The corpus cavernosum are two areas of erectile tissue which run along the length of the penis, and fill with blood during erection. They are separated by a membrane of connective tissue along the length of the shaft, and hold about 90% of the blood in the penis during erection. The remainder fills a similar area of erectile tissue, called the corpus spongiosum, which surrounds the urethra.
It is an urban myth that piercing the corpus cavernosum will make you bleed to death, although more bleeding can be expected than with other male genital piercings. Although placement can vary, Ampallang piercings often pass through this area.