An anatomical study was performed to gain a better understanding of the pathogenesis of eyebrow ptosis. Through cadaver dissection, we sought to establish the anatomy of the normal eyebrow, to determine why the temporal part of the eyebrow becomes ptotic earlier than the medial portion, and to locate precisely the regional nerves and vessels to aid the eyebrow surgeon. a fat-pad exists beneath the eyebrow. Dense attachments on the underside of the eyebrow fat-pad secure the eyebrow to the supraorbital ridge. Because the supraorbital ridge extends only over the medial one half to two thirds of the orbit, the lateral part of the eyebrow lacks deep support and droops with the frontal skin and muscle relaxation seen in age. Vertical lateral orbicularis fibers are consistently seen in the cadaver. Because of their location, they may play a role in producing "laugh lines."