HATCHER: OSTEOLOGY OF HAPLOCANTHOSAURUS by) 
oblique nor intersecting laminee. There is no infracentral cavity. The capitular 
rib facet is nearly circular and slightly pedunculate. Its position is beneath the 
anterior border of the pleurocentral cavity. 
The neural arch is decidedly higher than in the posterior cervicals. The dia- 
pophyses are more widely expanded and support at their extremities small triangular 
tubercular rib facets which face outward and a little downward. These rib facets 
are not pendant as they are in this and the two succeeding dorsals in Diplodocus. 
The anterior and posterior zygapophyses are both somewhat more elevated than the 
diapophyses and they are supported laterally by the anterior and posterior blades 
of the horizontal laminee which are subequal and unite at an obtuse angle to form 
and give support to the transverse process or diapophysis. Throughout about two 
thirds of its length the external margin of the anterior blade of the horizontal lamina 
presents a greatly expanded rugose surface, which no doubt served for the muscular 
attachment of the scapula. From below, the transverse process is supported by the 
short, rather slender inferior blade or branch of the diapophysial lamina which runs 
obliquely downward and forward to unite with the superior branch of the prezyga- 
pophysial lamina, while an extended and powerful oblique lamina runs obliquely 
downward and backward, uniting with the lateral wall of the neural arch and giv- 
ing additional support to the transverse process. The pre-, infra- and postdiapo- 
physial cavities are all deep and well enclosed, while the supradiapophysial cavity 
is shallow and left open anteriorly. 
Seen from in front this vertebra appears low with the transverse processes, zyga- 
pophyses and neural spine greatly expanded. The neural spine is low and extremely 
broad. The apex on one side is injured. It is quite simple, not at all bifurcated 
and with a broad, rugose, median surface. ‘The anterior aspect of the spine is strongly 
convex transversely throughout its entire length. The articular surfaces of the an- 
terior zygapophyses are elliptical in outline, with the transverse diameter the greater. 
Between the anterior zygapophyses there extends a thin lamina having the appear- 
ance of a broad shelf or platform. Inferiorly the zygapophyses are supported by 
the powerful inferior branches of the prezygapophysial laminze while the superior 
branches of these laminze are rudimentary. The infrazygapophysial cavity is deep 
and simple, the supra- is quite shallow. 
Posteriorly there is a deep cup on the centrum for the reception of the ball of 
the succeeding vertebra. The articular surface of the posterior zygapophysis faces 
downward and outward. 
The postzygapophysial lamine are branched, the internal and smaller of these 
branches from the zygapophyses of the opposite sides meet in the middle line and 
