. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 110 COMPARATIVE AKATOMY become segmented off from the basal cartilage (hasi- or metaptery- gium) of the free fin. In some cases even this segmentation does not take place, and thus the pelvis remains undifferentiated. This simple condition is also met Avith in the ancient forms Pleura- canthus and Xenacanthus, and is essentially retained in Lepi- dosteus, Amia, and the Teleostei (Fig. 87). In Polypterus, which most nearly resembles the Devonian Crossopterygii, the pelvis shows some advance on that of Sturgeons. Owing,
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 110 COMPARATIVE AKATOMY become segmented off from the basal cartilage (hasi- or metaptery- gium) of the free fin. In some cases even this segmentation does not take place, and thus the pelvis remains undifferentiated. This simple condition is also met Avith in the ancient forms Pleura- canthus and Xenacanthus, and is essentially retained in Lepi- dosteus, Amia, and the Teleostei (Fig. 87). In Polypterus, which most nearly resembles the Devonian Crossopterygii, the pelvis shows some advance on that of Sturgeons. Owing, doubtless, to the necessity of a firmer connec- tion of the fin with the body-wall, the two pelvic plates become X t Ba^^ Bas / P Bas^. Fig, 87.âDiagrams illustrating the Phylogexy of the PELVih. A, PleuracanlhiiKâthe pelvis is here undifferentiated tt; B, Scaphirhynrluii' cataphractlis; C, bichir; D, Nectm-iis {Menobranr]ui>i). Bas^. basipterygium ; Ap, its cartilaginous apophysis ; P, pehns ; Bad, radii ; Fo, obturator foramen. united together in the mid-ventral line (Fig. 87, C) : but even here the basipterygium may remain in continuity with the pelvic plate on one or both sides. In spite, however, of the rudimentary chai-acter of the pelvis of Polypterus, the essential form of that of the Dipnoi and Amphibia is already sketched out. The pelvis of the Elasmobranchii and Holocephali indicates that they early branched off from the ancestral stock. Instead of a small and narrow pelvic plate more or less elongated antero- posteriorly, the pelvis forms a transverse bar of considerable extent, developed in connection with the basipterygium (Fig. 82) â. 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
