On the archetype and homologies of the vertebrate skeleton / by Richard Owen.

  • Richard Owen
Date:
1848
Catalogue details

Licence: Public Domain Mark

Credit: On the archetype and homologies of the vertebrate skeleton / by Richard Owen. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    I: Cuvier describes the posterior ami superior expanded and diverging plates the prefrontals as “ la lame cribrcuse de 1 ethinoide: the coalesced part ' rniiii the septum, he ascribes to the vomer*. Dr, Kbstlin j, also, who i gards the ethmoid as no proper bone of the skull, but oidy an ossified ^n of sense, yet describes, after the anthropotomists, the coalesced pre- ' lutals as the cribriform and azygos processes of the ethmoid (‘Siebplatte ■ d ‘ Scheidewand des Siebbeins,’ pp. 85. 89) in cetacea which have no ■;ian of smell. In a young balmnoptera, in which tlie frontals, the vomer i d the nasals were ossified, I find the prefrontals as two cartilaginous plates, tending from the nasals above to the groove of the vomer below. In the iiinatee^the essential parts of the prefrontals which close the cranial cavity teriorly, and give exit to the olfactory nerves, are thick and unusually ' 'panded. But in no mammal do these parts, with their continuation, the •' i.iiuina perpendicularis,’ which, as the coalesced neurapophysial plates of sfrontals, brings the vomer below in connection with the nasals above, ■ i-er undergo such modifications as to obliterate their true and essential ho- i dogical characters. :In proceeding next to consider the special homologies of the bones of the ■ ;h closed by the premaxillaries (22) and constituting the ‘ upper jaw,’ I ’ raimence with the palatines (20), because they form, throughout the verte- ;ate series, the most constant medium of suspension of that arch to the ^ titerior cranial segment formed by the vomer, prefrontals and nasal. This a hicret affinity,’ as Goethe would have termed it, before the knowledge of ;: general type had revealed its nature, is manifested by the process of the i Uatine in man, which creeps up, as it were, into the orbit to effect its wonted - ion with the prefrontal, to that part of the bone, viz. of which Cuvier had - ;ijognised the homologue in his ‘ ethmoide’of the bird!. It is the very '.nstancy, indeed, of these and other connections which has exempted the I iiatine from the different determinations and denominations attached to ■ -ler bones, and which renders further discussion of its special homology i .necessary here. - IPassing over, for the same reason, the maxillary (21) and premaxillary (22), i ;d referring to the excellent treatise by Dr. Kostlin§ for the grounds of = determination of the ‘pterygoid’ (24), I proceed to notice other bones i.iich, diverging from the maxillary arch, serve to give it additional fixation ■ :d strength in the air-breathing vertebrates. The first of these is the malar 1: ne (fig. 11, 2c), the homology of which has been traced without difference J opinion throughout the mammalian class; where, however, the inconstancy ; its proportions, number of connections, and very existence, is sufficient to ;dicate its comparative unimportance as an element of the maxillary arch, is absent in many insectivores (^Centetes, Echinops, Sorex'): it has not ;;' en detected as a distinct bone in the zygomatic arch in the monotremes, on count perhaps of its early coalescence, as in birds, with the maxillary i .'g. 12, 21, 2o); \n Myrmecophaga gigantea and Manis, it projects back- i trds, as a styliform appendage, from the maxillary, but does not attain the uamosal; whilst in the sloths and their extinct congeners the gigantic , --gatherioids, the malar presents its maximum of development and complex- j ’,!• In the JJelphinidce, again, the malar is much reduced : its slightly ex- nded maxillary end forms part of the orbit and joins the frontal; the rest I tending backwards, as a very slender style, beneath the orbit to the squa- ' * Ossem. Foss. v. pt. i. pi. xxvii. fig. 3, h. t Der Ban des Kndchernen Kopfes, p. 11. t See the passage above ipioted from the ‘ Lemons d’Anat. Comp.’ ii. p. 580. § 0]!. cil. p. 328. II Dcscriiitioii of the Myludon rohuatus, Ito, p. 19.