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Abstract
Two rhabdomyosarcomas of the orbit, a differentiated type and an embryonal type, were studied with the electron microscope. The differentiated type contained cytoplasmic aggregates of actomyosin filaments intermingled with clusters of RNP particles. The close morphologic resemblance of cells in this tumor to normal embryonic muscle cells was noted.
The embryonal rhabdomyosarcoma contained cytoplasmic clusters of RNP particles, nonspecific fine filaments, and large vesicles. No typical actomyosin filaments were seen.