PHYSIOLOGICAL ANATOMY OF THE KIDNEYS 



325 



ately divide at very acute angles, usually dichotomously, until a bundle 

 of tubes arises, as it were, from each opening. These bundles constitute 

 the pyramids of Ferrein. In their course the tubes are slightly wavy 

 and are nearly parallel with each other. These are called the straight 

 (collecting) tubes of the kidney, or the tubes of Bellini. They extend 

 from the apices of the pyramids to their bases and pass then into the 

 cortical substance. The pyramids contain,- in addition to the straight 

 tubes, a delicate fibrous matrix and bloodvessels, which latter usually 

 pass beyond the pyramids, to be finally distributed in the cortical sub- 

 stance. Small tubes, continuous with the convoluted tubes of the 

 cortical substance, dip down into the pyramids, returning to the cortical 

 substance in the form of loops. 

 The tubes of the pyramidal 

 substance are composed of a 

 strong structureless basement- 

 membrane lined with granular 

 nucleated cells. They measure 



3<h> to 2<W of an inch ( 8 5 to 

 127 /Lt) in diameter at the apices, 

 and near the bases of the pyra- 

 mids their diameter is about g-J-g- 

 of an inch (42 JJL). 



The cells lining the straight 

 tubes exist in a single layer ap- 

 plied to the basement-membrane. 

 They are thick and irregularly 



polygonal in shape, with abim- Fi S-73- Collecting tubes of the kidney, x 130, hema- 



toxylin and eosin (Author's collection). 



dant albuminous granules. They 



present one, and occasionally, though rarely, two granular nuclei, with 

 one or two nucleoli. They readily undergo alteration and are seen in 

 their normal condition only in a perfectly fresh healthy kidney. Their 

 diameter is about y^Vo f an mcn ( I 7 /*) The cau bre of the tubes is 

 reduced by the thickness of their lining epithelium to -9^ or ^^ of an 

 inch (28 or 30 /it). 



Cortical Substance. In the cortical portion of the kidney are found 

 tubes, differing somewhat from the tubes of the pyramidal portion in 

 their size and in the character of their epithelial lining, and presenting 

 a marked difference in their direction. These tubes are rather larger 

 than the tubes of the pyramidal substance, and are convoluted, inter- 

 lacing with each other in every direction. Scattered pretty uniformly 

 throughout this portion of the kidney, are rounded or ovoid bodies, 

 about four times the diameter of the convoluted tubes, known as the 



