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Show 1904.] OSTEOLOGY OF THE ELOPIDSE AND ALBULIDJi:. 57 this will apply even in cases where the combined bone has sunk inwards and no longer presents itself as a superficial bone of the skull; as, for instance, the prefrontals and postfrontals of Arapaima and Osteoglossum, in which genera so many of the dermal bones are still dermal in position. Even if in these latter cases it be proved by histological investigation that the bone is a pure cartilage-bone, the argument is not the less sound. The ossification in the cartilage owed its origin phylogenetically to a predisposing dermal ossification which now no longer appears in ontogeny. The terms parethmoid, sphenotic, and pterotic are, therefore, redundant; and if the occasion arises for discriminating the two parts of the prefrontal, postfrontal, and squamosal, they should be distinguished by the terms ectosteal and endosteal. This practice has hitherto been followed, more or less, in the case of the articular and palatine bones. The two constituents of the palatine of Amico, for instance, are called exosteal and endosteal by Bridge (Journ. Anat. and Phys. xi. 4,1877, p. 616), while Allis (Journ. Morph, xii. 3, 1897) alludes to them as the dermopalatine and autopalatine, employing the prefixes introduced by van Wijhe (Med. Arch. f. Zool. v. 3, 1882). The question of ectosteal and endosteal ossification in fishes has already been discussed at some length by Vrolik (Nied. Arch. f. Zool. i. 3, 1873), Gegenbaur (Morph. Jahrb. iv. Suppl. 1878), Pouchet (Journ. Anat. et Phys. xiv. 1878), van Wijhe (I. c. 1882, p. 210 et seq.), and McMurrich (Proc. Can. Inst. ii. 3, 1884, p. 280 et seq.) ; and Schmid-Monnard (Zeitsehr. f. wiss. Zool. xxxix. 1883) has recorded some valuable observations on the mode of origin of such bones as the epiotic and squamosal in Teleostean fishes. More recently, Swinnerton (Quart. Journ. Micro. Sci. 1902, p. 531, footnote) has suggested the prefixes dermo- and chondro-, " the former being used for bones which are quite free of the cartilage, and the latter for those which involve cartilage, irrespective of the degree of ossification in this, or of the retention of dermal characters." This does not seem, however, to be a very satisfactory solution of the difficulty. Cranial Bones.-The meeting of the two parietal bones in the median line is, upon palaeontological grounds, a more primitive condition than the separation of these bones by the supraoccipital, no separation of the parietals occurring in pre-Cretaceous Isospon-dylous fishes (Smith Woodward, Yert. Palaeontology, 1898, p. 113). We have thus, to all appearances, one sound character by which to test the relative tendency towards specialisation among Teleostean fishes. But the possibility of a secondary approximation of superficial to the pterotic and inseparable from it, do not treat the terms postfrontal and sphenotic in the same way, on the ground that the term postfrontal " cannot be correctly applied to a mcmbranc-boiie in Fishes." W hy it cannot, they do not explain. . . . . . . . . . . |
