(b) Higher magnification shows the relationship of the many rounded, thin-walled alveoli (A) to alveolar ducts (AD). Alveolar ducts end in two or more clusters of alveoli called alveolar sacs (AS). Smooth muscle around the alveolar openings appears as eosinophilic "knobs" between adjacent alveoli. The alveoli here that do not show openings to the ducts or the sacs have their connections in planes of adjacent sections. X140. H&E. Source: Chapter 17. The Respiratory System, Junqueira’s Basic Histology, 13e Citation: Mescher AL. Junqueira’s Basic Histology, 13e; 2013 Available at: http://accessmedicine.mhmedical.com/DownloadImage.aspx?image=/data/books/mesc13/mesc13_c017f012.png&sec=42526958&BookID=574&ChapterSecID=42524603&imagename= Accessed: December 30, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved