UNGULATA. 



and flattened astragalus extends from the navicular considerably 

 over the cuboid, while the fibula distinctly articulates both 

 with the astragalus and calcaneum. The two best-known 

 genera are Coryphodon and Dinoceras, from the Lower and 

 Middle Eocene respectively. 



Coryphodon (figs. 166168). The skull is elongated, with a much- 

 produced facial region, which is somewhat expanded towards the end of 

 the snout below the wide narial opening. The basicranial axis is straight. 

 There are no excrescences on the top of the skull, though rudiments 

 of these are sometimes feebly distinguishable. The zygomatic arch is 

 massive and expanded, while the jugal unites with the maxilla in front of 

 the orbit. The maxilla is also massive and usually deeply indented on 

 the side behind the canine. The nasal bones taper in front. The 



Coryph 

 left 



molar- premolar series of upper (A) and lower (u) jaws, 

 alf nat. size. L. Eocene (Wasatch Formation) ; Wyoming. 



(After Marsh.) 



cerebellum is proved to have been nearly or quite as large as the cerebral 

 hemispheres, and much expanded transversely. The dental formula is 



i. . , c. , pm. , m. The canines are comparatively large, especially 

 i. 3, c. 1, pm. 4, m. 3 



those of the xipper jaw, and there is a short diastema between the canine 

 and the premolars in both jaws. The lophodont character of the pre- 

 molars and molars is well shown in the drawing of the upper and lower 

 dental series, figs. 166 A, B. The neck is of considerable length and flexible, 

 and the odontoid process of the axis vertebra is a short peg. The length 

 of the slender tail is uncertain. No clavicle has been observed. The 

 distal end of the radius is larger than that of the ulna. The femur bears 

 a distinct third trochanter. When in a position of rest the femur and 

 tibia are slightly inclined to each other, and the fibula is clearly proved to 



