﻿KIMMERIDGE CLAY. 



03 



The length of the antacetabular part of the ilium in Scelidosaurus 1 more resembles 

 that in Omosaurus, but it is narrower and extended more in the axis of the trunk, or is 

 less inclined outward. The corresponding part of the ilium in Cetiosanrus resembles in 

 breadth that of Omosaurus. In this the acetabular cavity (62) is thirteen inches in longi- 

 tudinal, nine inches in transverse extent. Its outer and hinder border subsides at e, 

 and the cavity is continued upon the superacetabular surface of r t the break in the 

 boundary being somewhat analogous to the cleft in the more developed border of the 

 Mammalian acetabulum for the passage of vessels to the intra-acetabular synovial mass. 

 The lower or haemal part of the cavity is completed by the ischium (ib., 63) } which 

 articulates syndesmotically with the surface (J>, e). There is no surface for the articulation 

 of a pubis with the ilium, the Omosaurus in this respect corresponding with the 

 C'rocodilia. In the breadth also of the ilium as compared with the length that bone of 

 Omosaurus comes nearer to the Crocodilian than to the Lacertian type. 



And, again, in the extent to which the ilium is prolonged in front of the acetabulum 

 the Crocodiles 2 depart less from the Dinosaurs than do the Lizards. In Lacerta 

 nilotica, e.g., the ilium is prolonged in front of the acetabulum to an extent equalling 

 only that of the acetabular excavation of the same bone. 



§ 12. Ischium. — This bone (PI. XIX, 63, and PI. XX figs. 1 — 3) offers the structural 

 type of that in Chelonia and certain Lacertilia {Uromastyx, e.g., PI. XX, figs. S and 9, 63), 

 in its ' tuberosity ' or posterior process (c) ; but, in its slenderness or relation of breadth to 

 length, it exceeds that in any Lacertian or other (to me) known forms of existing Reptile. 



Of the iliac articular end of the right ischium but little is exhibited, the bone (G3, 

 PL XIX) having been pressed forward and behind the part of the acetabulum from 

 which it has been dislocated. The process ( c ) answering to that so marked in 

 Uromastyx, in the more perfect left ischium (PI. XX, fig. 8), comes off nearer the 

 articular end than in the Lizard. The rest of the bone is simply styliform and straight, 

 having no process crossing, as in Birds, the obturator interspace between ischium and 

 pubis. The smooth concavity on the under or haemal surface of the expanded end, 

 articulating with the ilium, contributes about a fourth part of the cavity for the head of 

 the femur. The end of the process ( c ) is rough, thickened, of an elongate subtriedral 

 form, 2^ inches by 1 inch ; the opposite or fore-end of the expansion has a 

 rough syndesmotic surface for the attachment of a similarly roughened end of the 

 pubis. The breadth of the ischium, including these processes, is 13 inches; from 

 this part the bone quickly contracts to a narrow plate. The hind margin of this plate 

 (ib., fig. 1, e) is moderately thick and rounded, whence the bone thins oft 7 to an edge in 

 front (ib.,/). The haemal surface is flat or feebly concave, transversely, and is smooth 

 (PI. XX, fig. 1). The upper or neural surface is, transversly, rather convex, save where it 



1 Monog. cit., p. 15, pi. vi, fig. 1. 



2 Cuvier, ' Ossemens Fossiles,' 4to, 1824, vol. v, pi. iv, fig. 15, a. 



