HATCHER: OSTEOLOGY OF HAPLOCANTHOSAURUS ile 
neural spine. The entire length of the spine is represented, but the margins, except 
the posterior, are weathered away and have been restored in plaster. It thus 
happens that the drawing represents the top of the spine less complete than it 
actually is. 
The centrum was opisthoccelous with the cup moderately deep and the ball at the 
anterior extremity rather more convex than represented in the drawings _ It is con- 
stricted medially, both laterally and inferiorly, and the inferior surface presents a 
broad median longitudinal ridge. There are no infracentral cavities. The pleuro- 
central cavities are large, irregularly triangular in outline and very deep, with the 
dividing median septum reduced to a thin lamina. 
The neural arch is high, much constricted transversely and much shorter antero- 
posteriorly than the centrum. On the anterior lateral margin of either side it sup- 
ports an elongated, sessile, capitular rib facet situated midway between the anterior 
zygapophyses and the superior border of the centrum. ‘This facet is quite unlike 
that of the succeeding dorsals, it is very distinctive and is most like that of the sixth 
dorsal in H. utterbackii to be described later, as compare Plates I. and II. 
The transverse processes are high and directed obliquely upward and outward at 
an angle of about forty-five degrees. At their extremities they bear tubercular rib 
facets which face outward and a little upward. Inferiorly the transverse process is 
supported by a powerful lamina arising from the posteroexternal border of the 
neural arch and forming the greater portion of the broad posterior surface of the 
transverse process. Although this lamina occupies a position identical with that of 
the inferior blade of the diapophysial lamina in the corresponding dorsal of Diplo- 
docus, nevertheless it is clearly homologous with the oblique lamina of the first dorsal 
of this skeleton. In this vertebra the diapophysial lamina, only the inferior branch 
of which is represented in the last cervical and first dorsal described above, has be- 
come quite obsolete. There is, in Haplocanthosawrus, no division of the anterior 
blade of the horizontal lamina into superior and inferior branches such as has been 
shown to be the case in the anterior dorsals of Diplodocus carnegu. ‘This fact at 
once distinguishes that lamina marked a/ and d/, in the first dorsal and last cervi- 
cal as the diapophysial and that marked o/, as an oblique lamina, though in no 
sense to be considered as homologous with the oblique lamina that in the middor- 
sals of Diplodocus carnegui gives support posteriorly and inferiorly to the capitular 
rib facet. 
The anterior blade of the horizontal lamina is long and broad, the posterior 
short and narrow. There is a short and narrow superior blade of the diapophysial 
lamina invading the bottom of the deep supradiapophysial cavity shown at d/, in 
