Abstract
Embryonic myogenesis and neurogenesis of human extraocular muscles (EOM) were studied by light and electron microscopy in a group of embryos and fetal specimens (6 to 24 weeks gestational age) (20 to 200 mm CR length).The earliest trace of EOM in humans have been reported at 7 mm (4 weeks) as a single undifferentiated mass of condensed paraxial mesoderm surrounding the optic vesicle. There is no separation between individual muscles. The distinction occurs before the 20 mm stage (6-7 weeks) when the 4 recti and the 2 obliques can be recognized(1). The oculomotor nerve can be identified as an elongation of the midbrain at 12.2 mm (5th week). The trochlear nerve appears between the 6th and 7th weeks and the abducens nerve is recognizable first at 31.3 mm (8th week). By the end of the 8th week, all the nerves had reached their respective muscles.
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