XIV 



\v\si i: \M i x< k \ 



161 



'" 



of tlie abdomen, is a bag, tlie walls of which arc mi| 

 of plain nnis< ular tissue, lined internally by a layer of mucous 

 membrane. It occupies very little space when it is empty, 

 but can be distended to a large size. When moderately 

 distended it will hold a pint. 



The function of the kidneys is to secrete urine. The 

 function of the ureters is to conduct the urine from the 

 kidneys to the bladder. 

 The function of the bladder 

 is to store the urine and to 

 discharge it at intervals. 

 The ureters pass obliquely 

 through the wall of the 

 bladder to open into its 

 interior, and this assures 

 a valve-like closure of the 

 openings, so that urine can 

 always trickle into the 

 bladder, but cannot be 

 forced back again from the 



bladder into the ureters. 

 The tube leading out of the 

 bladder is the urethra. 

 Around the opening from 

 the bladder into the urethra 

 are a number of plain 



muscular fibres cin ularly FIG. 73.- Section of the kidney, 



placed, forming what is ( -f, cortex; .I/, medulla; I'y, pyramids; /', 

 called a Sphincter mUBCle. pelvis; U, ureter; KA, renal artery. 



These muscular librcs are 



kept contracted, and so the opening is kept closed. The 

 bladder, when a quantity of urine has accumulated in it, can be 

 emptied at will, the sphincter muscle is relaxed, and the con- 

 traction of the muscular fibres of the bladder drives the urine 

 out along the urethra. 



Structure of the Kidney.- Obtain a kidney of a simp. 



Notice its concavo-convex shape. '1 here is often some fat 

 on the surface, especially at the hilus. Carefully remove the 

 fat little by little from round the hilus, and look for the whitish 

 ureter and the reddish (from remains of blood) artery and 



y 



