354 BAUR. [Vol. IV. 



The ectopubes and entoischia remained separate, the posterior 

 branch of the entopubes became reduced ; ectopubes and ecto- 

 ischia co-ossified with plastron : Pleurodira. 



The pelvis of Sphenodon not only explains the pelvis of the 

 Testudinata, but also that of the Squamata and Ichthyosauria,^ 

 in which entopubes and entoischia become far separated. 



The pelvis of the Aetosauria, Belodontia, Megalosauria,^ Ceti- 

 osauria,^ is also easily referable to that of Sphenodon. 



Iguanodontia^ and Birds have become modified ; in these 

 forms the entopubes have taken a parallel direction to the 

 entoischia. The ectopubis (pectinal process, praepubis) is more 

 or less developed, being directed forwards and outwards, in 

 the Agathaumidae (Ceratopsidae) the entopubes have become 

 exceedingly reduced, the ectopubes greatly developed. In 

 Birds the ectopubes are in a very rudimentary condition, and 

 may be placed functionally on the ilia. 



But Sphenodon does not offer the most original form of a 

 pelvis in the higher vertebrates. The Proganosauria show con- 

 ditions still more primitive. In Palaeohatteria, for instance, we 

 seem to have the gastroid cartilage very much more developed. 

 The entire space between pubes and ischia seems to have been 

 occupied by the gastroid cartilage. In Mesosaurus, an aquatic 

 Proganosaurian, we have conditions resembling the Plesiosauria. 

 In these forms the gastroid cartilage was probably interrupted, 

 a distinct mesogastroid being present. 



The pelvis of the Theromora can be explained by the condi- 

 tion seen in Palaeohatteria. The ossification of pubes and ischia 

 extended more and more, until the whole median portion of the 

 gastroid cartilage was absorbed, only leaving a small obturator 

 foramen. In this group pubes and ischia form a single broad 

 plate, separated by a suture in which also the obturator foramen 

 is placed. Still here we have the pubis turned forwards. 



In Mammals the entopubes are turned backwards and united 



1 I may mention here that I have no doubt that the Ichthyosauria possessed, like 

 the Rhynchocephalia, a small cartilaginous sternum. The whole morphology of the 

 shoulder girdle strongly supports this opinion. 



2 I consider, with Seeley, the Dinosauria as an absolutely unnatural group, which is 

 to be split into three distinct orders, — the Megalosauria, Cetiosauria, Iguanodontia, 

 corresponding to the Dinosaurian orders Teropoda, Sauropoda, Orthopoda. The 

 Dinosauria are comparable to the Enaliosauria, which contained also two entirely 

 different groups, the Ichthyosauria and Plesiosauria. 



