148 EXCRETION. 



Pyramidal Substance. Each papilla, as it projects into 

 the pelvis of the kidney, presents from two hundred to 

 five hundred little openings, from -g-J-g- to y^- of an inch in 

 diameter. 1 The tubes leading from the pelvis immediately 

 divide at very acute angles, generally dichotomatously, 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 nearly parallel with 

 each other. These are called the straight tubes of the kid- 

 ney, or the tubes of Bellini. They extend from the apices 

 of the pyramids to their bases, and pass then into the corti- 

 cal substance. The pyramids contain, in addition to the 

 straight tubes, a delicate fibrous matrix and numerous blood- 

 vessels; which latter, for the most part, pass beyond the 

 pyramids, to be finally distributed in the cortical substance. 

 Recent researches have shown that some of the convoluted 

 tubes dip down into the pyramids, returning to the cortical 

 substance in the form of loops. This arrangement will be 

 fully described in connection with the cortical portion. 



The tubes of the pyramidal substance are composed of a 

 strong, structureless basement-membrane, lined with granu- 

 lar, nucleated cells. According to the researches of Bow- 

 man, the tubes measure from -g-J-g- to -%fa of an inch in diame- 

 ter at the apices, and near the bases of the pyramids their 

 diameter is about -g-J-g- of an inch. 3 The membrane of the 

 tubes is dense and resisting, and portions of it with the epi- 

 thelial lining removed can generally be seen in microscopical 

 examinations, when the pyramidal substance has been sim- 

 ply lacerated with needles. This membrane is from 3ooo0 

 to 20000 of an inch in thickness. 8 



The cells lining the straight tubes exist in a single layer 



delphia, 1857, p. 789. This is the idea advanced in nearly all works on physi- 

 ology, when any opinion is expressed with regard to the relative activity of the 

 cortical and the pyramidal portions of the kidney. 



1 KOLLIKER, Manual of Human Microscopic Anatomy, London, 1860, p. 404. 



8 TODD AND BOWMAN, op. cit., p. 793. 



3 KOLLIKER, op. tit., p. 406. 



