There are three separate chambers in a normal penis: two of which are erectile, interconnected and occupy the penis volume, called corpus cavernosum, and the urethra, a tube that conducts both urine and semen. The erectile chambers are connected to the pubic bone and go from the abdominal part to the visible part of the penis.

This anchor helps keeping a rigid penis when the chambers are filled with blood. Each erectile chamber is built by a sponge-like tissue that fills up with blood during excitement. The blood is kept in the penis, increasing its size and hardening it for penetration.