424 



THE URINARY SYSTEM 



funnel-form beginning of the ureter, toward the renal parenchyma 

 divides into two, sometimes three, infundibula, which in turn subdivide 

 into several calyces, each of which incloses the conical apex of a projecting 

 medullary or mini (Mdlpighian) pyramid. 



The Medulla. The medulla of the kidney consists of a number of 

 these conical renal pyramids (usually twelve to fifteen) each of whose 



apices, as already stated, is received 

 into the extremity of a renal calyx. 

 Occasionally a calyx may receive two 

 papillae. The base of each pyramid 

 is embedded in the adjacent renal 

 cortex, and that portion of the cor- 

 tex which is interposed between the 

 bases of adjacent pyramids, and thus 

 brought into relation with the fi- 

 brous and adipose tissue which en- 

 velops the pelvis and calyces at the 

 hilum of the organ, composes the 

 cortical renal columns (of Bertini). 

 Each renal pyramid may be sub- 

 divided 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 cor- 

 tex and is known as the boundary 



FIG. 397. LONGITUDINAL SECTION OF 

 KIDNEY. 



1, cortex; 1', cortical rays; 1", laby- 

 rinth; 2, medulla; 2', papillary portion 

 of medulla; 2", boundary layer of me- 

 dulla; 3, transverse section of tubules 

 in the boundary layer; 4, fat of renal 

 sinus; 5, artery; *, renal column of 

 transverse medullary rays; A, branch 

 of renal artery; C, renal calyx; U, ureter. 

 (After Tyson and Henle, from Hill.) 



zone of the medulla. These two por- 

 tions 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 terminations of 



the uriniferous tubules, the i><ii>illary duel* (of Bellini) which converge 

 toward the apex of the pyramid where they open into the calyces. 



The Cortex. The cortex of the kidney, on careful observation, pre- 

 sents numerous dark lines or delicate columns which radiate from the 

 base of the pyramids outward toward the surface of the organ. These 

 radiating columns are the medullary rays (pyramids of Ferrein] or 



