Smooth muscle bundles (HA15 S) are found in the lamina propria as bronchi transition to bronchioles between the elastic fibers and the seromucous glands (G). At lower magnification, the epithelium, smooth muscle, and seromucous glands can all be identified (HA15). The epithelium and the underlying CT down to the smooth muscle layer is called the mucosa. The seromucous glands secrete via ducts onto the surface of the epithelium.