The theory, then, which had dropped stillborn from Goethe, but which Oken developed, was simply that the skull consisted of a series of expanded vertebræ. Each vertebra consists of a basal piece or centrum, the anterior and posterior faces of which are closely applied to the face of an adjoining vertebra, and of a bony arch or ring which encloses and protects the nervous cord. Oken supposed that there were four such vertebræ in the skull, the centra being firmly fused and the arches expanded to form the dome of the skull. Quite correctly, he divided the skull into four regions, corresponding to what he called an ear vertebra, at the back, through which the auditory nerves passed; a jaw vertebra, in the sphenoidal region, through which the nerves to the jaws passed; an eye vertebra in front, pierced by the optic nerves, and again in front a nose vertebra, the existence of which he doubted at first. Quite rightly, he discriminated between the ordinary bones of the skull and the special structures surrounding the inner ear which he declared to be additions derived from another source. So far it cannot be doubted that the vertebral theory made a distinct advance in our knowledge of the skull. It was to a certain extent, however, thrown into disrepute by various fantastic theories with which Oken surrounded it. Later on, Cuvier removed from it these wilder excrescences, and amplified the basis of observation upon which the underlying theory of the unity of type of the skull throughout the vertebrates was based. Cuvier, however, came to reject the theory, except so far as it applied to the posterior or occipital segment of the skull. Later on, Owen resuscitated the theory, first throwing doubt on the merit of Goethe, and then suggesting that Oken, instead of relying on the observed facts, had deduced the whole theory from his own imagination. Owen, although he made no new contribution to fact or theory in this matter, practically claimed the whole credit of it as a scientific hypothesis.