THE KIDNEY 427 



the organ the capsule is continuous with the connective tissue which 

 envelops the renal pelvis, inf'undiliula. and calyces, and which, in the 

 interval.- hetwren adjacent calyces, comes into relation with the cortical 

 substances of the renal columns. 



This connective tissue of the hilum is of the areolar variety and 

 contains much adipose tissue. It supports the large arteries and veins 

 as they pass along the surface of the renal pelvis on their way to and 

 from the renal columns, where they enter or leave the parenchyma. 

 Sympathetic nerve fibers and a few small ganglia are also found in this 

 region. 



The connective tissue of the interior of the organ, interstitial tissue, 

 is very scanty, and in most parts consists only of isolated fibrils which 

 invest the blood-vessels and the renal tubules. It forms a very delicate 

 reticulum by which the walls of the uriniferous tubules are loosely united. 

 If the epithelium of these tubules is removed, a delicate fibrous network 

 remains ; this network incloses a homogeneous basement membrane upon 

 which the lining epithelium ordinarily rests. Elastic fibers scarcely 

 occur among the tubules of the kidney. The interstitial tissue is slightly 

 increased in amount about the larger blood-vessels, the renal corpuscles 

 of the cortex, and the small blood-vessels of the boundary zone of the 

 medulla. At the apex of the renal pyramid it invests the large papillary 

 ducts in considerable quantity. 



THE URINIFEROUS OR RENAL TUBULES 



The uriniferous tubules begin in the cortical labyrinth as the capsules 

 of the renal corpuscles. Assuming a tubular form they then pursue a 

 tortuous course through the pars convoluta and finally enter the boundary 

 zone of the medulla, where, much reduced in size, they form the loop of 

 Henle, which consists of a short, descending, thin limb, a U-shaped loop, 

 and a long, ascending or thick limb. This last division, after recrossing 

 the boundary zone of the medulla, enters a pars radiata and returns 

 to the region of its origin, where it becomes again convoluted. A short 

 arched tubule connects this convoluted portion with a straight collecting 

 hilnilc of the cortical ray. The collecting tubules traverse the whole 

 length of the ray, uniting with their fellows and receiving other arched 

 tubules along their entire course. They then cross the boundary zone 

 of the medulla, and finally, in the papillary zone, having meanwhile 

 received numerous accessions of straight collecting tubules, form the 



