OSTEOLOGY OF CARNIVOROUS DINOSAURS. 



69 



Tyrannosaurus and Gorgosawus is nearer the top and has a stronger development 

 posteriorly. The lesser trochanter is a wide transversely compressed blade, that is 

 separated on its inner side from the head by a wide cleft (a, figs. 1, 2, 4, and 5, pi. 14). 

 The relatively larger size and more proximal extension of this trochanter will serve 

 to distinguish the femur of Ardrodemus from its contempory Ceratosaurus, as is 

 indicated by a comparison of figure 64 with plate 14. Viewed from above (fig. 5, 

 pi. 14) the articular portion of the head is roughly rectangular in outline, the greatest 

 diameter being transverse. This articular- surface is comparatively smooth, gently 

 rounded antero-posteriorly and extends downward on both anterior and posterior 

 aspects more especially the latter. The distal end has the usual condylar develop- 

 ment, the two condyles being separated by a deep intercondylar groove (fig. 7, pi. 14). 

 The anterior intercondylar groove is relatively narrow and extends at some distance 

 up on the anterior surface of the shaft. On the inner anterior side of this aspect of 

 the femur is an oblong oval depression having a roughened surface representing the 

 point of attachment of the femoro-tibialis muscle. External to the outer condyle 

 is the usual guidon groove, though this shelf appears to be relatively wider than 

 found in the Predentate dinosauria. 



Measurements of femora of Antrodemus valens Leidy. 



Tibia {t.) — Both tibiae are present with specimen No. 4734, U.S.N.M. The 

 left, having been found articulated with the fibula, astragalus, and calcaneum, was 

 selected for illustration and description here. 



As in Ceratosaurus, the tibia is shorter than the femur. It has expanded 

 ends distally, in a transverse direction, and proximally in a fore and aft direction. 

 In lateral aspect the shaft is straight, though the upper third is inclined forward on 

 the anterior side. The shaft is flattened on the front side, but the remaining sur- 

 faces are evenly rounded. 



Viewed proximally the outline is roughly triangidar, the apex being directed 

 anteriorly (A. fig. 48). On the posterior face are two relatively small overhanging 

 condyles, separated by a comparatively shallow and narrow intercondylar groove. 

 An especially large and prominent process extends forward and upward from the 

 inner half of the front face (fig. 48). It rises above the level of the articular surface 

 of the proximal end, and extends forward with a curve outward, thus greatly in- 

 creasing the antero-posterior diameter of this end of the bone. The outer side of 

 this process is concave, the inner convex, the convexity being continued on around 

 the inner side of the end. 



Below the process described above, the antero-external border is a very large 

 cnemial process, which is directed outward and slightly forward. This process is 

 144035°— 20 6 



