CH. XXXVIII.] THE KIDNEY TUBULES 567 



In the pyramids the tubes are straight uniting to form larger 

 tubes as they descend through these from the cortical portion;, 

 while in the latter region they are convoluted. But in the boundary 

 zone between cortex and medulla, small collections of straight tubes 

 called medullary rays project into the cortical region. 



Each begins in the cortex as a dilatation, called the Capsule of 

 Bowman ; this encloses a tuft or glomerulus of capillaries, called a 

 Malpighian corpuscle. The tubule leaves the capsule by a neck, and 





FIG. 372. Malpighian corpuscle, injected through the renal artery with coloured gelatin ; a, glomerular 

 vessels ; b, c, capsule of Bowman ; (/, afferent vessel of glomerulus ; e, efferent vessels ; 

 /, epithelium of tubes. (Cadiat.) 



then becomes convoluted (first convoluted tubule), but soon after 

 becomes nearly straight or slightly spiral (spiral tubule) ; then rapidly 

 narrowing, it passes down into the medulla as the descending tubule of 

 Henle ; this turns round, forming a loop (loop of Henle), and passes 

 up to the cortex again as the ascending tubule of Henle. It then 

 becomes larger and irregularly zigzag (zigzag tubule) and again con- 

 voluted (second convoluted tubule). Eventually it narrows into a 

 junctional tubule, which joins a straight or collecting tubule. This 

 passes straight through the medulla, where it joins with others to 

 form one of the ducts of Bellini that open at the apex of the pyramid. 

 These parts are all shown in fig. 371. 



In the capsule, the epithelium is flattened and reflected over the 

 glomerulus, 



