NO also plays a role in erection of the penis and clitoris. An erection is the stiffening and rising of the penis, which occurs during sexual arousal. The male genitalia are the penis and the scrotum. The testicles are placed in the scrotum behind the penis. The bulbocavernosus reflex is triggered by stimulation of the glans penis or clitoris. Phimosis is the inability to retract the foreskin over the glans penis. Neither age nor size of the flaccid penis accurately predicted erectile length. Circumcision is the removal of the foreskin from the human penis. Such damage can result in erectile dysfunction or disfigurement of the penis. "Fellatio" is oral sex performed on a penis. I unwrapped the paper holding them and gazed at his penis and scrotum. Human papillomaviruses are an established cause of cancers of cervix, skin, anus, and penis. Male primates have a pendulous penis and scrotal testes. Male felids urinate backwards by curving the tip of the glans penis backward. Scientific studies have been performed on the erect length of the adult penis.