Trachea mucous membrane. Coloured scanning electron micrograph (SEM) of a fractured mucous membrane of the trachea (wind pipe), showing the epithelium and underlying connective tissue. The upper epithelial surface is covered in a mixture of secretory cells (brown) and ciliated cells (pink). The tall columnar epithelium (green) is exposed with some nuclei visible, and the underlying connective tissue (lamina propria) is seen at bottom. Magnification: x1000 when printed at 10 centimetres wide.