﻿KIMMERIDGE CLAY. 



79 



" Now, in all the Dinosauria which I have yet examined, the ilium extends far in 

 front of the acetabulum." 1 



To the first of these averments it needs only an elementary acquaintance with compa- 

 rative osteology to reply, that in all Crocodilian Reptiles the ilium is prolonged in front 

 of the acetabulum, and to an extent nearly equal to that in which it is produced behind 

 the acetabulum. Reference to the well-known figure in the ' Ossemens Possiles,' which I here 

 reproduce (woodcut, fig. 13, u) exemplifies this fact : Cuvier has been careful to mark with 

 the letter ' a ' the antacetabular part of the ilium which the advocate of the avian affinities 

 and bipedal progression of the Dinosauria denies to it and to all other Reptiles, Dinosauria 

 excepted. 



The true characteristic of the ilium in Dinosauria is the distinction of the super- 

 acetabular (PL XIX, r) from the antacetabular (ib., 62') parts of the bone, with the anterior 

 extension and subsidence, in some species, of the former upon the dorsal surface of the 

 latter. 



As to the proportions of the ant- and post-acetabular extensions of the ilium, they 

 vary in known Dinosauria .- the post-acetabular production {PL XIX, 62") is shorter in 

 Omosaurus than in Scelidosaurus, and is shorter in Scelidosaurus than in Jguanodon. 



From the importance assigned by Professor Huxley to iliac characters, in the con- 

 clusion he advocates, a non-anatomical reader might infer not only that no other Reptiles, 

 but that no other warm-blooded Vertebrates save Birds, had the ilium extended, as in 

 Dinosaurs, far in front of the acetabulum. 



And yet an impartial quest of the affinities of these huge terrestrial Beptilia would 

 impel the seeker, having such end solely in view, so to extend his comparisons. In 

 Mammals " the ilium is prolonged in front of the acetabulum," which, as in Reptiles, " is 

 either wholly closed by bone or presents a fontanelle." 



In the spiny Monostremes (woodcut, fig. 15, Echidna) the ilium {g) extends far in front of 

 the acetabulum [h), and furnishes only an arched roof of that cavity, the inner wall of 

 which (0 remains membranous, as in the Bird. The pubis (a), after extending haemad 

 (forward or downward) to the pectineal process (c), bends there to be continued back- 

 ward, as in Ornithorhptchus. As a rule all Mammals resemble Birds in a backward 

 extension of more or less of both pubis and ischium, from their iliac articulations. 



Thus the character asserted to be peculiar to Dinosauria among Reptiles exists in the 

 Crocodilian order of that cold-blooded class ; and, amongst warm-blooded Vertebrates, it 

 is common to Mammals with Birds. 



In my ' Anatomy of Vertebrates ' I remarked, " the transference of the weight of a 

 horizontal trunk upon a single pair of legs necessitates an extensive grasp of the trunk- 

 segments. When the legs require to be pulled far and strongly back, as in diving and 

 cursorial motions, the origins of the requisite muscles are extended far behind the limb's 



1 'Quarterly Journ. Geol. Soc.,' vol. xxvi, 1870, p. 26. 



