Lectures on the comparative anatomy and physiology of the vertebrate animals : delivered at the Royal College of Surgeons of England, in 1844 and 1846. Part 1 Fishes / by Richard Owen.

  • Owen, Richard, 1804-1892.
Date:
1846
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Licence: Public Domain Mark

Credit: Lectures on the comparative anatomy and physiology of the vertebrate animals : delivered at the Royal College of Surgeons of England, in 1844 and 1846. Part 1 Fishes / by Richard Owen. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    62/344 (page 46)
    LECTUIiE 111, to establish three types of vertebraj. which may be eharacterised by the form of the articular ends of the centrum, as the “ biconcave,” the “ concavo-convex,” and the “ flattened” types, respectively dis- tinguishing, as a general rule, Fishes, air-breathing Ovipara, and Mammals. The least perfect form of a vertebra is that in fishes, though it often seems the most complex, from the intercalation of bones of the dermal system, and Geoffrey (ii. p. 119.)* was unfortunate in taking a fish’s vertebra, with this extrinsic complication, as the perfect type of that primary segment of the myelencephalous ske- leton. Two of the autogenous elements, the “ hasmapophyses,” for example, are not developed till we reach the Eeptilia : in fishes they are represented by the “ parapophyses” or lower transverse pro- cesses. Before entering, however, upon the special osteology of the class Pisces, it will be necessary to explain the sense in which the terms of groups or divisions of the class are used in these Lectures, in reference to their anatomical characters. Cuvier (xxiv. ii. p. 128.) primarily divides the class, according to the nature of their endo-skeleton, into Pisces ossei, and Pisces cartilaginei; but the latter group includes species of widely different grades of organisation, and in the “ Tables of Classification” exhibited in my first course of Lectures in this Theatre in 1837,1 separated the Lampreys, Myxinoids, and Lancelets, under the name “ Dermopteri, from the rest of the Chondropterygii of Cuvier, making these the highest, and those the lowest order of fishes, f M. Agassiz, with views enlarged by a survey of the extinct members of the class, divided the Pisces, by characters taken from the exo-skeleton, into four primary groups j viz. Plaeoidei, Ganoidei, Cyeloidei, and Ctenoidei. The fishes of the Placoid order are characterised by having the skin covered irregularly with plates of hard osseous matter, some- times of large size, and sometimes reduced to small points, as where they form the shagreen on the skin of many sharks and the prickly tubercles on the skin of most rays. This order comprehends all the * This ingenioHS anatomist was thus driven to as arbitrary assumptions of mu- tations of place, and to as far-fetched analogies, in reference to the supposed ele- mentary parts of the vertebra, as in his attempt to exemplify the homologies of the cephalic division of the endo-skeleton of the higher Vertebrata, by the combined bones of the exo- and endo-skeleton, which constitute the complex skull in I^isllGSj + The distinguished naturalist, C. L. Bonaparte, Prince of Canino, has also founded a distinct order for the Cyclostomous Chondroptcrygians of Cuvier, under the name of “ Marsipo-branchii,” which well applies to the Lampreys and Myxi- noids.— Selachorum Tabula Analijiica, 1838.