436 



MEMOIRS OF THE CARNEGIE MUSEUM. 



also the ventral keel. The arterial canal is indicated by a deep groove on the 

 anterior border of the pedicel, which is often found completely bridged over by a 



Fig. 17. Diceratherium cooki Peterson. No. 18.53, Coll. Carnegie Museum. Ventral and anterior views 



of atlas. X h 



thin splint of bone. Additional features of this bone are well shown in the illus- 

 trations. (See Fig. 18.) 



The third, fourth, and fifth cervicals are, as usual, very uniform in their details 



Fig. is. Diceratherium cooki Peterson. No. 1853, Coll. Carnegie Museum. Lateral anil posterior 



views of axis. X i- 



of structure. There is, however, no neural spine on the third; the fourth has a spine 

 more or less clearly indicated ; the fifth a spine of considerable size varying in length 

 in different individuals. 



The sixth cervical is characterized by the broad, thin, hatchet-shaped, inferior 

 lamella of the transverse process, which sometimes terminates in a rounded process 



