CHAPTER XXVII. 



THE KIDNEYS AND SKIN. 



General Arrangement of the Urinary Organs. These 

 consist of (1) the kidneys, the glands which secrete the 

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

 their secretion to (3) the urinary Uadder, a reservoir in 

 which it accumulates and from which it is expelled from 

 time to time through (4) an exit tube, the urethra. The 

 general arrangement of these parts, as seen from behind, is 

 shown in the figure opposite. The kidneys, R, lie in the 

 dorsal part of the lumbar region of the abdominal cavity, 

 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. From the concave border of each kidney proceeds 

 also the ureter, U, a slender tube from 28 to 34 cm. (11 to 

 13.5 inches) long, opening below into the bladder, Vu, on 

 its dorsal aspect, and near its lower end. From the 

 bladder proceeds the urethra, at Ua. The channel of each 

 ureter passes very obliquely through the wall of the 

 bladder to open into it; accordingly if the pressure inside 

 the latter organ rises above that of the liquid in the ureter, 

 the walls of the oblique passage are pressed together and 



