528 THE KIDNEYS. 



perform some office connected with embryonic life. The anatomy of these 

 organs in the foetus will be found in the succeeding chapter. 



In structure they are composed of two substances, cortical and medul- 

 lary. The cortical substance is of a yellowish colour, and consists of 

 straight parallel columns placed perpendicularly side by side. The me- 

 dullary substance is generally of a dark brown colour, double the quantity 

 of the yellow substance, soft and spongy in texture, and contains within 

 its centre the trunk of a large vein, the vena supra-renalis. It is the large 

 size of this vein that gives to the fresh supra-renal capsule the appearance 

 of a central cavity : the dark-coloured pulpy or fluid contents of the cap- 

 sule, at a certain period after death, are produced by softening of the me- 

 dullary substance. Dr. Nagel* has shown, by his injections and micro- 

 scopic examinations, that the appearance of columns in the cortical substance 

 is caused by the direction of a plexus of capillary vessels. Of the numer- 

 ous minute arteries, supplying the supra-renal capsule, he says, the greater 

 number enter the cortical substance at every point of its surface, and, after 

 proceeding for scarcely half a line, divide into a plexus of straight capil- 

 lary vessels. Some few of the small arteries traverse the cortical layer, 

 and give off, in the medullary substance, several branches which proceed 

 in different directions, and re-enter the cortical layer to divide into a ca- 

 pillary plexus in a similar manner with the first described. From the 

 capillary plexus, composing the cortical layer, the blood is received by 

 numerous small veins which form a venous plexus in the medullary sub- 

 stance, and terminate at acute angles in the large central vein. 

 According to the more recent researches of Oesterlen and Mr. Simon, 

 the appearance of columns is due to groups of small corpuscles or cyto- 

 blasts associated with elementary granules and fat-cells collected together 

 in the form of parallel cylinders or cones, each group being enclosed in a 

 tube of delicate membrane (limitary membrane). The medullary sub- 

 stance and intercolumnar spaces contain cyto-blasts uniformly scattered 

 and interspersed with granules and fat-cells. Oesterlen found also, occa- 

 sionally, in the medullary substance elongated spaces, without lining 

 membrane, containing a thick greyish- white fluid. 



Vessels and Nerves. The supra-renal arteries are derived from the 

 aorta, from the renal, and from the phrenic arteries; they are remarkable 

 for the innumerable minute twigs into which they divide previously to 

 entering the capsule. The supra-renal vein collecting the blood from the 

 medullary venous plexus, and receiving several branches which pierce the 

 cortical layer, opens directly into the vena cava on the right side, and into 

 the renal vein on the left. 



The Lymphatics are large and very numerous ; they terminate in the 

 lumbar glands. The nerves are derived from the renal and from the 

 phrenic plexus. 



THE KIDNEYS. 



IV kidneys, the secreting organs of the urine, are situated in the lum- 

 bar regions, behind the peritoneum, and on each side of the vertebral 

 column, which latter they approach by thi-ir upper extremities. Each 

 kidney is between four and five inches in length, about two inches and a 

 half in breadth, somewhat more than one inch in thickness, and weighs 

 three and five ounces. The kidneys are usually enclosed in 9 



Muller's Archiv. 1830. 



