Elements of comparative anatomy / by Carl Gegenbaur ; translated by F. Jeffrey Bell ; the translation revised and a preface written by E. Ray Lankester.
- Carl Gegenbaur
- Date:
- 1878
Licence: Public Domain Mark
Credit: Elements of comparative anatomy / by Carl Gegenbaur ; translated by F. Jeffrey Bell ; the translation revised and a preface written by E. Ray Lankester. Source: Wellcome Collection.
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![been derived from tlie gradual shifting, atrophy, hypertrophy, and con- crescence of primitively similar cartilaginous rods, which formed a series on each side of the body, identical in character with the primitive median dorsal series. According to this view, the archipterygium of Professor Gegenbaur is not antecedent to, but is derived from the type of fin found in Elasmobranchs. (See also on this subject, Huxley, On Ceratodus^ Proc. Zool. Soc. vol 1876, p. 24.) Relation of the Malleus and Incus to the Mandibular and Hyoid Arches.—Investigations directed to the development of the skull led Professor Huxley some years since to adopt the conclusion of Reichert and of GooDSiR, that the small bones of the Mammals' tympanic cavity were derived from the upper ends of the anterior visceral arches. At first it appeared probable that the malleus and incus were both derived from the upper end of the cartilaginous mandibular arch, the lower part forming Meckel's cartilage. This led to the suggestion that the malleus corresponds to the articulare of the lower jaw of other Vertebrata, whilst the incus was considered to be the representative of the quadratum, since it articulates Avitli the malleus just as the quadratum does with the articulare (Croonian Lecture On the Theory of the Vertebrate Skull/' Proc. Royal Society, voL ix. p. 398). Further investigation led Professor Huxley to a modification of his views. The embryological evidence is not quite complete, but the relations of the parts in question in the developing Frog, in certain Lizards, and in Mam- malia, have led him to the conclusion { Manual of Vertebrate Anatomy, p. 85, 1871) that whilst the malleus is formed from the uppermost extreuiity of the mandibular arch, and therefore represents, not articulare, but quad- ratum, the incus is developed from the uppermost extremity of the second or hyoid arch, and corres]3onds to the hyomandibular of fishes. The stapes is also developed from the upper portion of the hyoid arch, just below the incus. The incus may therefore be spoken of as the supra-stapedial portion of the hyoid arch, and in certain Vertebrata it exists as a mere cartilaginous supra-stapedial rudiment. These views in their later form have not been adopted by Professor Gegenbaur. He observes (§ 402) that the homologies of the ossicula auditus of the various classes of Vertebrata have not yet been satisfactorily determined. In § 352 he maintains the earlier determination of the homo- logy of the mammalian malleus with the articulare of other Vertebrates. Concerning the homologies of the incus and the stapes, he considers it advisable, in the present state of knowledge, to make no statement. The student is advised of these diff'erences of interpretation of structural fact, in order that he may the more carefully make himself acquainted from original sources with the details of development, relation to nerves, and other features of the parts under discussion. J^'omenclature of the Lobes of the Brain in Fishes.—In the earlier editions of the present work, Professor Gegenbaur, led by the result](https://iiif.wellcomecollection.org/image/b20417202_0018.jp2/full/800%2C/0/default.jpg)
