. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 44 OEKEBAL PAET. In the first case we have to do with flat, spindle-shaped, or band- shaped elongated cells, and with layers of su:-h cells. They react slowly to nervous stimuli; they enter the condition of contraction gradually, and remain contracted for some time. The contractile substance appears for the most part to be homogeneous;, but it is sometimes longitudinally striated. /. The smooth muscles have the widest distribution amongst the Invertebrata; but they are also found in vertebrates, in
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 44 OEKEBAL PAET. In the first case we have to do with flat, spindle-shaped, or band- shaped elongated cells, and with layers of su:-h cells. They react slowly to nervous stimuli; they enter the condition of contraction gradually, and remain contracted for some time. The contractile substance appears for the most part to be homogeneous;, but it is sometimes longitudinally striated. /. The smooth muscles have the widest distribution amongst the Invertebrata; but they are also found in vertebrates, in the walls of numerous organs (vessels, ducts of glands, intestinal wall) (fig. 35). Cross-striped muscle consists of cells, more frequently of multi- nucleated so-called primitive bun- dles. It is characterised by the partial or complete transforma- tion of its protoplasm into a cross- h laiiiiugj tei^i^ Fig. 3G.—a, I'rimitivefibre. muscle fibre (primitive muscle bundle) of Lscerta with uerve termination. Fig. 35.—a, smooth muscle fibres isolated, b, piece of an artery (after Frey) ; 1, outer connective tissue layer; 2, the middle ] jyer formed of smooth muscle fibres; 3, non-nu- cleated inner layer. striped substance, consisting of special doubly refracting elements (sarcous elements) connected to- gether by a simply refracting inter- mediate substance (fig. 36, a, b). Physiologically, this form of mus- cular tissue is characterised by the energetic and considerable contraction which immediately follows its excitation, a property which renders it especially suitable for the carrying out of powerful movements (muscles of vertebrate skeleton). In the simplest cases the cross-striped fibrillte are produced by the deeper parts of the myoblasts, which form a continuous flat surface epithelivim (muscle epithelium) above the layer of delicate fibres ( and Siphonophora) (fig. 34 b). In the higher animals they. Please note that these images are extracted fro
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
