The penis is an external organ of the male reproductive system. It consists of three parts: 1) the root where the penis attaches to the wall of the abdomen; 2) the shaft or body; and 3) the glans, which is the tip of the penis. The body of the penis has a tubular, cylindrical shape and surrounds the urethra. Spongy tissue that can expand and contract fills the body or the penis. There is a slit opening at the tip of the glans through which urine is excreted and semen is ejaculated through the urethra.