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



the Crocodilian theory of the Ornithosaurian pelvis enunciated 

 by von Meyer and adopted by Owen and Zittel, if we first 

 conceive that the pubic bone has been practically eliminated 



Fi?. 14. 



prepubiB. 



Ventral Aspect of Pelvis of Alligator. 



from the pelvis of the Crocodile. Further evidence of this 

 elimination is, I think, to be found among existing birds and 

 among the fossil reptiles named Ornithischia, which have the 

 pubic bones less developed than among Ornithosaurs. In the 

 Igiianodon hernissartensis (fig. 15) the pubic bone is very short 

 as compared with the ischium. The pubis resembles in a general 

 way that of an embryo bird in having distinct anterior and 

 posterior limbs. The slender short posterior limb of the 

 pubis extends backward parallel to the slender ischium, as in 

 adult birds ; but the anterior limb is wider, stouter, and 

 directed forward, but is still short as compared with the 

 ischium. It is obvious that, as in Ornithosaurs, there is no 

 possibility among Ornithischia of the pubic bones meeting 

 ventrally in a median symphysis. But the wide, forwardly- 

 directed process of the pubis resembles in its extension the 

 ventral process of the pubis in many Ornithosaurs. Further 

 forward in the skeleton are found the pair of bones which 

 have been variously regarded as clavicles and sternal bones 

 in species of Iguanodon and allied genera. These bones 

 present the most remarkable resemblance in form to the pre- 

 pubic bones in Dimorphodon, and from their relation to each 

 other seen in Iguanodon I conclude that they may be identified 



