606 PROF. H. G. SEELEY ON THE DINOSAURIA OF 
the side of the centrum concave from front to back. The transverse 
width of the centrum at the notches for the sacral nerves is 14 inch ; 
the transverse width over the front of the facets for the sacral ribs 
is about 21 inches; the width of the neural canal between the pe- 
dicles for the neural arch, as preserved, is 14 inch. 
The third sacral vertebra (fig. 3,3) is smaller, with the centrum 
similarly depressed, the neural canal almostas large, the anterior 
intervertebral articular surface convex from side to side, and the 
posterior articulation similarly concave, the latter being relatively 
deeper ; the length of the centrum in the median line is 13 inch. 
The base is flattened, slightly convex in the middle portion, and 
measures 117 inch transversely. This great width, like the flat- 
tening, results from the fact that the whole of the side is occupied 
by surfaces for the attachment of sacralribs. The two pairs of these 
surfaces are divided by the grooves for the sacral nerve, which are 
only half as wide as those in the second vertebra ; these grooves are ;5; 
inch from the anterior articulation, and are directed outward, a little 
backward, and vertically downward between the facets for the sacral 
ribs as a canal 3, inch wide. The anterior of these rib-facets is the 
larger ; it is an inch deep, and not quite so long, being subquadrate ; 
the surfaces look outward, forward, and very slightly upward, and 
extend to the anterior articular surface of the centrum. The posterior 
facet is fully as deep, but not more than halfan inch in length; it ex- 
tends back to the posterior articulation, and looks outward and back- 
ward. The greatest transverse measurement is 2 inches at the middle 
of the centrum. The neural arch appears to haye been attached to 
both the anterior and posterior ends of the centrum by pedicles, which 
are coextensive with the length of the facets for the sacral ribs. 
The superior and inferior margins of the articular faces of both ends 
of the centrum are subparallel, about 58, inch deep ; but the anterior 
articulation has the greater transverse measurement, and increases 
in depth a little towards its lateral limits. The width of the neural 
canal, as preserved, is 1,1, inch, but becomes less posteriorly. 
The fourth sacral vertebra (fig. 3, 4) has greatly decreased in size. 
There is a vertical elevated ridge in the middle of the anterior articular 
surface of the centrum, on each side of which the flattened surfaces are 
slightly concave ; the outline of the articulation is reniform, it is more 
than 58, inch deep, and was about 1,3, inch wide. The under surface 
of the centrum has a conspicuous rounded median ridge, most marked 
posteriorly, and on each side the halves of the base are flattened and 
converge inferiorly. The posterior articular surface of the centrum 
is relatively narrow (because there is only one pair of facets for 
sacral ribs, and they are immediately behind the anterior articu- 
lation) ; it is 7%; inch deep in the middle, and 1,4 inch wide at the 
upper third ; the surface is concave from side to side, and most im- 
pressed in the upper part of the middle line. The neural canal 
widens in its hinder third, where it gives off a pair of sacral nerves, 
which are directed slightly backward as they pass out. The an- 
terior lateral facets for the sacral ribs are large, extend back behind 
the middle line of the centrum, and were directed forward and out- 
