STKUCTUKE OF THE KIDNEYS. 



769 



a rib's breadth lower than the left. The kidneys are placed behind the 

 peritoneum, and are held in position by their bloodvessels, nerves, and 

 the excretory ducts, called the ureters ; they are likewise surrounded 

 by an areolar tissue, usually loaded with fat, forming the so-called 

 adipose coat, which, being a bad conductor of heat, serves to preserve 

 the temperature of these organs. The shape of the kidney is well 

 known and characteristic. Each is about 4 inches long, 2 wide, and 1 

 thick ; the left one is rather longer and thinner than the right. In 

 the male, each weighs from 4J to 5J ounces ; in the female, about J oz. 

 less. The left kidney is generally about Joz. heavier than the right. 

 The weight of the two glands together, in proportion to that of the 

 body, is about as 1 to 240. The specific gravity of the kidney sub- 

 stance is 1050. Its chemical composition is 76 percent, of water, 15 

 of albuminoid substance, only 1 of fatty or resinous matter, which is 

 chiefly cholesterin, together with certain extractives, including inosite, 

 cystin, taurin, and xanthin. 



If one kidney be atrophied or destroyed by disease, the other one 

 usually enlarges. In certain cases, the kidneys are joined by a trans- 

 verse portion of gland substance, the upper border of which is gener- 

 ally concave, the resulting mass forming the so-called horseshoe kid- 

 ney. The two conjoined kidneys are sometimes found on one or other 

 side of the lumbar region, or even in the pelvic cavity. A few in- 

 stances are on record of the presence of three kidneys, the third 

 gland, usually called a movable or floating kidney, being placed either 

 on one side of the vertebral column, or in front of it, or else in the 

 pelvis. 



The upper end of each kidney is surmounted by the corresponding 

 suprarenal body. Its internal concave border presents towards its 

 middle a deep longitudinal fissure, called the hilus, which leads into a 

 cavity within the organ, named the sinus. 

 This gives exit and entrance to the blood- 

 vessels, absorbents, and nerves, and also to 

 the ureter ; the renal or emulgent veins 

 here lie in front, the ureter behind, and the 

 renal arteries between them. 



The kidney is everywhere closely invest- 

 ed by a proper firm, smooth, fibrous coat, 

 which may be readily torn off ; it is, how- 

 ever, connected with the gland substance 

 by numerous fine fibrous processes and ves- 

 sels ; it passes in at the hilus, lines the 

 cavity of the sinus, and is even reflected 

 on to the ureter and bloodvessels. 



On making a longitudinal section of the 

 kidney through the hilus, the solid gland 

 substance is found to consist of an outer 

 cortical portion, and of a deep-seated med- 

 ullary portion. The cortical substance is 

 continuous over the whole organ, and dips 

 in between the different parts of the medul- 



49 



109. 



Fig. 109. Diagram of a longitudinal 

 section of the kidney. 1. Cortical sub- 

 stance. 2. A pyramid. 2'. Mammilla 

 or papilla of a pyramid, lying in its 

 opened calyx. 3. A portion of ureter 

 expanding above into the pelvis of the 

 kidney, then dividing into the infun- 

 dibula, and afterwards into the calyces. 



