174 THE MAMMALIA OF THE DEEP RIVER BEDS. 



expands to form the atlanteal surface ; behind this it contracts, to expand again 

 slightly towards the posterior end ; the hinder face is concave and there is a strongly 

 marked hypapophysial keel. The articular surface for the atlas does not rise quite 

 so high upon the sides of the neural canal as in Cervus ; its inferior border is more 

 curved and the median notch more deeply cut. The neural canal is lower and broader 

 anteriorly, posteriorly its opening is notably small; the pedicels of the neural arch 

 are perforated for the second pair of spinal nerves, but the foramina are smaller than 

 in Cervus ', in its anterior portion the neural arch is thin and plate-like, but gradually 

 thickens until, at the level of the postzygapophyses, it becomes massive and dip- 

 loe'tic. The spine is so broken that its shape cannot be determined, but it appears 

 to have been thicker and heavier than in Cervus elaphus. The transverse processes 

 are also broken away, but it can be seen that they were slender and probably short. 

 The odontoid process is completely spout-shaped but has a somewhat greater vertical 

 thickness than in the smaller species of Cervus. The postzygapophyses are small 

 and present outward as well as downward. As compared with the axis of Antilo- 

 capra, that of Blastomeryx is of almost the same antero-posterior length, but the 

 surface for articulation with the atlas is wider, the median contraction less pro- 

 nounced and the whole centrum more massive ; the base of the spine is also thicker. 

 But these differences are slight ; in general, the axis is very much the same in the 

 two forms. 



The third and fourth cervical vertebra3 are likewise of very similar construction 

 to those of the prong-buck; the centra are of almost exactly the same length as in 

 that animal, but the neural arches are somewhat shorter, and thus the gaps between 

 the successive arches are larger; the arches are also distinctly wider transversely. 

 The zygapophyses project more beyond the pedicels of the arch. The neural spines 

 are very low, though better developed than in A:ntilocapra ; on the third vertebra the 

 spine is anteriorly a single ridge, which projects beyond the front of the neural arch 

 and behind bifurcates into two ridges, one running to each of the postzygapophyses. 

 On the fourth the posterior ridges are low, but the anterior rises into a distinct but 

 very short spine. On the corresponding vertebrae of the prong-horn these ridges are 

 indicated only in the feeblest way. 



Measurements. 



B. ANTILOPINUS. A. AMERICANA. 



M. M. 



Length of centrum of axis 062 .064 



Width of anterior face of axis 048 .044 



Third cervical, length of centrum 050 .052 



Fourth cervical, length of centrum 054 .051 



