96 THE EXTINCT BATRACHIA, REPTILIA 



Owen in Iguanodon with clavicles, and by Leidy in Hadrosaurus with the pubes. The 

 Director in the British Museum has well pointed out the possibility of such a form of 

 clavicle being probable, after a comprehension of the variations presented by the modern 

 Sauria, and the not dissimilar form in Trachysaurus and Cyclodus. Leidy, however, is of 

 opinion that similar bones in Hadrosaurus resemble rather the pubic bones of Iguana, and 

 calls them pubes, with doubt. The writer sees a much greater resemblance between them 

 and the elements called ischia by Wagner in the Compsognathus, and which are homolo- 

 gous with the posteriorly directed bone so called in birds. 



It is noticeable that in the great Dinosauria the supposed clavicles do not diminish in 

 length in the same proportion as do the humeri, as one would be led to expect were they 

 clavicles. The relative lengths in three species are as follows : — 



Inches. 



Iguanodon anglicus ; humerus, 85. 



os ischium, 29. 



Hadrosaurus foulkii ; humerus, 22.5 



os ischium, 27. 



Laelaps aquilunguis; humerus, 12. 



os ischium, 20. 



Their density and strength in the last named species are not readily reconcilable with 

 the needs of such small fore limbs. Further, in Stenopelix Myr. and Compsognathus, 

 where similar elements exist in the position of pubes and ischia, no clavicles have been 

 preserved to us. 



The more or less normal position in which these bones were found in the Maidstone 

 specimen of the Iguanodon, as given in the figure accompanying Prof. Owen's monograph, 

 has been already alluded to ; the ilia were lying parallel with each other, their extremities 

 similarly directed. The ischiadic bones lay across the ilia in their axes, the anterior dilated 

 extremities lying not far from the position of the lost pubes, the posterior directed far be- 

 hind the iliac crests, parallel to their axes. The similarity of position in both, and the 

 preservation of relation between many of the other bones, renders it probable that their 

 identification with ischia also indicates their natural relation. 



The direction of the ischia is a difficult point to determine, but may be best understood 

 by reference to those of Megadactylus and Clepsysaurus. In Hadrosaurus (see Leicly's 

 plate in Cret. Rept. U. S.) this bone consists of a long slender subcylindric shaft with 

 dilated extremity. The dilated portion thin, a part in line with the shaft and truncate, and 



