But further: there is another kind of homology which Mr. Owen calls _General_ Homology, according to which the primary type of a vertebrate animal is merely a series of vertebræ; and all limbs and other appendages are only developements of the parts of one or another of the vertebræ. And in order to express this view, and in proportion as the doctrine has become current amongst {356} anatomists, the parts of vertebræ have been described by terms of a degree of generality which admit of such an interpretation. And here, also, Mr. Owen has proposed a terminology for the parts of the vertebræ, which seems to convey more systematically and comprehensively than those of preceding writers the truths to which they have been tending. Each vertebra is composed of a _centrum_, _neurapophysis_, _parapophysis_, _pleurapophysis_, _hæmaphysis_, _neural spine_ and _hæmal spine_, with certain exogenous parts. The opinion that the head, as well as the other parts of the frame of vertebrates, is composed of vertebræ, is now generally accepted among philosophical anatomists. In the _History_ (_Hist. I. S._ b. xvii. c. 7, sect. 1), I have mentioned this opinion as proposed by some writers; and I have stated that Oken, in 1807 published a 'Program' _On the signification of the bones of the Skull_, in which he maintained, that these bones are equivalent to four vertebræ: while Meckel, Spix, and Geoffroy took views somewhat different. Cuvier and Agassiz opposed this doctrine, but Mr. Owen has in his _Archetype and Homologies of the Vertebrate Skeleton_ (1848), accepted the views of Oken, and argued at length against the objections of Cuvier, and also those of Mr. Agassiz. As I have noted in the last edition of the _History of the Inductive Sciences_ (b. xvii. c. 7), he gives a Table in which the Bones of the Head are resolved into four vertebræ, which he terms the Occipital, Parietal, Frontal and Nasal Vertebræ respectively: the neural arches of which agree with what Oken called the Ear-vertebra, the Jaw-vertebra, the Eye-vertebra, and the Nose-vertebra.