In the Ophidians and some Saurians the pelvis, like the corresponding extremities, is totally wanting.
In the Chelonia,—the fresh-water, and the mud Tortoise, or Trionyr, have a sacrum composed of three pieces, soldered, like the dorsal ver tebrx, to the back-plate. Their long transverse processes project from it, and unite in a tuber cle at their apices, to which the ilia are attached. The caudal vertebrm are numerous.
The ilia ( fig. 108. a.) are short, thick, curved roundish and clubbed inferiorly, and are di rected outwards, forwards, and downwards, extending under the back plate directly be tween the sacrum (at i) and the acetabula. In the Tortoise and Trionyx they are moveable upon the sacrum forwards and backwards. From the acetabula, the ischia (c), larger than the ilia, pass, almost at a right angle, backwards and inwards, and unite in a median symphysis (d), forming the real pelvic circle, and present ing a sharp angle posteriorly in the Trionyx ( f) and fresh-water Turtle. In the land and fresh-water Tortoise this symphysis is continu ous anteriorly with the inter-pubic (e), forming with it a cross-shaped suture, and the ob turator foramen on each side is distinct and separate ; but, in the Turtle and Trionyx, as in most reptiles, the inter-pubic and inter-ischi atic symphyses are separated and connected by cartilage only, and thus, in the dry bones, the obturator foramina are coalesced in one large opening, and the pubes and ischia have the appearance of large ribs connected at their ventral extremities. The pubes (b) are the largest of the bones in the reptile pelvis, and, as seen in the Turtle, pass each from the acetabula as a thick bone, which expands as it passes downwards into a broad plate, and divide,s into an inner portion which unites with its opposite fellow in a syrnphysis (e,e') and an outer portion, free and directed ex ternally 0). In the Chelydes all the pelvic bones are ankylosed to the plastrum or to the back-plate ; but in the others, the ischia and pubes are connected to the plastrum by liga ments only. The anterior pelvic opening in the Chelonia is directed upwards and forwards.
The pelvis of the fossil Plesiosaurus is very like that of the Tortoise, with narrow, small, and weak ilia, with the fan"-like, spreading ischia, and large square pubes uniting in a common symphysis, by a crucial suture. The pelvic and shoulder bones have a great resemblance in the Chelonian as well as in the Saurian reptiles.
Of the Saurian reptiles the Crocodiles have two sacral vertebrm with large spines (fig. 109. a, a'), which support the ilia by strong prismatic apophyses, ankylosed together at the ends, and separated by a suture, in the young animals, from the bodies of their vertebne. The caudal
bones in all the Saurians, are very numerous.
The ilia (b) are very short, and in some species almost cuboid, slightly bent, with an inward concavity, and directed downwards and a little forwards, but almost at right angles to the spine, with the superior angle (e) projecting backwards. The ischia (c) are long, and directed, like the sides of an isosceles triangle, downwards and inwards, uniting in a median symph) sis (I), and much resemble the coracoid bones of the shoulder. The acetabula of the crocodile look di rectly outwards, have strong inter-articular ligaments, and are formed only by the ilia and ischia, the latter presenting, just below the acetabulutn, anterior apophyses which support the pubes. The pubes (d) are directed much forwards, downwards, and towards each other, but do not touch in the median line, being united only by the abdominal aponeu tached. The pubes and ischia are short and oblong, and so approximated as to leave no obturator opening.
Upon the pubic spine, in the Cameleon, are two cartiliwes, which have been stated by Duges to be of a marsupial character.
rosis (h). They are connected by the anterior border with the posterior abdominal ribs (g).
The Lizards have, like the crocodiles, two sacral bones, as in the Iguana and Great Monitor. In many Lizards the sacral trans verse processes (fig. 110. A, a) are very long, and, being articulated by suture to the bodies of the vertebrm, appear, at first sight, like additional ilia. This is particularly the case in a fossil specimen recently dis covered by Sir Charles Lyell.* The ilia (b) are directed forwards and downwards, and the su perior extremity projects backwards in a trun cated point (e). The ischia (c) are larger, and directed backwards at a great angle with the ilia. uniting in a truncated median symphysis, which is separated from that of the pubes ; so that the obturator foramina are divided only by ligament (g), and communicate in the dry bones. In some Lizards the ischia present posteriorly a spinous projection. The pubes participate with the ilia and ischia, in the for mation of' the acetabula, present a spine at their cotyloid extremity (d), curving down wards and outwards, and unite in a very narrow symph) sis ; but in the Monitors and Sauve-gardes the pubic symph)sis is distin guished by its greater breadth and truncated form (f). The ilio-pubic angle is about 160°, retirinc, posteriorly in the Great Monitor Lizardb, and the ilio-ischial angle is very acute, being 60° only (see fig. 112. 13.).