diam- 

 eter 50 mm. 



Caudal vertebrae. — Six caudal vertebrae were found with this specimen, but the 

 great size of three of these precludes the possibility of their pertaining to this indi- 

 vidual. This also renders the association of the remaining three somewhat prob- 

 lematical. 



The better preserved one from the median caudal region has a massive centrum 

 being as wide as long; articular ends slightly biconcave; chevron facets well devel- 

 oped on posterior end; diapophyses leave the centrum on a level with the neural 

 canal, the latter comparatively small, with greatest diameter transverse; spinous 

 process missing, though the fractured base indicates that it was thickened. 



This centrum has the following dimensions : Greatest length 80 mm. ; greatest 

 width 80 mm.; greatest height 65 mm. A caudal from the distal end of the tail 

 is relatively more elongated; without transverse process; centrum somewhat com- 

 pressed transversely; with biconcave ends. It has a length of 50 mm. 



Ribs. — The ribs, with the exception of the proximal portion shown in plate 

 27, are all fragmentary. Many of these fragments are triangular hi cross section. 

 From these pieces it would be inferred that none of the ribs were very massive. 

 51873°— Bull. 89—14 9 



