阴茎末端的一些皮肤形成游历悬挂的皱褶，就是大家熟知的包皮或阴茎包皮。这快包皮通常覆盖着被称为龟头的阴茎头。但是，在勃起的情况下，龟头从包皮突出而且完全暴露。

Foreskin
Toward the end of the penis some of this skin forms a freely hanging fold known as the foreskin or prepuce. This foreskin normally covers the tip or head of the penis called the glans. In the case of an erection, however, the glans protrudes from the foreskin and becomes fully exposed.