156 DINOCERATA. 



The surface of the navicular exposed upon the dorsal aspect of the 

 foot (Plate XLIX, fig-ure 7) is short vertically, more or less rounded 

 from side to side, and varies much in the degree of smoothness, or 

 tuberculation, in different specimens. 



I'he under, or plantar, surface, shown in figure 9, projects into a 

 large rounded tubercle, and is of considerably greater extent along the axis 

 of the foot than above. 



The outer surface (figure 10), presented to the cuboid, is more or less 

 covered b}" an articular face, extending along the proximal margin of tlie 

 bone, confluent with the astragalar face, and, in life, moving upon a 

 corresponding face upon the inner side of the cuboid. 



The proximal surface of the bone (figure 11) is mostly occupied bv a 

 large articular surface, for union witli the astragalus. This surface is 

 somewhat saddle-shaped, being distinctly concave transversely, but 

 somewhat convex from above downward. Below the articular face, the 

 bone usually extends into a strong plantar tubercle, which may, however, 

 (number 1218) be much less developed than in the specimen figured. 



None of the specimens present any indication, on the proximal face, 

 of a surface for articulation with the ealcaneum, such as is found on the 

 corresponding bone of the elephant. 



The distal surface of the navicular (figure 12) presents three articular 

 faces, one for each of the cuneiform bones. These faces are confluent 

 with each other, and the inner one, for the entocuneiform, may be small, 

 and indistinct. Usually, it Is of considerable size, and elongated from 

 above downward. It is oval in sha])e, moderately convex in Ixitli 

 directions, and oblique to the axis of the bone, looking some\\hat outward. 

 The median of the three faces is sub-quadrate in outline, a little broader 

 above than below, and confluent, on each side, Avith the adjacent faces. 

 This face is slightly concave from side to side, and from al)ove downward, 

 nearl}' flat. 



The face for the ectocuneiform is sub-quadrate, tapering below, concave 

 in both directions, or nearly flat from above downward. 



