An erection is the stiffening expansion and orthogonal reorientation of the penis, which occurs during sexual arousal. The skin around the penis and the urethra share the same embryonic origin as the labia minora in females. Most of the penis develops from the same embryonic tissue as the clitoris in females. It is a passage both for urination and ejaculation of semen ( see male reproductive system.) The urethra traverses the corpus spongiosum, and its opening, the meatus ( / m iː ˈ eɪ t ə s/), lies on the tip of the glans penis. The human male urethra passes through the prostate gland, where it is joined by the ejaculatory duct, and then through the penis. The body of the penis is made up of three columns of tissue: two corpora cavernosa on the dorsal side and corpus spongiosum between them on the ventral side. The main parts are the root (radix) the body (corpus) and the epithelium of the penis including the shaft skin and the foreskin (prepuce) covering the glans penis. The human penis is an external male intromittent organ that additionally serves as the urinal duct.
