The outer segments of the foveal cones of the rhesus monkey are about 40 microns long and 0.9 microns wide. They consist of stacks of membrane-limited, transverse discs about 140 A thick, surrounded by a plasma membrane. The inner segments are about 30 microns long and 2.5 to 3 microns wide at the base, and they taper gradually to a tip diameter of about 1.5 microns. They contain many long mitochondria which are oriented length-wise and are concentrated in the distal portion of the segment. The terminal pedicles show many synaptic contacts, probably as many as 36 per pedicle.