HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 285 
tubercule of the rib by a very faint depression. This depression grows deeper as 
we follow it in the succeeding vertebre. The outer fourths of the posterior arti- 
culating surface of the centrum (the upper margins of the posterior articulating 
faces for the heads of the ribs) are still more strongly bent upward than in the 
fifth dorsal, and are widened antero-posteriorly, 
so as to form a deep groove for the exit of the 
nerve from the spine, composing about three- 
fourths of the circumference of the intervertebral 
foramen in specimens 1604 and 1713. In speci- 
mens 1714 and 1715 this feature is not so strongly 
marked. The anterior and posterior faces of the 
centra are practically vertical. The prezyga- 
pophyses look upward and very slightly forward; 
the postzygapophyses look downward, slightly 
backward, and very slightly inward. The faces 
for the tubercle of the rib are suboval or nearly 
circular, and look outward and slightly down- 
ward. As has been noted in the case of the pre- 
ceding vertebre, there is a very shallow keel-like 
Fie. 50. Sixth dorsal of M. elatus (No. 
projection on the under side, formed by an ante- 1604). x3. 
rior and posterior projection of the cartilaginous 
epiphysis, which are shown in specimen No. 1714 to have been received into shallow 
grooves or notches on the lower side of the centrum in the early life of the animal. 
These features are largely obliterated in the older and larger specimens, where a 
complete ossification has taken place. The distance between the articulating 
faces for the head of the ribs begins to increase in the sixth dorsal. In the pre- 
ceding vertebra they are very close to each other. The anterior face in this vertebra 
at its upper margin is thrown forward, being borne in its upper half upon a short 
pedicel, the superior margin of which assists in forming the lower margin of the 
intervertebral foramen. 
MEASUREMENTS OF SrxtH DorsAL VERTEBRA.” 
1604, AB, Tile, Sa, 
mm. mm. mm. mm. 
Greatest height from base of centrum to top of spine.............. 260 242 197 196 
Greatest transverse diameter measured across transverse processes. . 140 121 117133 103 
Greatest antero-posterior diameter measured from front of pre- 
zygapophyses to back of postzygapophyses.................. 77 68 68 56 
*8 Numbers in italics denote approximate dimensions, the specimen being broken or restored. 
