312 G. Baur — Palceohatteria and the Proganosauria. 



Some important results can be reached from the study of this 

 ancient form : 



1. The ant orbital foramen or fossa is a secondary formation ; 

 all forms of Reptiles having this fossa descended from forms 

 vrithout it. 



2. The peculiar short bone in the hind foot of the Reptilia, 

 which some consider as a metatarsal 5, others as a tarsal 5, 

 certainly represents the metatarsal 5. 



3. The bones called epiplastra and endoplastron in the Testu- 

 dinata are doubtless the clavicles and interclavicle. The clavicles 

 and interclavicle of the Amniota represent the " mittleren unci 

 seitlichen Thoracalplatten " of the Stenocephalia and other 

 Batrachia. These elements must be considered as dermal ossi- 

 fications ; the connection with the shoulder-girdle is secondary. 



•i. The origin of the so-called '''■Abdominal ribs." The 

 abdominal ossicles or " ribs " are found to-day only in Sphenodon 

 and the Crocodilia ; the " abdominal ribs " of Chamceleo, Poly- 

 chus, etc., are entirely different elements. There are no 

 abdominal ossicles like those in Sjjhenodon found in Palceo- 

 hatteria, Proterosaurus, IFyperodapedon. In these we have 

 .bundles of scale-like pieces. These we have to consider as the 

 homologue of the same elements in the Stegocephalia and as 

 the abdominal ossicles in the Rhynchocephalia, Ichthyosauria, 

 Plesiosauria, Pterosauria, Crocodilia, Dinosauria, Saururse. In 

 nearly all these forms each set of abdominal ossicles consists of 

 one or two median pieces and one lateral one on each side ; 

 but in the Ichthyosauria. we find very often one median piece 

 and two lateral ones on each side. 



The idea, at first pronounced by Owen, that the plastron of 

 the Testudinata has developed from abdominal bones is very 

 probable. 



5. The foramina in the humerus of the higher Vertebrata. — 

 a. No foramen: Batrachia. 



b. Foramen entejpicondyloideum : Proganosauria, Thero- 

 mora,t Mammalia.* 



c. Foramen entepicondyloideum and foramen ectepicondy- 

 loideum : Sphenodontida?, some humeri from the Permian of 

 Pussia. 



d. Fossa e?itepicondyloidea and foramen ectepicondyloi- 

 deum : Atoposaurus, Sapheosaurus, JSTothosauridse, part. 



e. Foramen ectepicondyloideum : Testudinata, Lacertilia. 

 jSTothosauridse part, Rhynchocephalia, part. 



f Fossa ectejyicondyloidea : Belodon, Champsosaurus, Tes- 

 tudinata, part, etc. 



g. No foramen : Crocodilia, Dinosauria, Pterosauria, Ple- 

 siosauria, Pythonomorpha, Birds, etc. 



* If not lost by specialization. 



f The name Theromorpha has been changed by Professor Cope to Theromora. 



