ANATOMY OF THE KIDNEYS. 155 



after a long and tortuous ramification in the cortical sub- 

 stance, invariably become continuous, near the pyramids, 

 with tubes of much smaller diameter, which form loops, ex- 

 tending to a greater or less depth into the pyramids. The 

 loops formed by these canals (the narrow tubes of Henle) are 

 nearly parallel with the tubes of Bellini, and are much more 

 numerous near the bases of the pyramids than toward the 

 apices. 1 The diameter of these tubes is very variable, and 

 they present enlargements at irregular intervals in their 

 course. The narrow portions are about 2 ^ QO of an inch in 

 diameter, and the wide portions, about twice this size. Ac- 

 cording to Gross, this narrow portion is never absent, and is 

 lined by small, clear cells with very prominent nuclei. 8 The 

 wider portions are lined by larger granular cells. JSTear the 

 bases of the pyramids, the wide portion sometimes forms the 

 loop ; but near the apices, the loop is always narrow. The 

 difference in the size of the epithelium is such, that while 

 the diameter of the tube is variable, its calibre remains nearly 

 uniform. The membrane of these tubes is quite thick, 

 thicker, even, than the membrane of the tubes of Bellini. 



Intermediate Tubes. After the narrow tubes of Henle 

 have returned to the cortical substance, the^ communicate 

 with a system of flattened, ribbon-shaped canals, measuring 

 from 12 1 00 to 10 1 00 of an inch in diameter, with excessively 

 thin, fragile walls, lined by clear pavement-epithelium. 

 These tubes take an irregular and somewhat angular course 

 between the true convoluted tubes, and finally empty into 

 the branches of the straight tubes of Bellini, thus estab- 



tubes with the large convoluted tubes of the cortical substance and the tubes 

 of Bellini, as has been done by later investigators. An excellent review of the 

 views of Henle on this subject is given by Gross (loc. cit., p. 6, et seq.}. The 

 connection of these tubes with the ordinary convoluted tubes, and through them 

 with the Malpighian bodies, has been fully established by the very elaborate 

 researches of Schweigger-Seidel. (Die Nieren des Henschen, Halle, 1865, Taf. iv.) 



1 Most of the facts with regard to these looped canals we have recently 

 been enabled to verify in a very elegant section of the kidney of the human 

 subject, prepared by Dr. R. T. Edes, of Boston Highlands, Mass. 



8 GROSS, op. cit., p. 26. 



