STRUCTURE OF THE TUBULES. 



407 



The convoluted tubes {tuluU contorfi), which form the greater part of 

 the cortical substance, and, together ^vith vessels and connecting 

 Stroma, the whole of its outermost portion, vary m diameter, but corn- 

 Fig. 290. 



Fig 289 — Tr v^s^KR&l Sectio\ (I a Papilla or 



THE PiaS KlDNKY 400 DIAMFTERS (KoUlkei) 



a, a, collecting tubes with short columnai epithe- 

 lium , b, b, lu^er , t, c, smaller tubes of Henle , d, d, 

 blood-vessels. 





3. 



Yicf, 290. Tubes of Henle, prom the Pig's Kidney. 400 diameters (Kolliker). 



1, loop foi-med by the narrower variety of Henle's tube ; 2, passage of the broader 

 variety, a, into the narrower, h ; 3, loop formed by the broader variety of tube, with 

 granular epithelium. 



monly maintain the same average width as the smaller straight tubes, 

 namely -^Q^h of an inch. In the convoluted tubes the epithelium is 

 extremely granular, the nuclei are, in the fresh state, for the most part 

 obscured, and the epithelium in many cases almost fills the tubule, so 

 as to leave but a comparatively small lumen. In most animals it is 

 scarcely possible to make out the lines of junction between the 

 individual cells (fig. 288, h, from the dog), but in the human kidney the 

 latter are much more distinct (fig. 288, a, a'), being separated by clefts, 

 which extend almost to the basement membrane. 



