THE ORNITHOSCELIDA. 225 



In Iguanodon the slenderness and prolongation are even car- 

 ried beyond what are to be seen in Birds. I am disposed to 

 think, however, that, as was certainly the case in Eypsilopho- 

 don, the ischia united in a median ventral symphysis in all the 

 Ornithoscelida. 



3. In all reptiles the pubis is inclined forward, as well as 

 downward, toward the ventral median line. In all, except the 

 Crocodile, it takes a considerable share in the formation of the 

 acetabulum ; and the ossified pubis unites directly with its 

 fellow in the middle line. 



The pubes of Gompsognathus are, unfortunately, obscured 

 by the femora. They seem to have been very slender ; and to 

 have been directed forward and downward, like those of Liz- 

 ards. Some lizards, in fact, have pubes which, if the animal were 

 fossilized in the same position as Gompsognathus, would be very 

 similar in form and direction. Hypsilophodon, however, affords 

 unequivocal evidences of a further step toward the bird. The 

 pubes are not only as slender and elongated as in the most 

 typical bird, but they are directed downward and backward 

 parallel with the ischia, thus leaving only a very narrow and 

 elongated obturator foramen, which is divided by the obtura- 

 tor process. 



It remains to be seen how far the hypsilophodont modi- 

 fication extended among the Ornithoscelida. The remains of 

 Gompsognathus and of Stenopelyx tend to show that it was 

 by no means universal. 



As to the hind-limb, in existing reptiles — 



1. The proximal end of the tibia has but a very small, or 

 quite rudimentary, cnemial crest, and it presents no ridge for 

 the fibula on its outer side. 



2. The flattened sides of the distal end of the tibia look, 

 the one directly forward, or forward and inward; and the 

 other backward, or backward and outward. And when the 

 posterior edges of the two condyles of the proximal end of the 

 tibia rest on a flat surface which looks forward, the long axis 

 of the distal end is either nearly parallel with that surface, or 

 is inclined obliquely from in front and without, backward and 

 inward. 



3. There is no depression on the anterior face of the tibia 

 for the reception of an ascending process of the astragalus. 



4. The distal end of the fibula is as large as, or larger than, 

 the proximal end, and articulates largely with a facet on the 

 outer part of the astragalus. 



5. The astragalus is not depressed and flattened from above 



