HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 297 
the upper margin of the centrum. They look upward and strongly forward. In 
the other two specimens the prezygapophyses look upward, forward, and outward, 
but are widely separated from the upper margin of the centrum. The postzyga- 
pophyses look backward, downward, and slightly inward, and are advanced back- 
ward, being supported by a backward projection from the radix, forming a pedicel 
for these faces. The transverse process becomes trituberculate, the upper portion 
immediately in advance of the postzygapophyses extends transversely forward 
as an elevated ridge of bone, from which about half-way between the postzyga- 
Fig. 58. Thirteenth dorsal of M. ela- Fig. 59. Thirteenth dorsal of M. petersoni (No. 17 
fus (No. 1604). Xz. 03C). +. 1, lateral view; 2, posterior view. 
pophyses and the articulating face for the tuberculum of the rib a well-defined 
metapophysis rises, pointing outward and forward. Between this metapophysial 
projection and the face for the tuberculum of the rib is a somewhat conical process, 
which projects backward, outward, and upward. The intervertebral foramen is 
formed by a deep groove running outwardly between the transverse process and 
the posterior articulating surface for the head of the rib, the upper margin of which 
closely approaches a spinous projection extending backward from the posterior 
surface of the radix so as almost to enclose the groove. The articular faces 
for the heads of the ribs are widely separated, the one in front being small and 
tending to coalesce with the face for the tubercle of the rib and that behind being 
fully three times as large as that in front. 
