Other visceral organs include a thin-walled, nearly transparent swim bladder, the kidney just dorsal to that and running the full length of the visceral cavity. The kidney covers the dorsal aorta on the ventral surface of the vertebral column and encloses the posterior vena cava. The urinary ducts can usually be seen on the ventral surface of the kidney. They meet somewhat anterior to the posterior end of the kidney and descend as a single duct around one side of the swim bladder. An expansion of this descending portion of the urinary duct serves as a urinary bladder. The bladder is connected to the urogenital papilla as are testes in mature males. The gonads develop dorso-laterally in the anterior visceral cavity in both sexes, but the ovaries have no ducts connecting the urogenital papilla, eggs are simply shed into the visceral cavity. The only major organ remaining unmentioned is the spleen. In salmonids this lays ventrally, just above the pelvic fins, attached to the posterior side of the major visceral mass.