MORPHOLOGY OF BAROSAURUS LENTUS. 13 
more than either XI or XII. The position of the diapophysis in D. camegiei, however, 
is neither constant nor progressive, being so extremely far forward only in cervicals 
XI, XII, and XIII. In D. camegiei it is the fourteenth cervical that has the longest 
centrum; in Barosauriis it is the twelfth. 
Cervical XIII (Vertebra Q) (PL II, Fig. 2). — This is a huge bone, with very 
broad, wing-like expansions which bear the prezygapophyses and extend backward to 
the diapophyses about three-eighths of the distance from the anterior end of the 
centrum. These wing-like expansions measure 530 mm. in length, the width over both 
being about 570 mm. The ventral aspect of the centrum resembles that of cervical XII, 
except that instead of one median ridge there are two slight ridges which, while widely 
apart at the posterior end, converge opposite the diapophyses. Posteriorly, these ridges 
become about 50 mm. deep, and bound laterally the ventral aspect of the bone. The 
sides of the centra are also crossed by buttress-like horizontal lamina; which serve to 
strengthen the diapophyses and are continued beyond them into the wing-like expansions 
above mentioned. The latter are supported from beneath by a number of bracket-like 
expansions of bone, which give the inferior aspect of these plates an appearance of 
considerable complexity. The prezygapophyses are also widely expanded, the entire 
structure being doubtless correlated with considerable lateral movement of the neck in 
the region of the posterior cervicals. 
The pleurocentral cavities, while deep, are less than one-fourth the length of the 
centrum, whereas in Diplodocus camegiei the pleuroccele of the thirteenth cervical is 
nearer one-half the central length. In each instance it is crossed obliquely by the 
pleurocentral lamina, which, as in cervical XII, serves also to resist the thrust of the 
prezygapophysis. 
Compared with D. camegiei, therefore, the present bone is much larger, with pro- 
portionately smaller pleurocceles. The rib arises relatively further back and seems to 
have been somewhat lighter, if one may judge from the rib facets, as the actual rib is 
not preserved. 
The neural spine is deeply bifid as in cervical XII. As the bone is now prepared, 
only the ventral and left lateral aspects are visible. A somewhat oblique view is shown 
on Plate II, Fig. 2. 
Measurements of Cervical XIII 
Barosauriis Diplodocus 
lentus camegiei Ratios 
Length over all ioosf 655* 1.53 
Height over all ' 550* 
Width across diapophyses 570 3go* . 1.46 
Centrum, length 890 655* 1.36 
anterior face, height 186* 
" " " width ca. 300$ 230* 1.30 
" posterior face, height 220* 
" " " width ca. 345$ 220* 1.57 
" circumference 840 707 1.16 
Pleuroccele, length 210 
Average ratios : Barosauriis lentus and Diplodocus camegiei 1.40 
* Peterson's measurements. 
f Length increased by crushing? 
$ Measurements from photograph. 
