1. AnatomyThe urethra (pl.: urethras or urethrae) is the tube that transports semen through the penis during ejaculation and urine from the urinary bladder to the external urethral orifice of the penis or vulva in placental mammals. The external urethral sphincter is a striated muscle that allows voluntary control over urination. The internal sphincter, formed by the involuntary smooth muscles lining the bladder neck and urethra, is innervated by the sympathetic division of the autonomic nervous system and is found both in males and females. == Structure == The urethra is a fibrous and muscular tube which connects the urinary bladder to the external urethral meatus. Its length differs between the sexes, because it passes through the penis in males. === Male === In the human male, the urethra is on average 18 to 20 centimeters (7 to 8 inches) long and opens at the end of the external urethral meatus. The urethra is divided into four parts in men, named after the location: There is inadequate data... from wikipedia.org