Upper: a gap junction on the boundary between two hepatic cells shows a typical narrow and straight interface. Lower: in some preparations, gap junctions appear curved, and project into one of the cells, possibly an artifact of tissue preparation. Images by Richard Wood appear as Figures 102 (upper) and 130 (lower) from Chapter 3 (Junctional Specializations) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB's BioEDUCATE website.