238 Prof. H. Gr. Seteley. [Dec. 8, 



bone corresponds in position with the pre-pnbic bone of Ornithosaurs, 

 which is always developed on the anterior pnbic border towards the 

 acetabulum, at some distance from the pnbic symphysis. The extinct 

 allies of the Crocodilia may throw some light upon the nature of this 

 ossification. f 



First, in the Teleosauria the bone is much more slender and less 

 expanded at its anterior end, in all the species from the Lias and 

 Lower Oolitic rocks. The diminution in size of the bone in Oxford 

 clay representatives of the group is more marked, and in some unde- 

 scribed types in the collection of A. Leeds, Esq., is reduced to a mere 

 bony style without any expansion at either end, comparable in form 

 ami substance to a lucifer match. One stage more of diminished deve- 

 lopment would obliterate the bone altogether, but no such condition 

 has yet been discovered. It has the same osseous attachment as in 

 Crocodilia, and the ischio-pubic bone is of the same type in Teleo- 

 sauria as in Crocodiles. 



In the Ornithosauria the plan of the pelvis is different. First, 

 there is the complete ossification of the three constituent bones, with 

 the ilium prolonged in front of the acetabulum as well as behind it r 

 the ischium and pubis united by symphysis, and all three bones contri- 

 buting to form the imperforate acetabulum. Secondly, there is a pre- 

 pubic ossification in front of the pubis, with a narrow attachment below 

 the acetabulum. These pre-pubic bones vary in form in the different 

 genera. In Dimorphodon they are triangular; in Cycnorhamphus 

 they are shaped like a capital and so expanded anteriorly that 



Pre-pubic bones of Cycnorha mphus suevicus, 

 after Q.uenstadt. Eestored. 



a a 

 a, attachment to the pubic bones. 



the cross bars from the two sides met in the median line; in Rham- 

 phorhynchus the shape is "Qj, an inverted capital |_, but the 

 bones of the two sides are united together into a transverse bow- 

 shaped bar. Other modifications are found in the group, but the 

 most common are approximations to the form of the pre-pubic bones 

 of crocodiles. Since these bones have the same relations to the 

 pubes which the pre-pubic bones of crocodiles exhibit, I regard them 

 as being homologous, and if the distal part of the Ornithosaurian 



