Two electron micrographs of smooth muscle cells in a small artery, surrounded by a light gray zone of interspaces composed of an elastic fiber and collagen-rich basement membrane. The elastica interna is a lamina composed of elastin fibers, and enables arteries to stretch. Figures 27 (upper) and 28 (lower) from Chapter 1 (The Cell Surface) 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.