2O2 



THE VITAL PROCESSES 



cavity, one on each side of the spinal column. They 

 weigh from four to six ounces each, and lie between the 



abdominal wall and the peri- 

 toneum. Two large arteries from 

 the aorta, called the renal arteries, 

 supply them with blood, and they 

 are connected with the inferior 

 vena cava by the renal veins. 

 They remove from the blood an 

 exceedingly complex liquid, called 

 the urine, the principal constituents 

 of which are water, salts of dif- 

 ferent kinds, coloring matter, and 

 urea. The kidneys pass their 

 secretion by two slender tubes, the 

 ureters, to a reservoir called the 

 bladder (Fig. 87). 



Structure of the Kidneys. 

 FIG. 87. Relations of the Each kidney is a compound tubu- 

 kidneys. (Back view.) i. kr land and ig compose d chiefly 

 The kidneys. 2. Ureters. 3. . . . J 



Bladder. 4 . Aorta. 5. In- of the parts concerned in secretion. 



The ureter serves as a duct for 

 removing the secretion, while the 

 blood supplies the materials from 



which the secretion is formed. On making a longitudinal 

 section of the kidney, the upper end of the ureter is 

 found to expand into a basin-like enlargement which is 

 embedded in the concave side of the kidney. The cavity 

 within this enlargement is called the pelvis of the kidney, 

 and into it project a number of cone-shaped elevations 

 from the kidney substance, called the pyramids (Fig. 88). 



From the summits of the pyramids extend great num- 

 bers of very small tubes which, by branching, penetrate to 



ferior vena cava. 6. Renal 

 arteries. 7. Renal veins. 



