TOPOGRAPHY OF THE KIDNEY 337 



The Medulla of the kidney consists of a number of these coni- 

 cal Malpighian pyramids (usually twelve to fifteen) each of whose 

 apices, as already stated, is received into the extremity of a renal 

 calyx. The base of each Malpighian pyramid is embedded in the 

 adjacent renal cortex, and that portion of the cortex which is 

 interposed between the bases of adjacent pyramids, and thus 

 brought into relation with the fibrous and adipose tissue which 

 envelopes the pelvis and calyces at the hilum of the organ, com- 

 poses the cortical columns of Bertini. 



Each Malpighian pyramid may be subdivided into a central 

 free portion, the apical or papillary zone of the medulla, which 

 is received into a calyx, and an outer or basal portion, which is 

 embedded in the renal cortex and is known as the boundary zone of 

 the medulla. These two portions of the medulla, the papillary and 

 boundary zones, can be readily distinguished, since the latter con- 

 tains only narrow tubules and is highly vascular, while the former, 

 relatively deficient in blood vessels, contains the broad termina- 

 tions of the uriniferous tubules, the so-called ducts of Bellini, 

 which converge toward the apex of the Malpighian pyramid where 

 they open into the calyces. 



The Cortex of the kidney, on careful observation, presents 

 numerous dark lines or delicate columns which radiate from the 

 base of the Malpighian pyramids outward toward the surface of the 

 organ. These radiating columns are the medullary rays * (pyra- 

 mids of Ferrein). They contain straight portions of the urinife- 

 rous tubules, only these are continuous with the similar tubules in 

 the boundary zone of the medulla. 



That portion of the cortex which invests the medullary rays, 

 and which includes all the remaining cortical portions of the 

 organ, consists of extremely tortuous tubules, and is characterized 

 by the presence of small globular bodies, each of which contains a 

 tuft of capillary vessels. These are the Malpighian bodies (renal 

 corpuscles) which are characteristic of the kidney. The portion 

 of the cortex in which they occur includes the entire cortical sub- 

 stance with the exception of the medullary rays, and is known as 

 the TQ^^Jab^rinth. The labyrinth is subdivided into : 1, the 

 columns of Bertini, already mentioned ; 2, the intercolumnar 



* These columns lie within the cortex and not, as their name might be taken 

 to indicate, in the medulla. They are termed medullary rays because of their 

 peculiar relation to the medulla, from which they extend outward in a radial 

 direction. 



