448 R. W. Iloolet/ — Igiuuiodon mantelU — Brig/isfone Bay. 



this expcansion was an adaptation for the express purpose of insuring 

 protection and support for the embryo? During the swing of the 

 tail from side to side the body must have swayed in unison, and 

 without a stiff hiteral stop the embryo would have been compressed 

 and distorted by constant thrust against the walls of the abdomen, so 

 that injury would have occurred. 



There was no symphysial union of the pubes and ischia, and the 

 pubic bone has in all the Orthopoda a decided deepening at some 

 ])ortion of its length and is directed more forward than downward. 

 The inner trochanter of the femur of Iguanodoii is so much more 

 developed than in other genera that the vertical expansion of the 

 pubis would seem to have a relation to the swaying of the viscera 

 caused by the peculiar bipedal progression of the reptile. 



In the Theropoda the median symphysial union of the pubes and 

 its prolongation along the lower anterior border formed, together with 

 the fused ischia, a cradle for the embryo, so that an expansion of the 

 pubic bone was not necessarj-. 



Moreover, the position near the proximal end of the femur and 

 weakness of the iimer trochanter seem to show that in these reptiles 

 the Avaddling was not nenrly so great as in Iguanodoii, and it is 

 a question whether the Theropoda were really habitually bipeds. 

 In the Sauropoda we find the same cradle-like pelvis, which would 

 be more suitable for the protection of the embryo and for quadrupedal 

 habits. 



If /. mantelli is the female of /. hernissartensis, then the extent of 

 the nares and the length of the tibia are features which are due to 

 sexual divergence. In regard to the strange circumstance tliat at 

 Bernissart the small form was found apart from the large forms, 

 it does not seem a more remarkable coincidence than that every 

 specimen of /. mantelU found up to the present has been smaller than 

 /. lernissartensis. 



Therefore the conclusion appears reasonable that the osteological 

 variations are sexual and that /. bernissartensis is a synonym of 

 /. mantelli. 



In conclusion, the evidence seems to prove — 



1. That /. mantelli attained the dimensions of /. hernissartensis. 



2. Tliat the differences found in the forms of the pelvic bones is 

 probablv sexual, an adaptation for the preservation of the embryo. 



3. That /. hernissartensis is a synonym of /. mantelli. 



4. That not only the body of the Iguanodon (as shown by 

 Professor L. Dollo) is a lever of the first kind, but the bones of the 

 pelvis comprise one also. 



5. That the ventral expansion of the pubes and ischia was to give 

 greater leverage power. 



6. That the direction and ventral separation of the pubes and 

 ischia were adapted for the sagging of the visceral mass when 

 adopting the erect attitude. 



7. That the prolongation and the recurving of the ischia were for 

 the support of that mass when in that position. 



8. That in the Theropoda, Orthopoda (sections Stegosauria and 

 Ceratopsia) the upright position was seldom assumed. 



