The Urinary Organs. 



THE KIDNEYS. 



THE Kidneys are two glandular organs, intended for the secretion of the -urine. 

 They are situated at the back part of the abdominal cavity, behind the peri- 

 toneum, one in each lumbar region, extending from the eleventh rib to near the 

 crest of the ilium ; the right one being lower than the left, from its vicinity to 

 the liver. They are usually surrounded by a considerable quantity of fat, and 

 are retained in their position by the vessels which pass to and from them. 



Relations. The anterior surface of the kidney is convex, partially covered by 

 the peritoneum, and is in relation, on the right side, with the back part of the 

 right lobe of the liver, the descending portion of the duodenum, and ascending 

 colon ; and on the left side with the great end of the stomach, the lower end of the 

 spleen, the tail of the pancreas, and the descending colon. 



The posterior surface is flattened, and rests upon the corresponding crus of the 

 Diaphragm, in front of the eleventh and twelfth ribs, on the anterior lamella of 

 the aponeurosis of the Transversalis which separates it from the Quadratus lum- 

 borum, and on the Psoas magnus. 



The superior extremity, directed inwards, is thick and rounded, and embraced 

 by the supra-renal capsule. It corresponds, on the left side, to the upper border 

 of the eleventh rib, and on the right side to the lower border. 



The inferior extremity, small and flattened, extends nearly as low as the crest 

 of the ilium. 



The external border is convex, and directed outwards towards the parietes of 

 the abdomen. 



The internal border is concave, and presents a deep notch, the hilus of the kidney, 

 more marked behind than in front. At the hilus, the vessels, excretory duct, 

 and nerves pass into or from the organ ; the branches of the renal vein lying in 

 front, the artery and its branches next, the excretory duct or ureter being behind 

 and below. On the vessels the nerves and lymphatics ramify, and much cellular 

 tissue and fat surrounds the whole. The hilus leads into a hollow space, the 

 sinus, which occupies the interior of the gland. 



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

 one inch in thickness ; the left one being somewhat longer and thinner than the 

 right. The weight of the kidney in the adult male varies from 4| oz. to 6 oz. ; 

 in the female, from 4 oz. to 5| oz., the difference between the two being about 

 half an ounce. The left is nearly always heavier than the right, by about two 

 drachms. Their weight in proportion to the body is about 1 to 240. The renal 

 substance is dense, firm, extremely fragile, and of a deep red color. 



The kidney is invested by a fibrous capsule, formed of dense fibro-areolar 

 tissue. It is thin, smooth, and easily removed from its surface, to which it is con- 

 nected by fine fibrous processes and vessels ; and at the hilus is continued inwards, 

 lining the sides of the sinus, and at the bottom of that cavity forms sheaths around 

 the bloodvessels and the subdivisions of the excretory duct. 



On making a vertical section through the organ, from its convex to its concave 

 border, it appears to consist of two different substances, viz., an external or cor- 

 tical, and an internal or medullary, substance. 



The cortical substance forms about three-fourths of the gland. It occupies the 

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