8 MEMOIRS OF THE CARNEGIE MUSEUM 
backward from the diapophysis nearly to the posterior border of the centrum. 
There are deep and well-defined post-, pre-, supra- and infradiapophysial cavities. 
The Fifteenth ? or last Cervical (Plate I., Fig. C 15).— This vertebra differs from 
the one preceding it in being a little shorter and with more widely expanded neu- 
ral spine and cervical ribs. The pleurocentral cavity is less extended posteriorly 
than in the preceding cervical and its bottom is interrupted by an oblique and an 
intersecting lamina. There is a shallow infracentral cavity on either side of the 
mec..in line on the inferior surface near the anterior end of the centrum. There is 
a single infraprezygapophysial cavity. The neural spine is absolutely simple as in 
the preceding cervical. The postzygapophyses are higher and the posterior branch 
of the horizontal lamina consequently more nearly vertical than in the preceding 
vertebra. The anterior branch of the horizontal lamina has the margin somewhat 
expanded as shown in Plate I., Fig. C 15, indicating that this vertebra gave some 
support to the scapula. 
The First Dorsal (Plate I., Fig. 1). — Fortunately as has already been stated this 
vertebra and the two preceding were still closely interlocked by their zygapophyses 
when discovered in the quarry. They were taken up in a single block of the enclos- 
ing sandstone and were received at the musenm still occupying their original posi- 
tions relative to one another. In consideration of these facts there can be no ques- 
tion regarding the exact position of these three vertebree in the vertebral column. 
That the vertebra now under consideration was a dorsal is conclusively shown not 
by the presence of tubercular and capitular rib facets showing that it supported on 
either side a free rib, for there are in our collections of sauropods, skeletons of other 
dinosaurs fully adult but, with the posterior cervical, bearing free cervical ribs 
articulating by both tubercular and capitular facets as do the ribs of the dorsal re- 
gion. ‘The character in this vertebra distinguishing it as a dorsal is the broadly ex- 
panded external border of the anterior branch of the horizontal lamina. This ele- 
ment has been thus modified in this and the succeeding dorsal, no doubt, as is 
known to be the case in Diplodocus to give greater surface for the attachment of the 
powerful muscles necessary for the support of the scapula. That this was the first 
and not the similarly modified second dorsal is conclusively demonstrated by the 
fact that it was found interlocked by its zygapophyses with the last cervical. 
This vertebra is essentially complete, although the form of the centrum has been 
considerably altered by crushing. In the accompanying drawings this distortion 
has been eliminated as much as possible. The length of the centrum is noticeably 
less than that of the last cervical and the antero-posterior diameter of the pleuro- 
central cavity is greatly shortened. The floor of this cavity is interrupted by neither 
