HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 301 
The Fifteenth Dorsal Vertebra. 
Five specimens of the fifteenth dorsal were recovered, No. 1604, No. 1703C, 
No. 1708, No. 1718, and No. 1715. In the fifteenth dorsal a profound modification 
takes place in order to adapt it to union with the succeeding lumbar series. The 
articulating surfaces of the postzygapophyses look outward and downward, are 
convex, and are supported upon the posterior surfaces of the laminz, which divide 
on either side of the neural arch and project far backward, overhanging the pos- 
terior articulating face of the centrum. The metapophysis is greatly lengthened, 
the transverse process projects strongly outward. There is but one articu- 
lating facet for the head of the rib on the anterior face of the centrum. The 
specimen No. 1604 is in almost perfect condition and together with the fragment 
of No. 1708, as will be pointed out later, presents very remarkable differences 
from the other three specimens. No. 1703C is also an almost perfect specimen, 
the extremity of the right metapophysis alone having been slightly injured and 
requiring minor repairs. No. 1708 consists of a large centrum with pre- and 
ECA 
CG 
\s \ h 
Fig. 62. Fifteenth dorsal of M. ela- Fig. 63. Fifteenth dorsal of M. petersoni (No. 1703C). 
tus (No. 1604). X43. <4. 1, lateral view; 2, posterior view. 
postzygapophyses and the neural arch crushed down upon the centrum. Specimen 
No. 1713 has.lost the right metapophysis and the outer extremity of the transverse 
process on the same side. The bone js slightly distorted, the distortion having 
apparently taken place during the life of the individual. The right postzyga- 
pophysis is lower than the left and has been crushed inwardly, showing that the 
individual to which it belonged had sustained spinal injuries. The posterior 
