. The Cambridge natural history. Zoology. 242 FISHES plate, produced in front into a long tapering epipubic process, and on each side of this into a forwardly inclined prepubic pro- cess. The hinder part of the plate bears two short processes for the basal cartilages of the pelvic fins. There is no trace, how- ever, of iliac processes. The Pectoral Fins.—The skeleton of the pectoral fins exhibits remarkable structural variations in different Elasmobranchs. In the existing members of the group two large basal cartilages, the propterygium and the mesopterygium, are formed by the concen- tration
. The Cambridge natural history. Zoology. 242 FISHES plate, produced in front into a long tapering epipubic process, and on each side of this into a forwardly inclined prepubic pro- cess. The hinder part of the plate bears two short processes for the basal cartilages of the pelvic fins. There is no trace, how- ever, of iliac processes. The Pectoral Fins.—The skeleton of the pectoral fins exhibits remarkable structural variations in different Elasmobranchs. In the existing members of the group two large basal cartilages, the propterygium and the mesopterygium, are formed by the concen- tration and fusion of the proximal portions of certain of the preaxial radialia, and they, with the metapterygium, articulate with the pectoral girdle; hence the fin is tribasal as well as uniserial (Figs. 141 and 146, A, B). In striking contrast to all otlier Elasmobranchs the pectoral fin of Cladoselache (Fig. 145, A) is far more primitive than in any other Fish. Each fin is supported by a distal series of slender, more or less parallel, mi- jointed, cartilaginous radialia, and basally by a similar series of shorter, stouter, and less numerous cartilages, which apparently were imbedded in the body- wall, the entire fin skeleton presenting a striking re- semblance to an isolated median fin in which the supporting radialia have concentrated by growth pressure, and their proximal portions have been reduced in number by partial ;*^ Pleuracanthus, on the other hand, had a biserial fin, the preaxial and postaxial radialia supporting fan-like clusters of horny fibres at their distal ends (Fig. 250). The broadly lobate pectoral fin of the existing Crossopterygii 1 Bashford Dean, Anat. Anz. xi. 1896, p. Fig. 145.—A, Pectoral fin, ami B, pelvic fin of Clctdoselache. (From Bashford Dean.). 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 perf
Size: 1355px × 1844px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
