1. The subfornical organ of the cat contains various types of morphologically different synapses. The most frequent type is that of Gray 1. In addition, Gray 2 type junctions are seen. Large, multifocal synapses occur at perikarya and large dendritic stems. The most conspicuous synapse is designated “crest synapse with subjunctional bodies”; it occurs both in axodendritic and axosomatic junctions. No spine synapses have been observed. 2. All presynaptic endings are characterized by a polymorphic vesicular material. Clear vesicles range from 200–800 A in diameter and may be spheric, elliptoid or flat. A small number of dark-cored vesicles (1,000–1,500 A) is also present in most terminals; they are often located more distally from the synapse. 3. Crest synapses differ from spine synapses with respect to the profile; they typically contain two junctions, one on either side of the crest within a distance of 1,500 A in a back-to-back position. In between, there is a lattice of postsynaptic spherules in a hexagonal or triagonal array. The spherules seem to be interconnected by a network of fine extensions which may be attached to the dense material apposed to the postsynaptic membrane. 4. The subsynaptic bodies seem to occur exclusively in crest synapses with double contacts and their as yet mysterious function may be understood in terms of either mechanical buttresses or in context with the “double plug” function of a postsynaptic crest. The hypothesis that they may represent a specific innervation is rejected since identical pre- and postsynaptic elements were found to form both crest synapses with subjunctional bodies and classical, non-profiled junctions.