| OCR Text |
Show 1869.] ON THE MALLEUS AND THE INCUS OF THE MAMMALIA. 391 6. On the Representatives of the Malleus and the Incus of the Mammalia in the other Vertebrata. By T. H. HUXLEY, F.R.S. In the course of the last two years, Professor Peters has contributed to the ' Monatsberichte' of the Berlin Academy a series of papers in which he advocates what I may term, for brevity's sake, the " Oke-nian " doctrine of the homologies of the ossicula auditus of Mammals and of the quadrate bone of the other Vertebrata. According to this view, the ossicula auditus of Mammalia are completely represented by the auditory columella in other Vertebrata, while the tympanic is the homologue of the quadrate bone. In supporting it, Professor Peters necessarily argues against the doctrine originally put forward by Reichert, and subsequently adopted by myself, that the auditory columella of the lower Vertebrata does not answer to all the ossicula auditus of the Mammalia, but only to the stapes-the incus being represented by the quadrate bone, the malleus by the articular; while the homologue of the tympanic is only to be found occasionally, in ossifications of the fibrous frame of the tympanic membrane. In the first two papers of the series, Prof. Peters bases his argumentation upon the anatomical relations of the lower jaw and the tympanic bone in the Marsupialia and Monotremata ; but as these facts are, undoubtedly, capable of being interpreted as well upon the Reichertian as upon the Okenian hypothesis, I did not conceive it necessary to enter, at present, upon any discussion of them. On the 19th November, 1868, however, Prof. Peters made a third communication to the Berlin Academy, " Upon the Auditory Ossicles aud the Meckelian Cartilage in Crocodiles," which was followed on the 7th January, 1869, by a fourth, " Upon the Auditory Ossicles of Chelonia, Lizards, and Ophidia, as well as upon the cavities of the Lower Jaw of the Crocodile," which seemed to me to demand immediate attention ; for the quadrate bone of the Crocodile cannot possibly represent either the incus, or the malleus, if the statement of anatomical facts made by Prof. Peters is correct. I therefore proceeded to the verification of his descriptions with much interest and a little anxiety; but after dissecting the skulls of several young Crocodiles with great care, I must declare m y conviction that Prof. Peters is in error as to the facts, and, therefore, that the argument he bases upon them falls to the ground. The able anatomist Stannius first drew attention to the pneuma-ticity of the lower jaw in the Crocodile, in the following terms :- "The os articulare of the lower jaw is distinguished by its pneu-maticity ; its great hollow cells communicate, by a canal which lies at the back of the os tympanicum [quadratum], with the air-chambers of the cranial bones. The lowest part of the canal in question forms a groove in the dry skull. This, in the fresh skull, is converted into a soft tube; and a free membranous tube leads into a hole placed on |
