THE KIDNEYS AND SKIN. 429 



and presses on its contents; the ureters being closed in the 

 way above indicated, the elastic fibres closing the urethral 

 exit are overcome, and the urethral muscles simultaneously 

 relaxing, the liquid is forced out. 



Naked Eye Structure of the Kidneys. These organs 

 have externally a red-brown color, which can be seen through 

 the transparent capsule of peritoneum which envelops them. 

 When a section is carried through a kidney from its outer to 

 its inner border (Fig. 133) it is seen that a deep fissure, the 

 hilus, leads into the latter. In the hilus the ureter widens 

 out to form the pelvis, D, which breaks up again into a 

 number of smaller divisions, the cups or calices. The cut 

 surface of the kidney proper is seen to consist of two distinct 

 parts; an outer or cortical portion, and an inner or medul- 

 lary. The medullary portion is less red and more glistening 

 to the eye, is finely striated in a radial direction, and does not 

 consist of one continuous mass but of a number of conical 

 portions, the pyramids of Malpighi, 2', each of which is 

 separated from its neighbors by an inward prolongation, *, of 

 the cortical substance: this, however, does not reach to the 

 inner end of the pyramid, which projects, as the papilla, into 

 a calyx of the ureter. At its outer end each pyramid sepa- 

 rates into smaller portions, the pyramids of Ferrein, 2", 

 separated by thin layers of cortex and gradually spreading 

 everywhere into the latter. The cortical substance is redder 

 and more granular looking and less shiny than the medullary, 

 and forms everywhere the outer layer of the organ next its 

 capsule, besides dipping in between the pyramids in the way 

 described. 



The renal artery divides in the hilus into branches (5) 

 which run into the kidney between the pyramids, giving off 

 a few twigs to the latter and ending finally in a much richer 

 vascular network in the cortex. The branches of the renal 

 vein have a similar course. 



The Minute Structure of the Kidney. The kidneys 

 are compound tubular glands, composed essentially of 

 branched microscopic urimferous tubules, lined by epithe- 

 lium. Each tubule commences at a small opening on a 

 papilla and from thence has a very complex course to its 

 other extremity: usually about twenty open, side by side, 

 on one papilla, where they have a diameter of about 0.125 

 mm. ( 5 Jo ich). Running from this place into the pyramid 





