A mucocutaneous junction, or mucocutaneous boundary, is a region of the body in which mucosa transitions to skin. Mucocutaneous zones occur in animals, at the body orifices. In humans, mucocutaneous junctions are found at the lips, nostrils, conjunctivae, urethra, vagina (in females), foreskin (in males), clitoral hood (in females), and anus. In the nostrils the mucocutaneous junction has a dense microvascular network, and shows a marked similarity to that found in the mouth, between the oral mucosa and the lips. At a mucocutaneous junction, epithelium transitions to epidermis, lamina propria transitions to dermis, and smooth muscle transitions to skeletal muscle...