72 DINOCERATA. 



The Axis. (Plate XXI.) 



The axis in Dinoceras mirahilc (number 1036) is robust, and 

 proportionally shorter than the corresponding vert3bi-a in the tapir. The 

 centrum is moderately flattened below, but not excavated as in the tapir, 

 and presents, medially, a tuberculation at the union of its centrum with 

 that of the first vertebra. The odontoid process is distinctly conical, and 

 not at all excavated above. Its perpendicular diameter, moreover, exceeds 

 its transverse. It is pointed in front, and bears, on its under surface, a 

 saddle-shaped articular face for union with the atlas. This surface is not 

 confluent with the lateral surfaces, as in the elephant, tapir, and most 

 Ungulates, but is perfectly distinct, as in the kangaroo, and in man. The 

 lateral articular faces are moderately convex in both directions, and have 

 their longest diameter neai'ly transverse. 



The neural arch is massive, and its lateral walls are not pierced by 

 foramina, agreeing, in that respect, with those of the kangaroo. On the 

 lateral surfaces of the centrum, the vertelirarterial, or lateral, foramen was 

 present, and circumscribed by bone. Its u[)per Avail was much weaker 

 than the lower, instend of subequal, as in the tapir. The neural arch is 

 surmounted by a short and stout neural spine, low in front, and rising 

 behind, though less rapidly than in tlie tapii-, and becoming rather 

 indistinctly bifid at the top. The neural spine is deeply excavated behind. 



The posterior zygapophyses are robust, slightly convex, and look 

 more downward than outward, and onh' sliglitlv liackward. Tlie 

 posterior face of the centrum is transvei-se, and broadly oval in outline. 

 The floor of the neural canal is flattened, and [)resents a number of 

 vascular foramina leading into tlie centrum. 



The transverse processes of this specimen are imperfectly preserved, 

 but were evidently pierced, above the middle, by a large lateral foramen. 

 The processes appear to have been directed rather less strongly backward 

 than in the tapir. 



The principal dimensions of the axis in three specimens of Dinoceras 

 are as follows : 



