THE VERTEBRATE BODY 



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the duct which in the human body is a true ureter in both sexes. The 

 kidneys lie behind the body cavity ; that is, they are between the peri- 

 toneum and the muscle wall of the back. This makes it possible to 

 operate on the kidney to remove stones from the pelvis by going through 

 the back without actually entering the body cavity. This keeps air out 



Dorsal aorta 

 Vena cava 



Renal artery 

 Renal vein 

 Kidney 



Ureter 



Urinary bladder 



Urethra 



Fig. 24.2. Diagram showing the position of the excretory organs in the human body. 



of the cavity and greatly reduces the danger of peritonitis, an infection 

 of the membranes covering the organs. 



The ureters empty directly into the urinary bladder which is capable 

 of great distention. The bladder in the female empties directly to the 

 outside by means of an elongated neck, the urethra. In a man the ex- 

 cretory system gets mixed up with the reproductive system again, but 

 not as intimately as in the frog. The sperm ducts join the urethra just 



