HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 281 
Vertical diameter of posterior face for head of ribs...................-..004. 80 25 32 
Antero-posterior diameter of face for tubercle of rib......................... 28 26 26 
Transverse diameter of face for tubercle of rib..................-...------- 22 a 18 
Mransverse diameter of pedicels Wee eee ees sa noe eee ee 40 32 30 
Antero-posterior diameter of pedicel................0 cece cece eects 35 28 32 
Distance between faces for head of ribs..............0 20 cess eect eee 5 2 2 
Height of spine from neural canal to extremity................2---.002--05 240 180 226 
Antero-posterior diameter of spine above neural canal....................... 43 30 45 
AMtErO-posterior, diameter, Ofspineat tOpe sa. . 72-6. 2b eee eee oe 48 22 35 
Fourth Dorsal Vertebra. 
Four specimens of the fourth dorsal vertebra were recovered in the Agate 
Spring Quarries, Nos. 1604, 1703B, 1712, and 1715 (Carn. Mus. Cat. Vert. Foss.). 
No. 1604 lacks the upper end of the spine, and has sustained some injury at the 
extremity of the transverse processes. Nos. 1703B (see Fig. 49) and 1712 (see 
Fig. 45, 4) are practically perfect. No.1715 
has lost the extremity of the left transverse 
process, and is a little water-worn; other- 
wise it is in good conditoon. 
The spine of the fourth dorsal is slightly 
longer than the third (see Fig. 43). In 
horizontal section at its origin it is equi- 
laterally triangular. The transverse proc- 
esses are smaller than in the preceding 
vertebra, and are the first to show the 
tendency to develop a metapophysis, which 
becomes gradually more marked as we 
go backward along the vertebre. The 
superior margin of the centrum above the 
posterior articular faces for the heads of F1c.49. Fourth dorsal of Moropus petersoni (No. 
the ribs projects a little upward, assisting 1703B). Xz. 1, lateral view; 2, posterior view. 
thus in forming a portion of the wall of the lateral exits for the nerves of the spine. 
The prezygapophyses look forward and outward, and are subtriangular. The 
postzygapophyses look obliquely downward and a little inward and are antero- 
posteriorly oblong. Both the pre- and postzygapophyses are relatively smaller 
than in the preceding vertebra. The articulating surface for the tubercle is situ- 
ated at the outer extremity of the transverse process and forms the surface of a 
very short oval or circular lateral projection which is separated from the body of 
