When Huxley took up the subject, the position was that the vertebral theory was in full possession of the field, under the auspices of Owen. Huxley began afresh from observed facts. The first object of his investigation was to settle once for all the question as to whether the skulls of all vertebrates were essentially modifications of the same type. He took in succession the skulls of man, sheep, bird, turtle, and carp, and showed that in all these there were to be distinguished the same four basi-cranial regions: the basi-occipital, basi-sphenoid, pre-sphenoid, and ethmoid. These were essentially identical with the centra of the four vertebræ of Oken. Similarly, he showed the composition of the lateral and dorsal walls, proving the essential identity of the structures involved and of their relations to the nerve exits in the great types he had chosen. In the series of lectures delivered before the College of Surgeons, he extended his observations to a much larger series of vertebrates, and substantially laid down the main lines of our knowledge of the skull. In two important respects his statements were not merely a codification of existing knowledge, but an important extension of it. He distinguished the different modes in which the jaws may be suspended to the skull, and established for these different kinds of suspensoria the names which have ever since been employed. He proved clearly what had been suggested by Oken, that the region of the ear is a lateral addition to the skull, and he distinguished in it three bones, his names for which have since become the common property of anatomists. Finally, he made it plain beyond any possible doubt that the skulls of all vertebrates were built upon a common plan.