120 THE KIDNEYS. 



not very regular. In the middle it is. largely indented ; in this 

 indentation is a deep fissure, which separates the two broad sur- 

 faces or sides of the gland from each other ; and here the breadth 

 of the posterior surface is evidently greater than the anterior. 



Each of the kidneys receives a large artery, which proceeds 

 immediately from the aorta, nearly in a rectangular direction. 

 A vein, which opens into the vena cava, accompanies the 

 artery. It is obvious, from the situation of the kidneys with 

 respect to the great vessels, that the artery on the right side 

 must be longer than that on the left, and that the reverse of 

 this must be the case with the veins ; the veins are also anterior 

 to the arteries. At the great fissure these vessels divide into 

 several branches, which enter the kidney at that place. The 

 branches of the vein are before and above ; those of the artery 

 are below, and in the middle. Surrounded more or less by the 

 branches of those vessels, is a membranous sac ; the breadth of 

 which extends from above downwards. This sac terminates 

 in a tube that proceeds from the lower part of the fissure down 

 to the bladder. The sac is denominated the pelvis of the kid- 

 ney, and the tube a ureter: each of these parts will soon be 

 more particularly described. 



The substance of the kidney, as has been already said, is 

 uniform in its texture, and of a reddish brown color. When 

 it is divided by an incision made lengthways, and from its 

 convex to its concave edge, there appears to be a small differ- 

 ence in the different parts of it. The exterior part, which is 

 called cortical, is rather more pale in color and softer in 

 consistence than the internal part. It varies in thickness, so 

 that some writers have described it as equal to two lines, and 

 others to one-third of the kidney. In a majority of subjects it 

 will be found between the two statements. 



The interior part is called medullary, or tubular, and appears 

 to be composed of very fine tubes. These tubes are so 

 arranged, that a number of papillae or cones are formed by 

 their convergence, and project into the fissure of the kidney. 

 These papillae have been supposed to consist of a substance dif- 

 ferent from either of the two above mentioned, but they appear 

 to be formed merely by the tubular part. 



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