HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. Di 
A comparison of the four specimens which have been mentioned in the pre- 
ceding paragraph makes possible an exact description of the bone. 
The neural spine is elevated, slender, and slightly recurved. This backward 
curvature is most noticeable in specimens 1703B and 1718, which are referred to 
M. peterson. The antero-posterior diameter of the spine at the tip is much less 
than at its origin, this being especially noticeable in specimen No. 1712, in which 
the neural spine is fully twice as deep at its origin as at its extremity. The pre- 
zygapophyses are elevated and oblique for articulation with the last cervical. 
In specimen No. 170388 the articulating surface of the prezygapophyses is rotund; 
in the others the surface is more or less oval. The prezygapophyses are much 
further apart than the postzygapophyses, and look upward, inward and forward; 
while the postzygapophyses look downward and outward. ‘The pedicels of the 
first dorsal stand mostly on the anterior half of the centrum and their transverse 
diameter is nearly twice that of their antero-posterior diameter at the middle. The 
neural canal is semi-circular in outline below, but above, owing to the depression of 
the lamine, it is pointed, as shown in Fig. 44, 4. The diameter of the centrum is 
greater transversely than vertically. Its anterior articulating surface, which is 
well preserved in specimens Nos. 1712, 1718, and 1719, looks forward and downward. 
It is somewhat cordate in outline. On the lower side of the centrum at the middle 
is a triangular process of the bone the base of which clasps the posterior margin of 
the anterior epiphysis, and the apex of which is produced backward as a slightly 
elevated keel. On either side on the centrum, just behind the anterior epiphysis, 
is a circular digital depression for the accommodation for the capitulum of the first 
rib. Immediately in advance of each of these depressions on each side is a deep 
pit, at the bottom of which is a small nutrient foramen. The outer extremity of 
the transverse process is strongly tubercular and deeply excavated, furnishing a 
broad concave articulating surface for the accommodation of the tuberculum 
of the first rib. This surface looks downward and forward. 
The posterior articulating surface of the centrum, as has already been stated, 
is in all of the specimens more or less mutilated through the loss of the epiphysis, 
but undoubtedly, in addition to a concave depression in the center to accommodate 
the anterior articulating surface of the succeeding vertebra, there was on either 
side a facet to accommodate the anterior surface of the capitulum of the second 
rib. The centrum in cross-section at the middle is subtriangular in outline. 
