either of two pea-shaped glands in the male, located beneath the prostate gland at the beginning of the internal portion of the penis; they add fluids to semen during the process of ejaculation (q.v.). The glands, which measure only about 1 cm (0.4 inch) in diameter, have ducts that empty into the urethra, the tube through which both urine and semen pass. They are composed of a network of small tubes, or tubules, and saclike structures; between the tubules are fibres of muscle and elastic tissue that give the glands structural support. Cells within the tubules and sacs contain droplets of mucus, a thick protein compound. The fluid excreted by these glands is clear and thick and acts as a lubricant; it is also thought to function as a flushing agent that washes out the urethra before the semen is ejaculated; it may also help to make the semen less watery and to provide a suitable living environment for the sperm. See also prostate gland; seminal vesicle.