CERATOPSIAN DINOSAURS FROjNI MONTANA GILMORE 



pared with the incomplete tibia of Leptoceratojys gracilis, except for 

 its smaller size, the bones are in full accord. 



The fibula is relatively slender with an expanded proximal end, 

 especially the anterior border, which strongly overhangs the shaft. 

 On the inner side of the upper fourth the fibula is longitudinally 

 hollowed out. The distal end is slightly widened transversely and 

 articulates closely with the calcaneum. The 

 shaft is flattened, with a strong torque in the 

 distal third of the shaft, which throws the 

 greatest diameters of the ends at right angles 

 to one another. 



The astragalus is proportionately larger 

 than in Triceratops and articulates with two- 

 thirds of the distal end of the tibia (fig. 6). 

 Wlien articulated it shows considerably less 

 from a posterior view than in Leptoceratops 

 gracilis; otherwise they are in full accord. 



The calcaneum when articulated is applied 

 entirely to the anterior side of the tibia and is 

 hardly visible from a posterior view of this 

 bone. Its superior surface is cupped and re- 

 ceives the distal end of the fibula. Its outer 

 surface is deeply excavated; anteriorly it pro- 

 jects forward prominently beyond the astragu- 

 lus and presents a broadly convex articular 

 surface dorsoventrally. Its inner side abuts 

 the astragalus. 



There are two ossified bones in the distal row 

 of the tarsus. These were slightly displaced 

 in the matrix so that their exact relationship 

 to the metatarsals is somewhat uncertain. The 

 outer one (fig. 7) was not far removed from 

 the end of metatarsal IV, and the presence of 

 a cupped upper articular surface for the cal- 

 caneum and a smooth hemispherical distal sur- 

 face for articulation with the cupped articular 

 end of metatarsal IV indicate its proper posi- 

 tion in the tarsus. Viewed from above this 

 bone is quadrangular, and it is thought that 

 its longer diameter is anteroposterior in the articular foot. In this 

 position, which puts the thickened end in front, it m.akes its most 

 perfect articulation with metatarsal IV and with the calcaneum. 

 The other tarsal is a fllattened quadrangular bone, which may have 

 articulated with metatarsals II and III. I find no clue as to its exact 

 position. 



ca 



Figure 6. — Right tibia, fi- 

 bula, astragalus, and 

 calcaneums of Leptocera- 

 tops sp. (U.S.N.M. No. 

 13863) : Anterior view. 

 as, Astragulus ; ca, cal- 

 caneum ; fi, fibula ; ti, 

 tibia. One-half natural 

 size. 



