During the past six years we have studied 116 biopsy specimens of the levator muscle from patients with ptosis. Our purpose has been threefold: first, to ascertain the histological nature of the levator muscle in congenital and acquired ptosis; second, to learn whether the histological structure of the levator in these cases affected the final results of resection of the levator muscle, and, third, to elucidate the cause of congenital ptosis. REPORTED PATHOLOGICAL FINDINGS IN CONGENITAL PTOSIS Only a few gross anatomical and histological reports on the structure of the levator muscle in congenital ptosis are available. For example, Heuck1 (1879) removed post mortem the orbits of an 18-year-old youth with complete congenital ptosis and demonstrated an atrophic levator, only 2 mm. wide, in the right orbit and complete absence of the levator in the left. In addition, both superior rectus muscles were very thin and almost nonexistent. Bach