But in what follows these leading definitions, the terms are descriptive merely. Now in Comparative Anatomy, an important object of terms is, to express what part of the type each bone represents--to answer the question, _what_ is it? before we proceed, assuming that we know what it is, to describe its shape. The difficulty of this previous question is very great when we come to the bones of the head; and when we assume, as morphology leads us to do, that the heads of all vertebrated animals, including even fishes, are composed of homologous bones. And, as I have already {351} said in the History (b. xvii. c. 7), speaking of Animal Morphology, the best physiologists are now agreed that the heads of vertebrates may be resolved into a series of vertebræ, homologically repeated and modified in different animals. This doctrine has been gradually making its way among anatomists, through a great variety of views respecting details; and hence, with great discrepancies in the language by which it has been expressed. Mr. Owen has proposed a complete series of terms for the bones of the head of all vertebrates; and these names are supported by reasons which are full of interest and instruction to the physiologist, on account of the comprehensive and precise knowledge of comparative osteology which they involve; but they are also, as I have said, interesting and instructive to us, as exemplifying the reasons which may be given for the adoption of words in scientific language. The reasons thus given agree with several of the aphorisms which I have laid down, and may perhaps suggest a few others. Mr. Owen has done me the great honour to quote with approval some of these aphorisms. The terms which he has proposed belong, as I have already said, to the _Terminology_, not to the _Nomenclature_ of Zoology. In the latter subject, the Nomenclature (the names of species) the binary nomenclature established by Linnæus remains, in its principle, unshaken, simple and sufficient. I shall best derive from Mr. Owen's labours and reflexions some of the instruction which they supply with reference to the Language of Science, by making remarks on his terminology with reference to such aphorisms as I have propounded on the subject, and others of a like kind.