. The chordates. Chordata. Motor System—Muscles and Skeleton 93. Fig. 92. Diagrams showing budding of hypoglossal- and pectoral or fin muscles from trunk myotomes in an elasmobranch embryo. (A) Lateral view after Braus. (2-6) Visceral arches. (B) Cross section in region of pectoral fin-fold. (Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) toral and pelvic fins are developed from mesoderm which grows out from several myotomes adjacent to the base of the "limb-bud" (Fig. 92). Presumably the appendicular muscles of primitive vertebrates were
. The chordates. Chordata. Motor System—Muscles and Skeleton 93. Fig. 92. Diagrams showing budding of hypoglossal- and pectoral or fin muscles from trunk myotomes in an elasmobranch embryo. (A) Lateral view after Braus. (2-6) Visceral arches. (B) Cross section in region of pectoral fin-fold. (Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) toral and pelvic fins are developed from mesoderm which grows out from several myotomes adjacent to the base of the "limb-bud" (Fig. 92). Presumably the appendicular muscles of primitive vertebrates were derived from segmented mesoderm. There is some doubt, how- ever, as to the exact source of the appendicular mesoderm in the tetrapods. It is possible that it may be derived in part from the unseg- mented ventrolateral mesoderm of the embryo—, from the somato- pleure which otherwise becomes the parietal peritoneum (Fig. 90, p). The muscles of a lateral fin of a fish are few and simple (Fig. 93). These fins are ordinarily used not for propulsion but for steering and balancing. While the skeletal rays which stiffen the fin may be jointed, the protruding part of the fin works as a whole in relation to its basal skeleton or girdle, which is embedded in the muscle of the body-wall. A muscle extending from the dorsal part of the girdle onto the dorsal surface of the fin serves as an elevator (or extensor) of the fin, its action LATERAL UNE TRAPEZIUS M CONSTRICTORS OF GILLS SPIRACLE. 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 Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : Blakiston
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