The first sacral shows the transversely extended and concave articular surface of the centrum (Pl. VII. fig. 1, _c_); the subcircular pit (ib. _p_) for the head of the rib is behind the middle of the side of the centrum, at its upper part; the inferior surface is ridged lengthwise; and a transverse low but sharp ridge defines the posterior boundary, the depressions in front of which indicate the hindmost origins of the subvertebral muscle (longus colli?). The anterior outlet of the neural canal (ib. _n_) is subcircular in one specimen, vertically elliptic in others, and 3 lines or less in transverse diameter. From the sides of the neurapophyses stretch out the strong buttresses of bone which blend with the under part of the ilia, giving off from the fore part of their base the præzygapophyses (ib. _z_), and from the back part of their apex the surface (ib. _d_), or part of it, for the tubercle of the last moveable rib, the ilium in the latter variety affording the rest of that surface. The fore part of the strong neural spine (ib. _ns_) is roughened by a syndesmotic surface; it rises to a height of 14 lines, curving forward, and is confluent at its summit with the approximated anterior margins of the ilia. A continuous track of bone, forming a smoothly obtuse longitudinal ridge, represents the summits of the succeeding sacral spines (ib. fig. 2, _ns_) to the hindmost vertebra of the series, without any trace of their primitive division; but this track rises, posteriorly, above the shallow channel on each side, in which are the foramina (ib. _o_), indicating most of the constituent vertebræ. The second sacral vertebra abuts against the ilium by a pleurapophysis (ib. fig. 1, _pl_ 2), as well as a diapophysis (ib. _d_ 2); but the former is a slender, straight filament, or narrow plate of bone, confluent at both ends. In the next two vertebræ the pleurapophysis (ib. _pl_ 3 & 4) assumes more breadth and robustness, but is short and straight, abutting against the inner surface of the ilium an inch in advance of the acetabulum. The first of these rib-buttresses inclines forward, and is completely confluent with the ilium; the thicker one (ib. _pl_ 4) has retained part of its primitive ligamentous attachment to the ilium: the proportions of both are subject to some variety.