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MANUAL OF HISTOLOGY. 



cal and medullary substances ; they are of different diameters 

 and pursue either a straight or tortuous course. Some have a 

 basement membrane (membrana or tunica propria), on which 

 the epithelium rests ; others appear to have none. The tu- 

 bules are clothed with epithelium of different varieties. Speci- 

 mens' should be made from a kidney that has lain for twenty- 

 four hours in a 5 per cent, solution of chromic acid. A small 



FIG. 91. Schematic representation of the kidney : A, medulla ; B, boundary layer ; C, cortical por- 

 tion ; a, renal artery ; b, renal vein ; c, artery penetrating cortex ; D, capsule enclosing glomerulus ; E, 

 capillaries ; F, convoluted tubules of first order ; G, looped tubule, descending branch ; H, looped tubule, 

 ascending branch ; I, convoluted tubule of second order ; J, collecting tubule ; K, vasa recta. 



piece of the gland is to be placed on a slide, and a drop of glycer- 

 ine added ; the tubules may be isolated by teasing with needles. 

 In Fig. 91 there is a schematic representation of the vascular 

 distribution and course of the tubules in one of the pyramids. 

 Each tubule takes its origin in an expansion that surrounds 

 the glomerulus, and is called Bowman ' s or Mullens capsule. 1 



1 Miiller, in 1830, described the capsules, but regarded them as vesicles which had 

 no connection whateyer with the uriniferous tubules. Bowman, in Philosoph. Trans; 

 act., 1843. 



