. The elasmobranch fishes. Chondrichthyes. 96 THE ELASMOBRANCH FISHES MUSCULATURE OF ELASMOBRANCHS IN GENERAL. In a consideration of the musculature of Elasmobranelis in general we may first notice the primitive segments or somites which in the eml)ryo are ar- ranged in series from the region back of the ear to the tip of the tail. A trans- verse section through the trunk (tig. 97) shows the somite to be made up of an outer and an inner layer between which is a central cavity or myocoele (mc). The outer layer produces the dermatome or cuticle plate (dt.) and the inner layer is divided into an
. The elasmobranch fishes. Chondrichthyes. 96 THE ELASMOBRANCH FISHES MUSCULATURE OF ELASMOBRANCHS IN GENERAL. In a consideration of the musculature of Elasmobranelis in general we may first notice the primitive segments or somites which in the eml)ryo are ar- ranged in series from the region back of the ear to the tip of the tail. A trans- verse section through the trunk (tig. 97) shows the somite to be made up of an outer and an inner layer between which is a central cavity or myocoele (mc). The outer layer produces the dermatome or cuticle plate (dt.) and the inner layer is divided into an upper myotome i^uy.) and a lower sclerotome (scl.). These two layers extend ventrally as the lateral plate and inclose between them the body cavity or coelom (c). For a time in the Elasmobranchs these two cavities are continuous, but later they are sepa- rated by the fusion of the two layers giving a somite dorsally independent of the lateral plate (seep. 298, fig. 257). The sclerotome of the somite, as we have seen in Chapter III, produces the elements of the verte- bral column, while the dermatome gives rise to those connective tissue fibers characteristic of the corium and sometimes may also give rise to a part of the muscle tissue. The myotome, however, produces the mass of skeletal muscle. The lateral plates which enclose the coelom are divided into an inner splanchnic layer (spl.) which produces the muscular layer of the digestive tract; and a somatic layer (so.) which thins out ventrally, forms the peritoneal lining of the body cavity, and gives rise to connective tissue cells. The cells of the myotome, the myoblasts, elongate and attach themselves both anteriorly and posteriorly to the connective tissue septa (myosepta) sep- arating somites (fig. 98). Such a muscle cell or fiber furthermore becomes differentiated into longitudinal fibrils and is crossed by a series of transverse stripes or bands. In the body of the adult Elasmobranch the fibers generally retain the simi
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