70 DINOCERATA. 



along the inner side. The median facet, for articulation with the odontoid 

 process, is flattened in front, or slightly convex in antero-posterior 

 direction, and extends longitudinally over the greater part of the inferior 

 arch of the atlas. Its boundaries are well marked on all sides, as are 

 also those of the lateral faces. Hence the articulation between the atlas 

 and axis admitted but little rotary motion to the head. 



The spine of the atlas is not well marked, although the superior arch 

 is massive, and its anterior surface is rough and tuberculated. This arch 

 is pierced on each side anteriorly by a foramen (figure 84, d ), the inner 

 opening of which is just above the inner and upper angle of the condylar 

 articular surface. Externally, this foramen is connected Ijy a more or less 

 evident groove with one piercing the transverse ])rocess lengthwise. This 

 groove runs vertically down the side of the atlas, and through a deep notch 

 in the anterior margin of the transverse process. In the tapir, this groove 

 passes through a foramen, instead of a notch in the anterior part of the 

 transverse process. A similar arrangement is seen in the horse, ox, sheep, 

 camel, and in various other Ungulates. 



The transverse processes of the atlas are short, and strong. They are 

 moderately flattened, thicker and stouter behind than before, and placed 

 obliquely, so as to slant strongly downward and backward. Anteriorly, 

 the outer margin runs rapidly down to the lateral arch of the atlas, but is 

 separated from it at the base of the process by the deep notch, mentioned 

 above. Posteriorly, they are thickened and rugose. The base of each 

 lateral process is perforated by a foramen, directed somewhat downward, 

 and forward. The under surface of the atlas (figure 86) is smooth and 

 even, with no rugosity to mark the median line. 



The atlas of Dinoceras mirabiJe is shown in Plate XX, and that of 

 Tinoceras grande, in the woodcuts below, figures 84, 85, and 80. The 

 position of the atlas, with reference to the skull, is represented in the 

 restorations in Plates LV and LVI. 



