LIASSIG FORMATIONS. 
7 
ward, looks downward, outward, and a little backward, the process being slightly 
inclined that way. The margin of the articular end of the centrum is better defined 
than in the neck ; about a line’s breadth is, as it were, shaved off ; the rest of the sur- 
face (fig. 2, c) is very slightly concave, sometimes undulated, always nearly flat, and 
with a small central depression, or a tendency there to a tubercle. The length 
of the dorsal region in the skeleton (Tab. I) 8 feet 9 inches long, is 2 feet 6 inches ; 
the number of dorsal vertebrae is twenty-one. 
Sacrum. — Two vertebrae (ib., s) succeeding the dorsals are distinguishable, through 
the greater thickness and straightness of their short pleurapophyses, as sacral; these 
elements abut against, or afford ligamentous union to, the iliac bones. 
Caudal series. — The caudal vertebrae (Tab. I, c d. Tab. IV, figs. 3 — 9) are shorter in 
proportion to their breadth than the others ; the centrum approaches to a cubical figure, 
the under surface (figs. 4 and 7) becoming broad and flattened ; and the contour of the 
terminal articular surfaces shows a similar tendency to flattening, giving a transversely 
extended quadrate figure, with the angles rounded off (figs. 5 and 8) ; the margin is 
thicker, more rounded off, less defined than in the dorsal vertebrae. The articular surface 
itself is more concave than in the antecedent regions of the backbone, and becomes 
deeper in the terminal subcompressed vertebrae (fig. 9) ; the movements of the tail 
in swimming having been helped here by a greater amount of yielding intervertebral 
substance, approaching in the same degree to the condition of the spine in fishes. 
The costal surface (figs. 3, 6, pi) is elliptic, with the long axis subvertical, the margin 
prominent, the cavity simple and rough for the ligamentous attachment of the riblet ; it 
is situated on the upper half of the centrum close to the neurapophysis, the outer end 
of the base of which contributes to the upper part of the margin in the anterior 
caudals (fig. 5, d). 
The pleurapophyses in this region (Tab. IV, 5, pi) do not expand terminally, 
as in the neck ; they are short, thick, and straight, simulating transverse processes ; 
their non-confluence with the centrum exemplifies the minor vigour of vital co-ossifying 
influences in terminal parts. 
The haemapophysial surfaces (fig. 3 h') impress the inferior angles of the 
posterior surface of the centrum ; occasionally, where a haemapophysis has become 
anchylosed and broken off, its adherent base gives the appearance of a process from 
that part of the centrum (ib., figs. 6, 7, 8, h). The venous foramina are at the lower 
part of the sides of the centrum. The neural arch (figs. 3, 5, n) rapidly diminishes in 
size and in the length of the neural spine, ns. The zygapophysial surfaces become more 
vertical, the anterior, 2 ;, looking inward ; the posterior zygapophyses, d, are the first to 
disappear. The hsemapophyses (fig. 5, h) are free, and were ligamentously connected 
with the centrum above and with each other below, circumscribing there the hremal 
canal. The proximal surface is expanded, with a subtriangular facet cut obliquely at 
the anterior part for articulation with its own surface, and with a smaller, less definite 
