22 THE SAUROPOD DINOSAUR BAROSAURUS MARSH. 
SACRUM 
This element is represented by a portion of the fourth (?) centrum and the 
coalesced summits of the neural spines. The central fragment is extremely massive, 
with no adaptation for lightening the weight appreciable in the portion preserved. 
Measurements of the centrum are impracticable. 
The coalesced neural spines are sheared off on the apparent left side so that their 
buttresses are lacking. On the other side, however, there are three such buttresses 
which are in part free from the mass of the bone, like the flying buttresses of Gothic 
architecture. The entire summit is quite rugose, the rugosity extending down on the 
buttresses for a distance of about ioo mm. 
The antero-posterior diameter of the mass as preserved is 240 mm. ; the preserved 
height 390 mm., with no trace of zygapophyses at the level of fracture. 
There is an additional rugose nodular piece of bone which fits fairly well into the 
somewhat cleft anterior end of the coalesced spinal summits and seems to represent 
such a nodule as that figured by Osborn 4 in the sacrum of Diplodocus longus at the 
American Museum, as well as in the restoration of D. carnegiei. 
The equivalent measurements of the coalesced neural spines of Barosaurus and 
the two Diplodocus specimens are : 
Barosaurus Diplodocus 
/cuius longus D. carnegiei 
mm. mm. mm. 
Antero-posterior diameter 240 113.6 156 
Height from zygapophysis 390+ 340 450 
The much greater first dimension in Barosaurus seems to point to need for a firmer 
anchorage for the extension members of the entire vertebral fabric, correlated probably 
with the greater weight of the cervical region. (See PL VII.) 
CAUDAL VERTEBRA 
Caudal II ( Vertebra A ) . — This bone has a fine centrum showing little apparent 
distortion. But little of the neural arch is present and the wing-like diapophyses are 
gone. This vertebra is proccelous, but the curvatures are not great. Height of the 
neural canal, 36 mm. ; its width, 44 mm. The lateral aspect shows deep pleurocceles, 
that of the right side having a length of 72 mm. to a depth of 173 mm. The neural 
arch has not the proportionate antero-posterior diameter seen in the dorsals. The least 
diameter across the pedicels is 69 mm. 
Posterior aspect. — The right postzygapophysis is preserved, and corresponds in size 
and curvature to the equivalent prezygapophysis of the vertebra next to be described. 
The zygapophysis is supported by the usual postzygapophysial lamina rising above the 
neural canal. The latter, however, is distorted by crushing. Its height is 46 mm. 
' H. F. Osborn, A Skeleton of Diplodocus. Mem. Amer. Mus. Nat. Hist, Vol. I, Pt. V, 1899, Fig. 7. 
