THE URINARY ORGANS. 



THE KIDNEYS. 



fTlHE Kidneys, two in number, are situated in the back part of the abdomen, and 

 _L are for the purpose of separating from the blood certain materials which, 

 when dissolved in a quantity of water, also separated from the blood by the kid- 

 neys, constitute the urine. 



They are placed in the loins, one on each side of the vertebral column, behind 

 the peritoneum, and surrounded by a mass of fat and loose areolar tissue. Their 

 upper extremity is on a level with the upper border of the twelfth dorsal vertebra, 

 their lower extremity on a level with the third lumbar. The right kidney is 

 usually on a slightly lower level than the left, probably on account of the vicinity 

 of the liver. 



Each kidney is about four inches in length, two to two and a half in breadth, 

 and rather more than one inch in thickness. The left is somewhat longer, thougli 

 narrower, than the right. The weight of the kidney in the adult male varies from 

 4| ounces to 6 ounces ; in the adult female, from 4 ounces to 5^ ounces. The com- 

 bined weight of the two kidneys in proportion to the body is about 1 in 240. 



The kidney has a characteristic form. It is flattened on its sides and presents 

 at one part of its circumference a hollow. It is larger at its upper than its lower 

 extremity. It presents for examination two surfaces, two borders, and an upper 

 and lower extremity. 



Its anterior surface is convex, looks forward and outward, and is partially 

 covered by peritoneum. The right kidney in its upper three-fourths is in con- 

 tact with the posterior part of the under surface of the right lobe of the liver, on 

 which it produces a concave impression, the impressio renatis (page 918). 

 Toward its inner border it is covered by the second part of the duodenum, while 

 its lower and outer part is in relation with the hepatic flexure of the colon. The 

 relation of the second part of the duodenum to the front of the right kidney is a 

 varying one. The left kidney is covered above by the posterior surface of the 

 stomach, below the stomach by the pancreas, behind which are the splenic vessels. 

 Its lower half is in contact with some of the coils of the small intestine and some- 

 times with the third part of the duodenum. Near its outer border the anterior sur- 

 face lies behind the spleen and the splenic flexure of the colon. 



The kidneys are partly covered in front by peritoneum and partly uncovered. 

 On the right kidney, the hepatic area, that is to say that portion of the kidney 

 which produces the renal impression on the liver, is covered by peritoneum, which 

 therefore separates the kidney from the liver : the duodenal and colic areas are not 

 peritoneal, and these structures are connected to the kidney by loose connective 

 tissue ; at the lower and inner extremity is a small area, the mesocolic area, which 

 is covered by a layer of peritoneum of the greater sac and by the colic vessels. 

 On the left kidney, the gastric area is covered by the peritoneum of the lesser sac ; 

 the pancreatic and colic areas are non-peritoneal : Avhile, as on the right side, at the 

 lower and inner extremity, is an area, mesocolic, which is covered by the perito- 

 neum of the greater sac and by the colic vessels. 



The posterior surface of the kidney is flatter than the anterior and is directed 

 backward and inward. It is entirely devoid of peritoneal covering, being im- 

 bedded in. areolar and fatty tissue. It lies upon the Diaphragm, the anterior layer 

 of the lumbar aponeurosis, the external and internal arcuate ligaments, the Psoas 



985 



