2O6 



NORMAL HISTOLOGY. 



Cortex 



Interlobar 

 blood-vessel 



striated renal pyramid, is the cortex. The medulla includes the conical 

 areas of the pyramids and partially occupies the inner two thirds of the 

 thickness of the organ. The cortex constitutes the bulk of the kidney, 

 forming the entire surface, including the lips of the hilum, and receiving 

 and surrounding the bases of the pyramids. The cortical tissue, further, 

 penetrates between the pyramids, separating them and in places gaining the 

 sinus. These interpyramidal extensions are the renal columns, or columns 

 of Berlin, and consist of typical cortical substance. Since the branches of the 

 renal blood-vessels lie within the interlobar connective tissue separating 

 the primary subdivisions of the foetal organ, these vessels never enter the 

 kidney-substance by passing into the papillce, but always at the side of and 



between these. They sink 

 into the renal substance, 

 therefore, through the areas 

 occupied by the renal col- 

 umns, the free surfaces of 

 which are pitted by the 

 vascular foramina. 



On inspection with a 

 hand-glass, it will be seen 

 that the cortex is not uni- 

 form, but subdivided into 

 radially disposed darker 

 and lighter tracts. The lat- 

 ter, longitudinally striated 

 and wedge-shaped, are the 

 medullary rays, or pars 

 radiata, since they are ap- 

 parently continuations of 

 the medullary tissue. The 

 darker tracts, between the 

 medullary rays, constitute 

 the labyrinth, or pars con- 

 voluta, and appear granular 

 owing to the tortuous course 

 of the component urinife- 

 rous tubules. The labyrinth 

 is studded with bright red points marking the position of minute vascular 

 tufts or glomeruli; these are limited to the labyrinth and, therefore, never 

 present within the medullary rays or the renal pyramids, although found 

 within the columns of Berlin. 



On sectioning minutely injected organs, it will be observed that the 

 larger interlobar arteries, on gaining the boundary zone between the 

 cortex and the medulla, break up into smaller branches, some of which pass 

 towards the surface, while others change their direction and assume a more 

 horizontal course. The terminal twigs "end-arteries," since anastomoses 

 are wanting run generally perpendicular to the exterior of the kidney and 

 occupy the centres of the tracts separating the medullary rays. The latter 

 are, therefore, the axes of minute conical masses of renal substance, the 

 cortical lobules, whose bases lie at the surface of the kidney and the apices 

 within the pyramids of the medulla. From the foregoing it is evident that 

 each renal pyramid receives a group of cortical lobules, the component 

 tubules of which, on entering the pyramid, become progressively less 



Renal papilla 

 Renal pelvis 



Part of sinus 



Renal papilla, 

 apex of 

 pyramid 



FIG. 254. Longitudinal section of kidney, showing divisions of 

 renal substance and relations of pelvis and calyces. 



