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The foreskin (also known as the ''prepuce'') is the double-layered fold of smooth muscle tissue, blood vessels, neurons, [[skin]], and [[Preputial mucosa|mucous membrane]] part of the [[penis]] that covers and protects the [[glans penis]] and the urinary meatus.<ref name="cold-taylor1999"/> There are four layers in the foreskin. The top layer is either epidermis or mucosa, depending on location. The second layer is the lamina propria. The third layer is the [[dartos]]. The fourth layer is the dermis. The adult foreskin measures about 3 inches by 5 inches or [[The Foreskin: 15 Square Inches of Erogenous Tissue| 15 square inches]].<ref name="taylor1996">{{TaylorJR LockwoodAP TaylorAJ 1996}}</ref> The two foreskin layers provide a [[skin]] reserve. When the penis becomes erect, the foreskin may wholly or partially unfold to provide the necessary [[skin]] to allow for expansion of the penis during [[erection]].