Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/102

 96 THE EXTINCT BATRACHIA, REPTJLIA 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 clairicles. The relative lengths in three species are as follows Iguanodon anglicus ; Hadrosaurus foulkii ; Laelaps aquilunguis; humerus, os ischium, humerus, os ischium, humerus, os ischium, Inches. 85. 29. 22.5 27. 12. 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 Compsog,nathus, 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 3Iegadactylus and Clepsysaurus. In Hadrosaurus (see Leidy'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