Twenty-two normal lower eyelids were studied microscopically to examine the normal anatomy of the lower eyelid retractors. Eight lower eyelid specimens from patients with involutional entropion and five from patients with involutional ectropion were studied also. In the normal eyelids, the inferior tarsal muscle consisted of scattered smooth-muscle fibers and did not insert on the tarsus. The orbital septum fused with the capsulopalpebral fascia 5 mm beneath the lower tarsal border to form a single, complex fascial layer. In the involutional entropion and ectropion cases, the fused capsulopalpebral fascia-orbital septum complex was attached to the tarsus in all specimens. The first identifiable smooth-muscle strands of the inferior tarsal muscle averaged 3.9 mm from the lower tarsal border in entropion cases, 4.5 mm in ectropion cases, and 2.5 mm in the normal eyelids.