Fig. 7. A. A freeze-fracture view of the photoreceptor synaptic ridge characterized by a densely packed array of P-face particles (ridge). Adjacent to the ridge are three vesicle fusion sites (arrows). (× 100,000) B. A horizontal cell dendrite (h) showing a dense array of P-face particles (arrow), which may represent glutamate receptors (× 115,000). (Data of A.R. Nagy and P. Witkovsky)