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Abstract
The fine structure of neuromuscular junctions in extraocular muscles obtained from 10 myasthenic patients was investigated. In the Felder-struktur muscle fibers, all of the junctions appeared normal in their structure, although the number studied was limited. In the Fibrillen-struktur, approximately one fourth of the junctions studied showed structural alterations of various types. The terminal axons were frequently elongated, although their synaptic vesicles and mitochondria appeared normal in structure and number. The primary synaptic cleft was occasionally dilated to form a cystic enlargement. The junctional folds often increased in number, reaching more than 20. An extensive elongation and ramification of the infolds was occasionally observed. Sponge-form structures, not described in previous literature, were encountered in the interior of a few muscle fibers. They seemed to have resulted from an extensive elongation and ramification of the junctional folds.