74 DINOCERATA. 



The Third Vertebra. (Plate XXII, figures 1-5.) 



The third cervical of Dinoceras mirahUe (number 1036) is shown in 

 Plate XXII, figures 1-5. This vertebra, in the type specimen, is not in a 

 good state of preservation, but represents fairly the main characters of the 

 third cervical in this genus. 



The pre-zygapopliyses are somewhat concave, to fit the convex 

 post-zygapophyses of the axis. The neural canal is large, and the arch 

 above it is only moderately developed, and without a spine. The lateral, 

 or vertebrarterial, foramen is oval in outline, and is protected by a strong- 

 transverse process. The uiuler surface of the centrum is marked by a 

 median kmgitudinal keel, as shown in figin-es 3 and 5. 



The third cervical vertebra of D'moccras mirahik (number 1255) is 

 short, and the articular faces of the centrum are both somewhat concave. 

 The anterior face is slightly less excavated than the posterior. The length 

 of the centrum is less than its vertical diameter, and the latter is greater 

 than the transverse diameter. The epiphyses are incompletely ossified, 

 and only imperfectly united to the centrum. These general characters 

 apply also to the remaining cervical vertebrae 



The principal dimensions of the third vertebra in one specimen of 



Dinoceras are as follows : 



Measurements of Third Cervical Vertebra. {Dinoceras mirabile, No. 1255.) 



m. 



Length of floor of neural canal (approximate), . . - .055 



Length of centrum, along under surface, — -058 



Vertical diameter of posterior epiphysis, 078 



Autero-posterior extent of zygapophyses, . _ . . _ - -092 



Diameter of lateral foramen (approximate), .020 



The Fourth Vertebra. (Woodcuts S7 and SS, below.) 

 The fourth cervical, vertebra in Dinoceras resembles, in its main 

 characters, the one last described. The pre-zygapophyses are nearly flat. 

 The neural canal is somewhat smaller. The process to protect the lateral 

 foramen is more sti-ongly developed, and the under surface of the centrum 

 is without a distinctly marked keel. 



