THE EXCRETORY SYSTEM 



The necessity for urea excretion is shown by the fact that 

 all animals, even microscopic ones, have organs for its 

 removal ; although these organs are known by different 

 names, in all cases they correspond in function to the 

 human kidneys. 



THE KIDNEYS 



The kidneys are located one on either side of the body, in 

 the "small" of the back, a little to each side of the backbone 

 and a trifle below the eleventh pair of ribs, the left kidney 

 lying somewhat higher up than 

 the right; Fig. 108. The peritoneal 

 lining of the body cavity, is 

 stretched tightly over them. 

 They are firm in texture and 

 dark red in color. Figure 108 

 shows each kidney to be oval in 

 general shape with a depression 

 on the side toward the backbone, 

 thus having a form known as 

 "kidney shape." From the de- 

 pression a tube, the ureter, leaves 

 the kidney and extends down- 

 ward to the bladder. Close by 

 the exit of the ureter the renal 

 artery enters the kidney and the 

 renal vein leaves it. 



The internal structure of a kidney appears somewhat as 

 in Figure 109. The ureter is large like a funnel as it leaves 

 the organ and is continuous with a space, called the pelvis, in 

 he body of the kidney itself. Protruding from the kidney 



bstance into the mouth of this funnel are conical structures 

 f soft tissue, eight to eighteen in number, called the Mai- 

 pyramids. On the apices of these are the openings 



FIG. 108. DIAGRAM 



Showing the position of the kidneys 

 and their connections. 



