. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 106 CCJMPARATIVE ANATOMY previously put forward the view that the arches and fins correspond to meta- morphosed gill-arches and rays : he supposed that one ray came to exceed the others in size, and that the others then gradually became attached to it instead of to the arch, the result bemg a biserial form of fin (" a/i-chiptery-, (j'in)ii, "') which is most nearly retained in Ceratodus (Fig. 101 and p. 124). Pectoral Arch. Fishes and Dipnoans.—Paired fins and arches are wanting in the Cyclostomi. In the Elas
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 106 CCJMPARATIVE ANATOMY previously put forward the view that the arches and fins correspond to meta- morphosed gill-arches and rays : he supposed that one ray came to exceed the others in size, and that the others then gradually became attached to it instead of to the arch, the result bemg a biserial form of fin (" a/i-chiptery-, (j'in)ii, "') which is most nearly retained in Ceratodus (Fig. 101 and p. 124). Pectoral Arch. Fishes and Dipnoans.—Paired fins and arches are wanting in the Cyclostomi. In the Elasmobranchii and Holocephali the pectoral arch consists of a comparatively simple cartilaginous bar. Fig. 83.—Pectoral Arch and Fix of Hi-ptancliux. SB, SB^, pectoral arch, with a nerve aperture at XL ; Pr, J{s, Mt, the three basal elements of the fin—pro-, meso-, and metapterygiimi; Ra, cartilaginous fin-rays ; a, b, the main fin-ray, lying in the axis of the metapterygium ; +, single ray on the other side of the axis (indication of a biserial type) ; FS, horny rays, cut through. the two halves of which are united ventrally by cartilage or fibrous tissue (Fig. 83), and in embryos of Ganoids and Teleosts it has at first a similar structure. Later, however, in both the last-named groups, a row of bony structures arises in the perichondrium in this region; so that a secondary or bony pectoral arch may be distinguished from a primary or cartilaginous one, the latter becoming less marked in proportion to the development of the former (Fig. 84). The free extremity, or fin, is always connected with the hinder. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wiedersheim, Robert, 1848-1923; Parker, William Newton, 1857-1923. London, Macmillan
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
