422 



THE URINARY APPARATUS. 



border being concave and presenting a fissure the hilum at 

 which the vessels, the nerves, and the ureter enter the organ. 

 When the kidney is longitudinally cut in two, it is seen to be 

 made up of an external or cortical portion cortex and an in- 

 ternal or medullary portion medulla. The medullary portion is 

 made up of numerous pyramids (those of Malpighi), from 8 to 18 

 in number, and, dipping down between them, as well as forming 



the outer part of the kidney, is 

 the cortical portion. Each pyra- 

 mid terminates in a papilla pro- 

 jecting into a calyx, which, with 

 the calices of other pyramids, 

 forms the pelvis, the upper dilated 

 cavity of the ureter. 



Tubuli Uriniferi (Figs. 239, 

 240). At each papilla there open 

 about 20 uriniferous tubules, which 

 can be traced to the base of the 

 pyramid. Each tubule continues 

 into the cortical portion of the 

 kidney, where it is larger and 

 becomes convoluted, narrowing 

 again and entering the pyramid, 

 in which it again becomes straight, 

 forms a loop, and re-enters the 

 cortical portion, again becomes 

 convoluted, and finally terminates 

 in a spherical body, the Malpigh- 

 ian capsule or capsule of Bowman. 

 This complicated structure 

 may, perhaps, be traced more 

 easily in the opposite direction. 

 Beginning with the Malpighian 

 capsule in the cortical portion, 

 there is next the convoluted 

 tubule, which, as it passes into 

 the medullary portion, becomes 

 straight and is known as the 

 "descending limb of Henle's 

 loop." This bends on itself, 

 forming the ascending limb, like- 

 wise straight, passes back into 



the cortex, becomes convoluted, and enters a straight collecting 

 tube which opens at the apex of a pyramid. 



The uriniferous tubules are lined with epithelium, which varies 

 at different parts of their course. The epithelium which lines the 

 capsules and the neck, and which covers the glomerulus, is flattened, 



FIG. 239. Diagram of two urinif- 

 erous tubules: 1, Malpighian tuft 

 surrounded by Bowman's capsule; 

 2, constriction or neck ; 3, proximal 

 convoluted tubule ; 4, spiral tubule ; 



5, descending limb of Henle's loop; 



6, Henle's loop ; 7 and 8, ascending 

 limb of Henle's loop ; 9, wavy part of 

 ascending limb of Henle's loop; 10, 

 irregular tubule ; 11, distal convoluted 

 tubule ; 12, first part of collecting 

 tube ; 13 and 14, straight part of col- 

 lecting tube ; 15, excretory duct of 

 Bellini (Tyson and Brunton, after 

 Klein and Noble Smith). 



