The development of the external genitalia of males begins between seven and nine weeks after conception, in response to the production of a hormone called dihydrotestosterone by the testes. Before this time, the external genitalia of the male and female are indistinguishable.

During development, a region called the genital tubercle elongates to form the penis. Urogenital folds move toward each other to form a groove that will become the urethra (which connects to the bladder and through which urine is expelled). The urethral connection to the outside world through the penis is established between 11 and 14 weeks after conception. By 11 weeks the scrotum has developed as well.

The penis is the most obvious feature of the male external genitalia. The other constituents are the pubic air and the scrotum. The penis consists of a body (also called the shaft) and glans (also called the head...