[The fine structure of myotendinous and myo-epithelial junctions in the guinea pig tongue (author's transl)].

The insertion of muscle fibers in the subepithelial connective tissue layer of the guinea pig tongue was studied light and electron microscopically. Fibers of the tractus verticalis approach the epithelium penetrating the lamina propria, both the reticular and papillar layer. Terminating muscle fibers split up and form branching finger-like cytoplasmic processes. The myotendinous junctions of such terminal processes fine structurally correspond to myotendinous junctions generally observed in skeletal or smooth muscles. The entire brush-like formation, however, is more far-reaching and highly differentiated. Filament bundles (spine-like profiles) originate from the plasmalemma and extend to the lamina densa of the basal lamina, especially in those regions where actin filaments are attached to the plasmalemma. Microfibrils (10 to 12 nm diameter) reach the lamina densa of the basal lamina. They form bundles which are continuous with fibrotubular strands of elaunin fibers and elastic fiber microfibrils. Furthermore, microfibrils are interwoven with collagen fibrils.