1845 appeared his "Odontography," a very important work, founded on microscopic examinations, containing descriptions and drawings of the structure of the teeth of every class of animals. His "Lectures on Comparative Anatomy and Physiology" were published between 1843 and 1846. His great work on the "Archetype and Homologies of the Vertebrate Skeleton" was the fruit of twenty-one years of study of the subject, and presented a revision of Cuvier's conclusions in the direction of recognizing a greater conformity to type than his illustrious predecessor had been willing to admit. In forwarding a copy of this work to Professor Silliman, of Yale College, Professor Owen wrote, in 1846: "You may remember the condition in which this philosophical department of anatomy was left by the great Cuvier and Geoff roy, and the discussions which unhappily tended to sever those estimable men in the latter period of their lives. The result was the formation of two schools, or parties, in the French world of anatomy, and subsequently the facts and arguments bearing upon these transcendental questions have been viewed in Paris through the prism of such party feeling. The chief and most cherished labor and reflections of many past years have been devoted by me to the acquisition of such truth as might lie at the bottom of the well into which this philosophy of anatomy seemed to have sunk after the departure of the great luminaries of the Jardin des Plantes."
In this work, and one on "The Nature of Limbs," that appeared after it, Professor Owen developed the idea of Oken, that the typical form of development in the higher mammals is the vertebra. In another work, "On Parthenogenesis," he introduced a term, which has since come into general use, to describe a most curious and interesting phenomenon in reproduction.
A very important division of Professor Owen's investigations is his work relating to the apteryx, and other fossil gigantic birds of New Zealand, concerning which he presented numerous carefully elaborated papers to the Royal and Zoölogical Societies. The successful restoration of one of these birds, from the few parts first found, was regarded by him as affording a vindication of Cuvier's principle, that the entire animal may be reconstructed from a single bone, or articular facet of a bone. By other applications of this principle to more or less complete fossil remains he was able to restore many remarkable forms of extinct animals from the fossil fragments brought home by Darwin from South America. He carried on valuable studies on the sloths from the same region, among which was the mylodon, and described the gigantic extinct marsupials of Australia. Turning his attention to the fossil beds at home, he published memoirs on the chelonia of the Purbeck lime-stones and Wealden clays, and the reptiles of the London clay and the cretaceous formations, and a monograph of the British fossil mammalia. Among his later studies in the field of fossil anatomy is his reconstruction of the curious long-tailed bird from Solenhofen, the Archeopteryx.