The human penis is anatomically divided into two continuous areas—the body, or external portion, and the root. The root of the penis begins directly below the bulbourethral glands with a long cylindrical body of tissue known as the corpus spongiosum (or corpus cavernosum urethrae). This tissue extends through the body of the penis to the tip, where it expands into a mushroom-shaped structure called the glans penis. Running through the centre of the corpus spongiosum is the urethra, a common passage for semen and urine; the urethra ends in a slitlike opening at the tip of the glans penis.