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Myotubes in fetal muscle (photomicrographs)

Transverse sections of quadriceps femoris muscle of a 14-week human fetus (left) and a term neonate with X-linked myotubular myopathy (right). In the fetal muscle, both early and late myotubes are seen; the early fibers have scant cytoplasm whereas the late or mature myotubes have more abundant cytoplasm because of a larger number of myofibrils that form a cylinder around the central core of the fiber occupied by nuclei and organelles between nuclei. (Hematoxylin-eosin; x1000 and x400) (Used with permission. Sarnat HB. Myotubular myopathy: arrest of morphogenesis of myofibers associated with persistence of fetal vimentin and desmin. Four cases compared with fetal and neonatal muscle. Can J Neurol Sci 1990;17:109-23.)