1 6 THE SAUROPOD DINOSAUR BAROSAURUS MARSH. 
postspinal lamina, for about ioo mm. There is an equivalent prespinal lamina, much less 
pronounced, and about 60 mm. long: In the later dorsals these laminse become highly 
rugose and of equal dimensions front and rear. They must have formed the insertions 
of powerful connecting tendons, the principal extension members of the fabric (see PI. 
Ill, Figs. 1 and 2, PR.L. and POX.). The first dorsal of Barosaurus is thus 
transitional in character between the typically cervical and dorsal vertebrse. 
As compared with the first dorsal of Diplodocus, that of Barosaurus is char- 
acterized by a relatively shorter centrum, with proportionately somewhat larger 
pleurocceles and more pronounced horizontal laminae on the centrum. The bone in 
Barosaurus appears less massive, that is, more deeply sculptured and lightened. The 
position of the rather small capitular rib facet near the lower margin of the centrum 
is essentially the same. That of the tubercular facet must also have been similar, but 
in this instance the actual facet is not preserved. 
Measurements of Dorsal I 
Barosaurus Diplodocus 
lentus carnegiei Ratios 
mm. mm. 
Length over all 620 600* 1.03 
Height over all Sgof 68o*-638 0.87 
Width across diapophyses 610* 
Centrum, length 470 525* 0.89 
anterior face, height 165 250* 0.66 
" width 3 28t 265* 1.24 
" circumference .- 772§ 8oo§ 0.9s 
posterior face, height 250 250* 1.00 
" width , 350 245* 1.42 
" circumference 980 780* 1.25 
Pleurocoele, length 195 
height 59 
Width across prezygapophyses 530 440 1.20 
Width across postzygapophyses 460 374 1.23 
Neural spine, depth of cleft 246 
Average ratios : Barosaurus lentus and Diplodocus carnegiei 1.06 
* Peterson's measurements ; others taken from Hatcher's Plate VII. 
t Reduced by crushing. 
t Taken from photograph, not original. 
§ Calculated. 
Dorsal IV (Vertebra H) (PI. Ill, Figs. 4-6). — This bone is well preserved except 
for the neural spines and the distal ends of the diapophyses, and shows but little 
crushing. In certain respects it resembles dorsal III of Diplodocus, in others dorsal IV. 
It resembles dorsal III in the position of the capitular rib facet, which is borne on the 
upper margin of the centrum. This bone also resembles dorsal III in general propor- 
tions, but differs mainly in that the postzygapophyses are complicated by the presence 
of an hyposphene-hypantrum articulation as well. This supplementary articulation first 
appears in dorsal IV of D. carnegiei. The centrum of the bone under consideration 
is short, with deep but small pleurocceles, their small size being due to their being 
partly obliterated by the capitular rib facets somewhat as in dorsal III of Diplodocus. 
In dorsal IV of Diplodocus, however, the large facet almost completely obliterates the 
