Scanning electron microscopic studies of the zonular apparatus in 10 human and 17 monkey eyes revealed two functionally different sets of zonular fibers: the "main fiber" and the "tension fiber" system. The two systems are connected, forming a broad, sagittally oriented "zonular plexus" within the pars plicata of the ciliary body. The zonular plexus is attached to the ciliary epithelium by the tension fibers, which leave the main system and run obliquely forward to the epithelium deep in the valleys of the ciliary processes. Anteriorly, the zonular plexus splits into the two branches of the "zonular fork," which run respectively to the anterior and posterior aspect of the lens. Thus the zonular plexus can act as a fulcrum. The three-dimensional architecture of the zonular apparatus is consistent with a new concept of accommodation.