OCR Text |
Show 278 LECTURE XIV. ON THE STRUCTURE OF THE VERTEBl~ATE SKULL. THE THEORY OF THE VERTEBRATE SKULL. IN the preceding Lectures I have, as far as possible, eonfined myself to a statmnent of matters of fact, and to the conclusions which immediately flow fron1 the application of a very simple method of interpretation to the facts. That method of interpretation is based upon the principle that, in any two skulls, those parts which are identical in their principal relations in the adult state, and in the mode in which they reach this state (or in their development) are corresponding, or homologous, parts, and need to be denominated by the same terms. By the application of this method it has been possible to demonstrate the existence of a fundamental unity of organization in all vertebrate skulls ; and, furthermore, to prove that all bony skulls, however much they Inay differ in appearance, are organized upon a common plan, no important bone existing in the highest vertebrate skull which is not recognisable in the lowest completely ossified cranium. The enunciation of these results alone is a " Theory of the Skull,'' but it is by no means what is commonly understood as the theory of the skull. For it will be observed that the statement just put forth confines itself to a simple generalization of the observed facts of cranial structure, and would be perfectly complete were the skull a self-subsistent structure, devoid of any connection with a trunk. On the other hand, that doctrine to which the title of "The rrheory of the Skull" is ordinarily applied, embraees not THl~ THEORY OF THE VERTEBRATE SKULL. 279 only s.uch a generalized statement of the facts of cranial structure as thiS, but adds a hypothesis respecting the relations of the skull to the spinal column. It assumes that the bony · (tl • • c cranium 1e ~artilagi~ous and n1embranous states of the cranium it usually Ignore~) Is composed of elements homologous with those which ente.r Into the s.t ructure of the spinal column·, t}1 at, I·n f:a c t , 1' t consi~ts. of modrfi~d vertebrm. And it is commonly conceived that It IS the doctrine of the unity of structure of the skull and of .the vertebr~l c.olumn, rather than the demonstration of the unity of organization of skulls, which is one of the chief glories of morphology. The assumptio~ that every skull repeats the organization of the'd t runk and consists of a certain number of modified ve ·t b. 1 · . . . r e ue, evi ~n~ y Imphes a belief 111 the unity of organization of skulls; but It IS to be caref~ll.y no~ed that the converse proposition does not hold good ; for It Js quite possible to hold that all skulls a d'fi · re mo 1 catwns of one fundamental plan, while wholly disbelieving that plan to be similar to the plan of a vertebral column .Looking broadly at the history of the theory of the skull (us~ng t.he ph1~ase in its widest sense), I note three great Jines of I~q.uuy whwh have brought that theory into its present cond1twn,-the first originated by Oken and Goethe·. th Recond, not originated, perhaps, but chiefly fostered and deve~ loped by Geoffroy .st. Hilaire and Cuvier; the third, originated, an~ almost exclusively worked out, by Reichert, Rathke, and then followers among the embryologists of Germany and England. . ~· I have united the names of Goethe and of Oken as the originators of the hypothesis of the vertebral structure of the skull, as a matter of equity, and to aid in redeeming a great ~a~e from undeserved obloquy; though, in strict technical JUSti?e, ~he claim of the one to priority lapsed through lack of pubhcat1on. Goet~e combined with a fervid creative genjus, which has placed him on a level with the greatest poets of all ages, so much. of observational acuteness and of intellectual precision as might have sufficed for the equipment of a well-reputed |