. The elasmobranch fishes . Muscles op the Fins Fig. 111. Development of the muscles to the pectoral fin, Acanthias. (From Erik Miiller.) 1-33, muscle buds; I-XII, nerves. In Elasmobranchs the muscles of the paired fins arise in the embryo as buds from the ventral downgrowth of the myotome. Varying numbers of these buds take part in the formation of the fins in different species of Elasmobranchs. After the dorsal somite is separated off from the lateral plates its myotome grows rapidly both dorsally and ventrally. As the ventral downgrowth passes the fin area it gives off the muscle buds as la
. The elasmobranch fishes . Muscles op the Fins Fig. 111. Development of the muscles to the pectoral fin, Acanthias. (From Erik Miiller.) 1-33, muscle buds; I-XII, nerves. In Elasmobranchs the muscles of the paired fins arise in the embryo as buds from the ventral downgrowth of the myotome. Varying numbers of these buds take part in the formation of the fins in different species of Elasmobranchs. After the dorsal somite is separated off from the lateral plates its myotome grows rapidly both dorsally and ventrally. As the ventral downgrowth passes the fin area it gives off the muscle buds as lateral growths. The muscle bud separates into an anterior and a posterior primary bud, each of which in turn divides into an upper and a lower secondary bud so that from one myo- tome four buds arise. The two of these l)uds which are dorsal in position go to make up dorsal fin muscles, while the two ventral in position compose the ventral musculature of the fin (fig. 111).
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