CHAPTER XVIII. 



THE KIDNEYS AND THE SKIN. 



General Arrangement of the Nitrogen-excreting Or- 

 gans. These organs are (1) the kidneys, the glands which 

 secrete the urine; (2) the ureters or ducts of the kidneys, 

 which carry the secretion to (3) the urinary bladder, a 

 reservoir in which it accumulates and from which it is ex- 

 pelled from time to time through (4) an exit tube, the 

 urethra. The general arrangement of these parts, as seen 

 from behind, is shown in Fig. 73. The kidneys, R, lie 

 at the back of the abdominal cavity, opposite the upper 

 lumbar vertebrae, one on each side of the middle line. 

 Each is a solid mass, with a convex 'outer and a concave 

 inner border, and its upper end a little larger than the 

 lower. From the abdominal aorta, A, a renal artery, Ar, 

 enters the inner border of each kidney, to break up within 

 it into finer branches, ultimately ending in capillaries. 

 The blood is collected from these into the renal veins, Vr, 

 one of which leaves each kidney and opens into the inferior 

 vena cava, Vc, which carries it, after having lost water and 

 urea in the kidney, back to the heart. From the concave 



Name the chief organs concerned in removing from the body its 

 nitrogenous waste matters. Describe the general arrangement of 

 these organs. Describe the form of a kidney. What vessel supplies 

 it with blood? What vessel carries blood out of the kidney? What 

 has the blood carried off from a kidney lost while flowing through 

 that organ? 



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