HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. DNS, 
diameter of each condylar articular surface is greater than its transverse diameter, 
and they become narrower below. They are vertically and horizontally very deeply 
concave, forming a cup-like cavity for the reception of the condyles. 
The posterior articulating surfaces are in all the smaller specimens subrotund, 
but in the larger specimens, owing to the increasing width of the atlas, without a 
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Fic. 20. Inferior view in outline of atlas of Mo- 
Fie. 19. Superior view in outline of atlas of Mo- 
(C. M. Cat. No. 1604.) 
ropus elatus Marsh. +4. (C. M. Cat. No. 1604.) ropus elatus Marsh. 4. 
corresponding relative increase in the vertical diameter, these surfaces tend to 
become more or less oval in outline. They are convex horizontally and vertically 
and look inwardly. 
The articulating surface for the odontoid process of the axis is somewhat 
triangular in outline, with its external boundaries poorly defined in all specimens. 
The margins of all the other articulating surfaces both before and behind are well 
defined. 
The transverse processes of the atlas are broad and wing-like. 
margins in the smaller and younger specimens are thin, but in the larger and older 
specimens the margins become thickened at their anterior and posterior extremities. 
Their outer 
as 
we 
Fig. 22. Diagram representing contour of 
neural canal of axis of Moropus elatus in horizon- 
tal section. 
Fic. 21. Superior view of atlas of M. 
petersont (No. 1703A). X44. 
On the median line on the upper side of the superior arch there is in all speci- 
mens a slightly raised bony ridge, representing the dorsal spine. This is most 
conspicuous in specimens Nos. 1724, 1728, and 1729. 
