SIXTEENTH LECTURE. 



THE KIDNEY, WITH THE URINARY PASSAGES. 



The structure of the mammalial kidney is extremely com- 

 plicated. This bean-shaped organ is covered by a not very 

 thick, but resistent, connective-tissue envelope. The blood- 

 vessels and lymphatics pass in and out at the hilus, and the 

 efferent canal, the ureter, also has its exit at this point. 



The kidney (Fig. 150), consists of two 

 different layers, a cortical, and a medul- 

 lary substance. The former (above, /), 

 appears to the naked eye dark and homo- 

 geneous ; the latter (a, b), paler, displays 

 a radiated fibrous arrangement. In most 

 mammals it projects in a single point into 

 the pelvis of the kidney (a). In man the 

 medullary substance is divided into a num- 

 ber of conical portions, with their bases 

 turned towards the cortex and their points 

 towards the hilus. 



These are the Malpighian or medullary 

 pyramids. The columnae Bertini are de- 

 pressions of the cortical substance between 

 the latter portions of these cones. 



The cortex and medulla are, further- 

 more, permeated by a connective-tissue 

 frame-work. 



The elements of the cortex, as well as 

 of the medulla, are long, glandular tubes, 

 the so-called uriniferous canals or Bellinian 

 tubes. 



In the medulla they divide frequently, 

 and run in a radial direction (b). They continue through the 



Fig. 150. — Diagram of 

 the mammalial kidney : 

 a, papilla; b, straight 

 uriniferous canals of the 

 medulla ; c, so-called 

 medullary rays of the 

 cortex ; d, outermost 

 cortical layer ; e, cortical 

 pyramids, with the arte- 

 ries connected with the 

 glomeruli ; f, border 

 layer. 



