I. The Croonian Lecture.—On the theory of the vertebrate skull

The necessity of discussing so great a subject as the Theory of the Vertebrate Skull in the small space of time allotted by custom to a lecture, has its advantages as well as its drawbacks. As, on the present occasion, I shall suffer greatly from the disadvantages of the limitation, I will, with your permission, avail myself to the uttermost of its benefits. It will be necessary for me to assume much that I would rather demonstrate, to suppose known much that I would rather set forth and explain at length; but on the other hand, I may consider myself excused from entering largely either into the history of the subject, or into lengthy and controversial criticisms upon the views which are, or have been, held by others. The biological science of the last half-century is honourably distinguished from that of preceding epochs, by the constantly increasing prominence of the idea, that a community of plan is discernible amidst the manifold diversities of organic structure. That there is nothing really aberrant in nature; that the most widely different organisms are connected by a hidden bond; that an apparently new and isolated structure will prove, when its characters are thoroughly sifted, to be only a modification of something which existed before,—are propositions which are gradually assuming the position of articles of faith in the mind of the investigators of animated nature, and are directly, or by implication, admitted among the axioms of natural history.