﻿GREAT OOLITE. 



41 



have approached that of Hglceosaurus" 1 Perhaps a nearer one would be the sacrum in 

 Scelidosaurus? 



In either comparison the length of the sacrum is not to be estimated by that of the 

 ilium. In Scelidosaurus, e.g., in which the number of sacral vertebrae is ' four/ the parts 

 of the ilium anterior and posterior to the sacro-iliac symphysis, or surface of junction 

 with such vertebrae, give to that pelvic bone almost twice the length of the sacrum. The 

 length of this part of the spine in Scelidosaurus is 10 inches, whilst that of the ilium is 

 18 inches, " a part, apparently a small one, being wanting from both extremities " of the 

 iliac bone. But, on this basis, we may allow to the ilium of 45 inches length a 

 sacrum of 24 inches, or one of four vertebrae, each 6 inches in length. It is not 

 probable that a saurian with iliac bones between 3 and 4 feet in length, and thigh-bones 

 between 5 and 6 feet in length, would have a sacrum reduced to the crocodilian formula 

 of two vertebrae. 



Admitting, then, that more numerous sacrals, such as the Chelonians show, are not 

 the sole and may not be the chief character of Dinosauria, and that the generalisation 

 signified by that term is a passing one, denoting a step in the progress of knowledge of 

 the extinct Reptilia ; and supposing that it should be now limited to saurian genera, 

 combining, with four or more sacrals, the alternating or interlocking arrangement of the 

 autogenous vertebral elements — as in Bothriospondglus, Megalosaurus, Iguanodon, Hglteo- 

 saurus — the question to be solved is : — " Does such arrangement characterise the sacrum 

 of Cetiosaurus ?" Have we, in the absence of any certain or definite knowledge of the 

 cranial and dental characters of the genus, grounds for determining its ordinal 

 relations to the Dinosaurs, Crocodiles, Sauropterygians, Ichthyopterygians, Lacertians, 

 &c. ? I am disposed to wait for such additional evidence, admitting, meanwhile, the 

 faculty of terrestrial progression in a superior degree to that of the amphibious Crocodiles ; 

 nevertheless, the habitual element of the Cetiosaur may have been, and I believe to have 

 been, the waters of a sea or estuary. And I may here repeat the remark on the initial 

 evidence of the species : — " The main organ of swimming is shown, by the strength and 

 texture and vertical compression of the caudal vertebrae, to have been a broad vertical 

 tail ; and the webbed feet, probably, were used only partially, in regulating the course of 

 the swimmer, as in the puny Amblgrhgnclius of the Galapagos Islands, the sole known 

 example of a saurian of marine habits at the present period." 3 



In fact, to the characters of the caudal vertebrae of Cetiosaurus longus known to me at the 

 date of the above-quoted ' Report,' viz. — " post-zygapophyses represented by hollow pits," 

 " slight concavity of both articular ends of the centrum, moderate compression of the sides 

 between the expanded ends, which are subcircular, 4 the under surface concave lengthwise, 



1 Op. cit., p. 257-8. 



2 'Monograph on a Dinosaur of the Lower Lias, Scelidosaurus. , Palseontograpliical Society's volume 

 for 1860 (issued 1863), tab. vi, p. 6. 



3 ' Report,' &c„ p. 102. i lb., pp. 101, 102. 



