THE URINIFEROUS TUBULES 339 



lobule. The larger interlobular arteries and veins lie at the 

 periphery, where they supply branches to several adjacent lobules. 



THE RENAL CONNECTIVE TISSUES. The kidney is envel- 

 oped by a fibrous capsule which is loosely attached to the substance 

 of the organ and contains the usual proportion of elastic fibres 

 together with a little smooth muscle. At the hilum of the organ 

 the capsule is continuous with the connective tissue which en- 

 velops the renal pelvis, infundibula, and calyces, and which, in the 

 intervals between adjacent calyces, comes into relation with the 

 cortical substance of the columns of Bertini. 



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 columns of Bertini, where they enter or 

 leave the renal tissue. Sympathetic nerve fibres 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 urinif- 

 erous tubules are loosely united. If the epithelium of these 

 tubules is removed, a delicate fibrous network remains ; this net- 

 work incloses a homogeneous basement membrane upon which the 

 lining epithelium ordinarily rests. Elastic fibres scarcely occur 

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

 increased in amount about the larger blood vessels, the Malpighian 

 bodies of the cortex, and the small blood vessels of the boundary 

 zone of the medulla. At the apex of the Malpighian pyramid it 

 invests the large ducts of Bellini in considerable quantity. 



THE URINIFEROUS TUBULES. The uriniferous tubules 

 begin in the cortical labyrinth as the capsules of the Malpighian 

 bodies. Assuming a tubular form they then pursue a tortuous 

 course through the labyrinth 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 medullary 

 ray and returns to the region of its origin, where it becomes again 

 convoluted. A short arched tubule connects this convoluted por- 

 tion with a straight collecting tubule of the medullary ray. The 

 collecting tubules traverse the whole length of the medullary ray 



