358 



A YEAR IN SCIENCE 



Vein 



and the .exact location of them. From each of the 

 kidneys a tube, the ureter, passes to the bladder. The 



latter is a muscular 

 sac situated in the 

 lower part of the ab- 

 dominal cavity. From 

 y it a tube, the urethra, 

 carries the urine to 

 the external urinary 

 opening. 



Each kidney is com- 

 posed of an enormous 

 number of compli- 

 cated tubes. Around 

 these tubes are many 

 blood capillaries. 

 From the blood, while 

 it is in the kidneys, 

 there is removed, by 

 means of secreting 

 cells in the tubes, 

 large quantities of water holding in solution urea 

 and the other excretions from the kidneys. This 

 waste material is called urine. From these tubes 

 the urine passes into a cavity in the kidney from which 

 it is poured through the ureter to the bladder. When 

 a sufficient amount has collected in the bladder, the 

 muscular walls contract and it is expelled. It will thus 

 be seen that the kidneys do not make the waste 



Bladde 



UrethYa 



Fig. 167. The kidneys and their 

 connections. 



