. A manual of zoology. XII PHYLUM CHORDATA 373 number of slender homy fibres of dermal origin. In the smaller median fins there may be an elongated rod of carti- lage constituting the skeleton, or cartilage may be entirely absent. In the pectoral fin (Fig. 225) the fin-rays are supported on three basal cartilages articulating with the pectoral arch. The latter is a strong hoop of cartilage in- complete dorsally, situated immediately behind the last of rljf. Fig. 22^. —Ventral view of pectoral arch of ScyIlium with right pectoral fin. The pectoral arch is divisible into dorsal {pet. g) and vent
. A manual of zoology. XII PHYLUM CHORDATA 373 number of slender homy fibres of dermal origin. In the smaller median fins there may be an elongated rod of carti- lage constituting the skeleton, or cartilage may be entirely absent. In the pectoral fin (Fig. 225) the fin-rays are supported on three basal cartilages articulating with the pectoral arch. The latter is a strong hoop of cartilage in- complete dorsally, situated immediately behind the last of rljf. Fig. 22^. —Ventral view of pectoral arch of ScyIlium with right pectoral fin. The pectoral arch is divisible into dorsal {pet. g) and ventral \ pet. g) portions, separated bv the articular facets {) for the fin. The pectoral fin is formed of three basal cartilages 'bs. 7-5) and numerous radials irad): its free edge is supported by dermal rays , r). (Modified from .Marshall and Hurst.) the branchial arches. It consists of a dorsal, or scapular, (pet. g) and a ventral, or coracoid, portion ('), the coracoid portions of opposite sides being completely con- tinuous across the middle line, while the scapular are sepa- rated by a wide gap in which the spinal column lies. Between the two portions are the three articular surfaces for the three basal cartilages. The three basal cartilages of. 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 Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Haswell, William A. (William Aitcheson), 1854-1925. New York, The Macmillan Company; London, Macmillan & Co. ,Ltd.
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