THE KIDNEYS

                     

THE Kidneys, two in number, are situated in the back part of the abdomen, and 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. Theil' 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. 'I'he left is somewhat longer, though narrower, than the right. The weight of the kidney in the adult male varies from 4t ounces to 6 ounces; in the adult female, from 4 ounces to 5t ounces. The com­bined 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 con­tact with the posterior part of the under surface of the right lobe of the liver. on which it produces a concave impression, the impreesio renalis (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. 'I'he relation of the second part of the duodenum to the front of thc 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 some­times with the third part of the duodenum. Near its outer border the anterior sur­face lies behind the spleen and the splenic flexure of the colon.