238 Prof. H. G. Seeley on the Ornithosaurian Pelvis. 



This divergence of type, which is not entirely to be connected 

 with functional modification of structure, is conspicuous 

 between ten'estrial and aquatic Amphibia, between Crocodiles 

 and Chelonians, and Chelonians and Lizards, in a way not 

 known between orders of mammals or birds. 



The extinct orders of animals commonly known as the 

 Fossil Eeptilia, which till the morphological interval between 

 Amphibians and Mammals, Reptiles and Birds, are all marked 

 by distinctive forms or plans of the pelvic bones, though their 

 characters have not yet been fully described or established in 

 all these groups. Enough, however, is known to show that 

 while the pelvic characters appear to approximate the Ornith- 

 iscliia to embryonic birds, the Saurischia approximate to 

 types like Sauropterygia, Anomodontia, and Ornithosauria. 

 It is, however, impossible to consider the significance of these 

 resemblances so long as the true nature of the pelvis in the 

 Ornithosauria remains undetermined ; and as my own views 

 have undergone some change since the ' Ornithosauria ' was 

 published in 1870, I propose to set out the evidence obtained 

 m 1878, when, with the aid of the Government-Grant Fund 

 of the Royal Society, I studied the Ornithosaurs from the 

 Lithographic Stone and the Lias preserved in the museums of 

 Germany, and the conclusions which this study suggests. 



The chief difficulties consist in determining whether the 

 Ornithosaurian pelvis is composed of three bones or four 

 bones, whether the pubic bone enters into the acetabulum for 

 the femur, and how the fourth bone, if such exists, is condi- 

 tioned Nvith regard to the other elements of the pelvis. Von 

 Meyer is the earliest writer on this subject whose opinion need 

 be quoted. I have stated his views fully in my " Remarks 

 on Dimorpliodon " ^, and they might be left with the refuta- 

 tion then formally given, if it were not that Professor Karl 

 Zittel, in his ' Handbuch der Palfeontologie,' has (pp. 786, 

 787) repeated the original errors both by description and 

 figures. Professor Zittel quotes the ' Ornithosauria ' and my 

 " Remarks on Diinorphoclorij^ yet adopts the view that in 

 Ornithosaurs the ilium and ischium combine to inclose the 

 ovate acetabulum, entirely excluding the pubis, which is then 

 regarded as a free bone meeting its fellow in the median line. 

 This free bone I have regarded as the prepubic bone. In a 

 matter of this sort the weight of authority in favour of a 

 point of structure, which is not a matter of interpretation, but 

 of fact, goes for nothing. Tliere is no doubt that Zittel has 

 the support of Sir R. Owen ; but I do not so read the views 



* Ann. & Mag. Nat. Hist., Angu=^t 1870. 



