430 ON THE MODIFYING INFLUENCE OF A HIGHEK FORM OF LIFE.
mechanism, nor by thick sutural margins ; and the advantages of diminished weight and increased freedom of inflection of the trunk are still possessed unexceptionally by the procoelian Crocodiles.
Prof. Owen remarked, in reply to Sir Philip Grey-Egerton, that the objection that other quadrupeds besides hoofed ones trod the Tertiary earth no doubt would apply to the quotation introductory to his paper, but that was made merely to exemplify the meaning of the title. "A change of characters concomitant with change of density in the earth's surface" was analogous to " a change of characters concomitant with the introduction of new forms on that surface." But the dif- ference between the quotation and the subject-matter of the paper was that the changes of density were hypothetical and unproven, whereas the coming-in of large mammalian quadrupeds at the Ter- tiary period was an accepted fact.
