84 



BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



Tibia (t. ) . — In Stegosaurus stenops, the tibia is very much shorter than the femur, 

 the ratio being as 1 : 1.68. 



The tibia of Stegosaurus may at once be distinguished by the unusual angula- 

 tion of the expanded ends; that is, the greatest diameter of these extremities 

 lies in about the same plane, while in the Ceratopsia and Camptosauridse these 

 diameters occupy planes nearly at right angles to one another. Articulating 

 the proximal end of the tibia with the femur as in Camptosaurus , Triceratops, or 

 Trachodon tends to throw the articulated foot out at right angles to the longer 

 axis of the body. This at once raises the question as to the correctness of the 

 interpretation of the articulation of the limb as shown by 

 various figures and illustrations. 



The proximal end shows on the posterior side two com- 

 paratively small condyles which overhang the posterior sur- 

 face of the tibia. The external border of this end is shallowly 

 concave antero-posteriorly for the reception of the proximal 

 end of the fibula. On the anterior side is a broadly rounded, 

 blunt enemial crest. The least diameter of the constricted 

 shaft is below the middle. The distal end is widely expanded 

 antero-posteriorly, but without marked expansion trans- 

 versely. On the anterior face of this end the surface is un- 

 equally divided by a broad, shallow, longitudinal groove, 

 which probably transmitted the tendons of the flexor muscles 

 of the foot. The smaller or external part represents, in func- 

 tion at least, the external malleous of the mammahan tibia. 

 It extends below the internal surface with which the as- 

 tragalus unites, and articulates on its inner side with that 

 bone. The anterior surface of this part is flattened and 

 articulates closely with the fibula (fig. 47) . 



The articular surface for the astragalus is cupped. This 

 surface is irregularly gouged out (fig. 48), into which fit cor- 

 responding projections on the proximal end of the astragalus. 

 This union renders the bones immovable upon one another and brings about a con- 

 dition favorable to their early coossification, as evidenced by the ankylosis of these 

 bones in four of the six tibia preserved in the National Museum collections. 

 A front view of the tibia is shown in figure 47. 



a~ 



Fig. 47. — Left tibia and fib- 

 ula of Stegosaurus un- 

 gulatus marsh, a nat. 

 size. Front view, a, as- 

 tragalus; c, calcaneum; 

 /, fibula; (, tibia. After 

 Marsh. 



Measurements of tibia. 





S. stenops, 



tvpe No. 



4934, right. 



5. ungu- 

 latus, No. 

 6646, right. 



Stegosaurus sp. 



No. 

 7379, left. 



No. 

 7380, right. 



No. 

 7387, right. 





771771. 



643 

 265 



mm. 

 696 

 275 

 245 

 9S 



mm. 

 602 

 230 

 217 

 87 



mm. 

 565 

 210 

 185 



77 



77170. 



570 



210 



232 



79 









So 





