Illustration of a cross-section through the male urogenital tract. Prominently seen, at above centre, is the bladder (red). It receives urine from the kidneys through two ureters, one of which is seen (top right, brown). Urine then passes down the urethra which, at lower left, is surrounded by spongy erectile tissue of the penis. The male urethra also receives sperm and seminal fluids during ejaculation. Sperm is produced in testes; a scrotal sac which holds the testis is at bottom left (yellow). While seminal fluids are produced by a prostate gland (centre, below the bladder); by seminal vesicles (spiral shaped, centre right); and Cowper's gland (yellow, lower centre).